Syllacon NOTES PHYSICS OUTLINE SINGAPORE-CAMBRIDGE GCE O-LEVEL SYLLABUS 5059

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1 Syllacon NOTES SINGAPORE-CAMBRIDGE GCE O-LEVEL PHYSICS OUTLINE SYLLABUS 5059 UPDATED 20 JAN 2014

2 Overview Themes Chapters Count I. Measurement 1 1 II. Newtonian Mechanics III. Thermal Physics IV. Waves V. Electricity & Magnetism Physical Quantities, Units and Measurement Kinematics Dynamics Mass, Weight and Density Turning Effect of Forces Pressure Energy, Work and Power Kinetic Model of Matter Transfer of Thermal Energy Temperature Thermal Properties of Matter General Wave Properties Light Electromagnetic Spectrum Sound Static Electricity Current of Electricity D.C. Circuits Practical Electricity Magnetism Electromagnetism Electromagnetic Induction Note to student: Spot an error? Think that you can improve the outline? Download the.docx format of this document from the website and edit the outline yourself! Alternatively, you may wish to the site owner at lim.ting.jie.2012@vjc.sg with the subject title: Outline Feedback: O Level Physics Outline 2 Consylladated by Lim Ting Jie

3 Contents 1. Physical Quantities, Units and Measurement (a) show understanding that all physical quantities consist of a numerical magnitude and a unit12 (b) recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol) (c) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G) (d) show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth (e) state what is meant by scalar and vector quantities and give common examples of each (f) add two vectors to determine a resultant by a graphical method (g) describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary (h) describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments Kinematics (a) state what is meant by speed and velocity (b) calculate average speed using distance travelled / time taken (c) state what is meant by uniform acceleration and calculate the value of an acceleration using change in velocity / time taken (d) interpret given examples of non-uniform acceleration (e) plot and interpret a displacement-time graph and a velocity-time graph (f) deduce from the shape of a displacement-time graph when a body is: (i) at rest (ii) moving with uniform velocity (iii) moving with non-uniform velocity (g) deduce from the shape of a velocity-time graph when a body is: (i) at rest (ii) moving with uniform velocity (iii) moving with uniform acceleration (iv) moving with non-uniform acceleration (h) calculate the area under a velocity-time graph to determine the displacement travelled for motion with uniform velocity or uniform acceleration (i) state that the acceleration of free fall for a body near to the Earth is constant and is approximately 10 m/s (j) describe the motion of bodies with constant weight falling with or without air resistance, including reference to terminal velocity Dynamics (a) apply Newton's Laws to: (i) describe the effect of balanced and unbalanced forces on a body (ii) describe the ways in which a force may change the motion of a body (iii) identify actionreaction pairs acting on two interacting bodies (stating of Newton's Laws is not required) (b) identify forces acting on an object and draw free body diagram(s) representing the forces acting on the object (for cases involving forces acting in at most 2 dimensions) Consylladated by Lim Ting Jie

4 (c) solve problems for a static point mass under the action of 3 forces for 2-dimensional cases (a graphical method would suffice) (d) recall and apply the relationship resultant force = mass acceleration to new situations or to solve related problems (e) explain the effects of friction on the motion of a body Mass, Weight and Density (a) state that mass is a measure of the amount of substance in a body (b) state that mass of a body resists a change in the state of rest or motion of the body (inertia) (c) state that a gravitational field is a region in which a mass experiences a force due to gravitational attraction (d) define gravitational field strength, g, as gravitational force per unit mass (e) recall and apply the relationship weight = mass gravitational field strength to new situations or to solve related problems (f) distinguish between mass and weight (g) recall and apply the relationship density = mass / volume to new situations or to solve related problems Turning Effect of Forces (a) describe the moment of a force in terms of its turning effect and relate this to everyday examples (b) recall and apply the relationship moment of a force (or torque) = force perpendicular distance from the pivot to new situations or to solve related problems (c) state the principle of moments for a body in equilibrium (d) apply the principle of moments to new situations or to solve related problems (e) show understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity (f) describe qualitatively the effect of the position of the centre of gravity on the stability of objects Pressure (a) define the term pressure in terms of force and area (b) recall and apply the relationship pressure = force / area to new situations or to solve related problems (c) describe and explain the transmission of pressure in hydraulic systems with particular reference to the hydraulic press (d) recall and apply the relationship pressure due to a liquid column = height of column density of the liquid gravitational field strength to new situations or to solve related problems (e) describe how the height of a liquid column may be used to measure the atmospheric pressure (f) describe the use of a manometer in the measurement of pressure difference Energy, Work and Power (a) show understanding that kinetic energy, potential energy (chemical, gravitational, elastic), light energy, thermal energy, electrical energy and nuclear energy are examples of different forms of energy (b) state the principle of the conservation of energy and apply the principle to new situations or to solve related problems Consylladated by Lim Ting Jie

5 (c) calculate the efficiency of an energy conversion using the formula efficiency = energy converted to useful output / total energy input (d) state that kinetic energy E k = ½ mv 2 and gravitational potential energy E p = mgh (for potential energy changes near the Earth s surface) (e) apply the relationships for kinetic energy and potential energy to new situations or to solve related problems (f) recall and apply the relationship work done = force distance moved in the direction of the force to new situations or to solve related problems (g) recall and apply the relationship power = work done / time taken to new situations or to solve related problems Kinetic Model of Matter (a) compare the properties of solids, liquids and gases (b) describe qualitatively the molecular structure of solids, liquids and gases, relating their properties to the forces and distances between molecules and to the motion of the molecules. 32 (c) infer from Brownian motion experiment the evidence for the movement of molecules (d) describe the relationship between the motion of molecules and temperature (e) explain the pressure of a gas in terms of the motion of its molecules (f) recall and explain the following relationships using the kinetic model (stating of the corresponding gas laws is not required): (i) a change in pressure of a fixed mass of gas at constant volume is caused by a change in temperature of the gas (ii) a change in volume occupied by a fixed mass of gas at constant pressure is caused by a change in temperature of the gas (iii) a change in pressure of a fixed mass of gas at constant temperature is caused by a change in volume of the gas (g) use the relationships in (f) in related situations and to solve problems (a qualitative treatment would suffice) Transfer of Thermal Energy (a) show understanding that thermal energy is transferred from a region of higher temperature to a region of lower temperature (b) describe, in molecular terms, how energy transfer occurs in solids (c) describe, in terms of density changes, convection in fluids (d) explain that energy transfer of a body by radiation does not require a material medium and the rate of energy transfer is affected by: (i) colour and texture of the surface (ii) surface temperature (iii) surface area (e) apply the concept of thermal energy transfer to everyday applications Temperature (a) explain how a physical property which varies with temperature, such as volume of liquid column, resistance of metal wire and electromotive force (e.m.f.) produced by junctions formed with wires of two different metals, may be used to define temperature scales (b) describe the process of calibration of a liquid-in-glass thermometer, including the need for fixed points such as the ice point and steam point Thermal Properties of Matter (a) describe a rise in temperature of a body in terms of an increase in its internal energy (random thermal energy) Consylladated by Lim Ting Jie

6 (b) define the terms heat capacity and specific heat capacity (c) recall and apply the relationship thermal energy = mass specific heat capacity change in temperature to new situations or to solve related problems (d) describe melting/solidification and boiling/condensation as processes of energy transfer without a change in temperature (e) explain the difference between boiling and evaporation (f) define the terms latent heat and specific latent heat (g) recall and apply the relationship thermal energy = mass specific latent heat to new situations or to solve related problems (h) explain latent heat in terms of molecular behaviour (i) sketch and interpret a cooling curve General Wave Properties (a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs and by waves in a ripple tank (b) show understanding that waves transfer energy without transferring matter (c) define speed, frequency, wavelength, period and amplitude (d) state what is meant by the term wavefront (e) recall and apply the relationship velocity = frequency wavelength to new situations or to solve related problems (f) compare transverse and longitudinal waves and give suitable examples of each Light (a) recall and use the terms for reflection, including normal, angle of incidence and angle of reflection (b) state that, for reflection, the angle of incidence is equal to the angle of reflection and use this principle in constructions, measurements and calculations (c) recall and use the terms for refraction, including normal, angle of incidence and angle of refraction (d) recall and apply the relationship sin i / sin r = constant to new situations or to solve related problems (e) define refractive index of a medium in terms of the ratio of speed of light in vacuum and in the medium (f) explain the terms critical angle and total internal reflection (g) identify the main ideas in total internal reflection and apply them to the use of optical fibres in telecommunication and state the advantages of their use (h) describe the action of a thin lens (both converging and diverging) on a beam of light (i) define the term focal length for a converging lens (j) draw ray diagrams to illustrate the formation of real and virtual images of an object by a thin converging lens Electromagnetic Spectrum (a) state that all electromagnetic waves are transverse waves that travel with the same speed in vacuum and state the magnitude of this speed Consylladated by Lim Ting Jie

7 (b) describe the main components of the electromagnetic spectrum (c) state examples of the use of the following components: (i) radiowaves (e.g. radio and television communication) (ii) microwaves (e.g. microwave oven and satellite television) (iii) infra-red (e.g. infra-red remote controllers and intruder alarms) (iv) light (e.g. optical fibres for medical uses and telecommunications) (v) ultra-violet (e.g. sunbeds and sterilisation) (vi) X-rays (e.g. radiological and engineering applications) (vii) gamma rays (e.g. medical treatment) (d) describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and damage to living cells and tissue Sound (a) describe the production of sound by vibrating sources (b) describe the longitudinal nature of sound waves in terms of the processes of compression and rarefaction (c) explain that a medium is required in order to transmit sound waves and the speed of sound differs in air, liquids and solids (d) describe a direct method for the determination of the speed of sound in air and make the necessary calculation (e) relate loudness of a sound wave to its amplitude and pitch to its frequency (f) describe how the reflection of sound may produce an echo, and how this may be used for measuring distances (g) define ultrasound and describe one use of ultrasound, e.g. quality control and pre-natal scanning Static Electricity (a) state that there are positive and negative charges and that charge is measured in coulombs (b) state that unlike charges attract and like charges repel (c) describe an electric field as a region in which an electric charge experiences a force (d) draw the electric field of an isolated point charge and recall that the direction of the field lines gives the direction of the force acting on a positive test charge (e) draw the electric field pattern between two isolated point charges (f) show understanding that electrostatic charging by rubbing involves a transfer of electrons (g) describe experiments to show electrostatic charging by induction (h) describe examples where electrostatic charging may be a potential hazard (i) describe the use of electrostatic charging in a photocopier, and apply the use of electrostatic charging to new situations Current of Electricity (a) state that current is a rate of flow of charge and that it is measured in amperes (b) distinguish between conventional current and electron flow (c) recall and apply the relationship charge = current time to new situations or to solve related problems (d) define electromotive force (e.m.f.) as the work done by a source in driving unit charge around a complete circuit (e) calculate the total e.m.f. where several sources are arranged in series Consylladated by Lim Ting Jie

8 (f) state that the e.m.f. of a source and the potential difference (p.d.) across a circuit component is measured in volts (g) define the p.d. across a component in a circuit as the work done to drive unit charge through the component (h) state the definition that resistance = p.d. / current (i) apply the relationship R = V/I to new situations or to solve related problems (j) describe an experiment to determine the resistance of a metallic conductor using a voltmeter and an ammeter, and make the necessary calculations (k) recall and apply the formulae for the effective resistance of a number of resistors in series and in parallel to new situations or to solve related problems (l) recall and apply the relationship of the proportionality between resistance and the length and cross-sectional area of a wire to new situations or to solve related problems (m) state Ohm s Law (n) describe the effect of temperature increase on the resistance of a metallic conductor (o) sketch and interpret the I/V characteristic graphs for a metallic conductor at constant temperature, for a filament lamp and for a semiconductor diode D.C. Circuits (a) draw circuit diagrams with power sources (cell, battery, d.c. supply or a.c. supply), switches, lamps, resistors (fixed and variable), variable potential divider (potentiometer), fuses, ammeters and voltmeters, bells, light-dependent resistors, thermistors and light-emitting diodes (b) state that the current at every point in a series circuit is the same and apply the principle to new situations or to solve related problems (c) state that the sum of the potential differences in a series circuit is equal to the potential difference across the whole circuit and apply the principle to new situations or to solve related problems (d) state that the current from the source is the sum of the currents in the separate branches of a parallel circuit and apply the principle to new situations or to solve related problems (e) state that the potential difference across the separate branches of a parallel circuit is the same and apply the principle to new situations or to solve related problems (f) recall and apply the relevant relationships, including R = V/I and those for current, potential differences and resistors in series and in parallel circuits, in calculations involving a whole circuit (g) describe the action of a variable potential divider (potentiometer) (h) describe the action of thermistors and light-dependent resistors and explain their use as input transducers in potential dividers (i) solve simple circuit problems involving thermistors and lightdependent resistors Practical Electricity (a) describe the use of the heating effect of electricity in appliances such as electric kettles, ovens and heaters (b) recall and apply the relationships P = VI and E = VIt to new situations or to solve related problems (c) calculate the cost of using electrical appliances where the energy unit is the kw h (d) compare the use of non-renewable and renewable energy sources such as fossil fuels, nuclear energy, solar energy, wind energy and hydroelectric generation to generate electricity in terms of energy conversion efficiency, cost per kw h produced and environmental impact Consylladated by Lim Ting Jie

9 (e) state the hazards of using electricity in the following situations: (i) damaged insulation (ii) overheating of cables (iii) damp conditions (f) explain the use of fuses and circuit breakers in electrical circuits and of fuse ratings (g) explain the need for earthing metal cases and for double insulation (h) state the meaning of the terms live, neutral and earth (i) describe the wiring in a mains plug (j) explain why switches, fuses, and circuit breakers are wired into the live conductor Magnetism (a) state the properties of magnets (b) describe induced magnetism (c) describe electrical methods of magnetisation and demagnetisation (d) draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets (e) describe the plotting of magnetic field lines with a compass (f) distinguish between the properties and uses of temporary magnets (e.g. iron) and permanent magnets (e.g. steel) Electromagnetism (a) draw the pattern of the magnetic field due to currents in straight wires and in solenoids and state the effect on the magnetic field of changing the magnitude and/or direction of the current 71 (b) describe the application of the magnetic effect of a current in a circuit breaker (c) describe experiments to show the force on a current-carrying conductor, and on a beam of charged particles, in a magnetic field, including the effect of reversing (i) the current (ii) the direction of the field (d) deduce the relative directions of force, field and current when any two of these quantities are at right angles to each other using Fleming s left-hand rule (e) describe the field patterns between currents in parallel conductors and relate these to the forces which exist between the conductors (excluding the Earth s field) (f) explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing (i) the number of turns on the coil (ii) the current (g) discuss how this turning effect is used in the action of an electric motor (h) describe the action of a split-ring commutator in a two-pole, single-coil motor and the effect of winding the coil on to a soft-iron cylinder Electromagnetic Induction (a) deduce from Faraday s experiments on electromagnetic induction or other appropriate experiments: (i) that a changing magnetic field can induce an e.m.f. in a circuit (ii) that the direction of the induced e.m.f. opposes the change producing it (iii) the factors affecting the magnitude of the induced e.m.f (b) describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings (where needed) (c) sketch a graph of voltage output against time for a simple a.c. generator Consylladated by Lim Ting Jie

10 (d) describe the use of a cathode-ray oscilloscope (c.r.o.) to display waveforms and to measure potential differences and short intervals of time (detailed circuits, structure and operation of the c.r.o. are not required) (e) interpret c.r.o. displays of waveforms, potential differences and time intervals to solve related problems (f) describe the structure and principle of operation of a simple iron-cored transformer as used for voltage transformations (g) recall and apply the equations V P / V S = N P / N S and V P I P = V S I S to new situations or to solve related problems (for an ideal transformer) (h) describe the energy loss in cables and deduce the advantages of high voltage transmission Consylladated by Lim Ting Jie

11 SECTION I: MEASUREMENT Overview In order to gain a better understanding of the physical world, scientists use a process of investigation that follows a general cycle of observation, hypothesis, deduction, test and revision, sometimes referred to as the scientific method. Galileo Galilei, one of the earliest architects of this method, believed that the study of science had a strong logical basis that involved precise definitions of terms and physical quantities, and a mathematical structure to express relationships between these physical quantities. In this section, we study a set of base physical quantities and units that can be used to derive all other physical quantities. These precisely defined quantities and units, with accompanying orderof-ten prefixes (e.g. milli, centi and kilo) can then be used to describe the interactions between objects in systems that range from celestial objects in space to sub-atomic particles. Extracted from PHYSICS GCE ORDINARY LEVEL (2014) Syllabus Document 11 Consylladated by Lim Ting Jie

12 1. Physical Quantities, Units and Measurement syllacon.weebly.com Content Physical quantities SI units Prefixes Scalars and vectors Measurement of length and time Learning Outcomes Candidates should be able to: (a) show understanding that all physical quantities consist of a numerical magnitude and a unit Term Definition Constituents Physical quantity Quantity that can be measured [no need to remember this definition] A numerical magnitude A unit (b) recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K), amount of substance (mol) Term Base quantity (Derived quantities, e.g. area, are derived from base quantities, e.g. length) Type Mass Length Time Current Temperature Amount of substance SI unit kilograms metres seconds amperes Kelvin mole Unit symbol kg m s A K mol (c) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M), giga (G) Magnitude +ve sign prefix (symbol) ve sign prefix (symbol) Examples (where 1 y < 10) 10 ±1 deca- (da) deci- (d) y kg = y 10 3 g 10 ±2 hexa- (h) centi- (c) y cm = y 10 2 m y cm 2 = y 10 4 m 2 10 ±3 kilo- (k) milli- (m) y cm 3 = y 10 6 m 3 y m = y 10 2 cm 10 ±6 mega- (M) micro- (µ) y m 2 = y 10 4 cm 2 10 ±9 giga- (G) nano- (n) y m 3 = y 10 6 cm 3 (d) show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth Object H atom Chopsticks length Football field length Mount Everest s height Earth s radius Magnitude m m m m m Note: There is no need to remember these magnitudes, an appreciation will do 12 Consylladated by Lim Ting Jie

13 (e) state what is meant by scalar and vector quantities and give common examples of each Term Scalar quantity Vector quantity Definition Physical quantities that have magnitude only Physical quantities that possess both magnitude and direction Examples Scalar Distance Speed Energy Mass Vector Displacement Velocity Force Weight (f) add two vectors to determine a resultant by a graphical method Determination of resultant force Case Case 1: Parallel vectors Case 2a: Same origin Case 2: Non-parallel vectors Case 2b: Tip-to-tail Steps Step 1: Calculate resultant force Step 1: Write down the scale using 1 cm :? N (scale must allow diagram drawn to be more than half of the space given in question) Step 2: Draw the 2 forces with single arrows according to the scale Step 3: Finish the parallelogram with dotted lines using set square Step 4: Draw resultant force from the origin with a double arrow Step 5: Measure length of resultant force Step 6: Calculate resultant force Step 1: Write down the scale using 1 cm :? N (scale must allow diagram drawn to be more than half of the space given in question) Step 2: Draw the 2 forces with single arrows according to the scale Step 3: Draw resultant force from the start to end of the 2 forces with a double arrow Step 4: Measure length of resultant force Step 5: Calculate resultant force 3N 5N Scale: 1 cm : 0.5 N Scale: 1 cm : 0.5 N Example Resultant force = 5N 3N = 2N in the forward direction 3 N 5 N 40 o 18 o 20 o 7 N 3 N 5 N 40 o 20 o 76 o 4.4 N Resultant force = = 7 N, acting 18 o to the horizontal Resultant force = = 7 N, acting o to the horizontal 13 Consylladated by Lim Ting Jie

14 (g) describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary # Instrument Precision Purpose Method of measurement Possible error 1 Tape 10 1 cm To measure widths (e.g. long distances) 2 Metre rule 10 1 cm To measure depths (e.g. of ponds) 3 Caliper 10 1 cm To measure circular objects To measure cylinders Position eye directly above the markings on the tape when making measurement to avoid parallax error Measure from a randomly chosen point instead of the ends to avoid zero error (from wear and tear) Substract the reading at the start of the object from the reading at the end of the object Circular objects Use jaws of the external calipers to grip the widest part of the circular object Distance between jaws is measured with a metre rule Cylinders Invert the jaws to use the internal calipers Use jaws of the internal calipers to measure the inner diameter of the cylinder Distance between jaws is measured with a metre rule Parallax error Parallax error Parallax error 4 Vernier caliper 10 2 cm To measure the internal and external diameters of an object Consists of a main scale and a sliding vernier scale Grip the object using the correct pair of jaws Read the main scale directly opposite the zero mark on the vernier scale (e.g. 2.4 cm) Read the vernier mark that coincides with a marking on the main scale (e.g cm) Close the vernier caliper to check for zero error to be corrected (e.g cm) Calculate the final reading by adding the vernier reading and substracting the zero error [e.g (+0.03) (+0.02) = 2.41 cm] Zero error 5 Micrometer screw gauge 10 3 cm To measure the external diameter of small precision (e.g. wires, ball bearings) Turn the thimble such that the object is gripped gently Turn the ratchet until it starts to click Read the main scale reading at the edge of the thimble (e.g. 6.5 mm) Read the thimble scale reading (reading 35 indicates 0.35 mm) Close the micrometer screw guage to check for zero error to be corrected (e.g mm) Calculate the final reading by adding the vernier reading and substracting the zero error [e.g (+0.35) (+0.02) = 6.65 cm] Zero error Note: This is mainly important for practical sessions 14 Consylladated by Lim Ting Jie

15 (h) describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments Term Oscillation Period Meaning as for a pendulum Each complete to-and-fro motion of the pendulum bob Time taken for one complete oscillation Instrument Precision Method of measurement of pendulum period Factors affecting period of the pendulum Possible error Stopwatch 10 2 s Measure the time taken for the pendulum to make 20 oscillations Find the period accurately by dividing the total time by 20 Note: This is mainly important for practical sessions Length of string affects the period Mass of bob does not affect the period Human reaction time (about 0.3 to 0.5 s) 15 Consylladated by Lim Ting Jie

16 Overview SECTION II: NEWTONIAN MECHANICS Mechanics is the branch of physics that deals with the study of motion and its causes. Through a careful process of observation and experimentation, Galileo Galilei used experiments to overturn Aristotle s ideas of the motion of objects, for example the flawed idea that heavy objects fall faster than lighter ones, which dominated physics for about 2,000 years. The greatest contribution to the development of mechanics is by one of the greatest physicists of all time, Isaac Newton. By extending Galileo s methods and understanding of motion and gravitation, Newton developed the three laws of motion and his law of universal gravitation, and successfully applied them to both terrestrial and celestial systems to predict and explain phenomena. He showed that nature is governed by a few special rules or laws that can be expressed in mathematical formulae. Newton s combination of logical experimentation and mathematical analysis shaped the way science has been done ever since. In this section, we begin by examining kinematics, which is a study of motion without regard for the cause. After which, we study the conditions required for an object to be accelerated and introduce the concept of forces through Newton s Laws. Subsequently, concepts of moments and pressure are introduced as consequences of a force. Finally, this section rounds up by leading the discussion from force to work and energy, and the use of the principle of conservation of energy to explain interactions between bodies. Extracted from PHYSICS GCE ORDINARY LEVEL (2014) Syllabus Document 16 Consylladated by Lim Ting Jie

17 2. Kinematics syllacon.weebly.com Content Speed, velocity and acceleration Graphical analysis of motion Free-fall Effect of air resistance Learning Outcomes Candidates should be able to: (a) state what is meant by speed and velocity Term Average speed Velocity Definition Total distance travelled per unit time Change in displacement per unit time (b) calculate average speed using distance travelled / time taken Term Average speed Formula Distance Average speed Time taken (c) state what is meant by uniform acceleration and calculate the value of an acceleration using change in velocity / time taken Common legend Key t a u v s Term Time taken Acceleration Initial velocity Final velocity Displacement Term Definition Formulae Acceleration Change in velocity per unit time Change in velocity Acceleration Time taken v u a t Uniform acceleration Constant change in velocity per unit time N.A. Related formulae to find acceleration Given Formula to use Time taken & Final velocity v u at Time taken & Displacement 1 2 s ut at Final velocity & Displacement 2 2 v u 2as 2 17 Consylladated by Lim Ting Jie

18 (d) interpret given examples of non-uniform acceleration Increasing acceleration Non-uniform acceleration Decreasing acceleration Uniform acceleration Pushing on the pedal Releasing force on the pedal No change in force exerted on the pedal (e.g. pushing the pedal all the way) (e) plot and interpret a displacement-time graph and a velocity-time graph Differences Displacement-time graph Velocity-time graph Label of y-axis Displacement / m Velocity / m s -1 Label of x-axis Time / s Time / s Area below graph N.A. Total displacement / m Gradient of graph Velocity / m s -1 Acceleration / m s -2 (f) deduce from the shape of a displacement-time graph when a body is: (i) at rest (ii) moving with uniform velocity (iii) moving with non-uniform velocity Displacement-time graph Scenarios Displacement Gradient At rest Zero displacement N.A. Moving with uniform velocity Increasing displacement Constant gradient Moving with non-uniform velocity Varying displacement Varying gradient (g) deduce from the shape of a velocity-time graph when a body is: (i) at rest (ii) moving with uniform velocity (iii) moving with uniform acceleration (iv) moving with non-uniform acceleration Velocity-time graph Scenarios Velocity Gradient At rest Zero velocity N.A. Moving with uniform velocity Constant velocity Zero gradient Moving with uniform acceleration Increasing velocity Constant gradient Moving with non-uniform acceleration Varying velocity Varying gradient 18 Consylladated by Lim Ting Jie

19 (h) calculate the area under a velocity-time graph to determine the displacement travelled for motion with uniform velocity or uniform acceleration Term Formulae Displacement Displacement Area under velocity-time graph Area of square Velocity Time taken 1 2 Area of triangle Velocity Time taken Term Formulae in symbols Displacement s 1 v ut 2 Average velocity Average velocity 1 v u 2 (i) state that the acceleration of free fall for a body near to the Earth is constant and is approximately 10 m/s 2 Relationship between force and acceleration When a force is exerted on an object, the object will experience constant acceleration in the direction of the force if there is no other force acting against it (i.e. constant resultant force) Any free falling object near to the Earth will experience constant acceleration of approximately 10 m/s 2 due to gravity as there is no air resistance acting against it Acceleration will only decrease when the object enters Earth as it will then experience air resistance (j) describe the motion of bodies with constant weight falling with or without air resistance, including reference to terminal velocity Differences With air resistance Without air resistance Description of motion of bodies with constant weight Graph of velocity against time As an object falls in air, it increases its speed with an initial acceleration of 10ms -2 Air resistance opposing weight increases as speed increases, causing resultant force and hence acceleration to decrease When air resistance is equal to the weight of the body, the forces balance out to zero resultant force causing zero acceleration and the object travels at constant terminal velocity As an object falls in a vacuum, it increases its speed with an uniform acceleration of 10ms -2 This is because there is no air resistance present, thus resultant force is constant 19 Consylladated by Lim Ting Jie

20 3. Dynamics syllacon.weebly.com Content Balanced and unbalanced forces Free-body diagram Friction Learning Outcomes Candidates should be able to: (a) apply Newton's Laws to: (i) describe the effect of balanced and unbalanced forces on a body (ii) describe the ways in which a force may change the motion of a body (iii) identify action-reaction pairs acting on two interacting bodies (stating of Newton's Laws is not required) Scenarios Description Possible effects Condition Balanced forces on a body Resultant force is equal to 0 N Object at rest Object travels at constant speed in a straight line Object initially at rest Object initally in motion Unbalanced forces on a body Resultant force is more than 0 N Object accelerates Object decelerates Object is initially at rest or Force in same direction as object s motion Force in opposite direction to object s motion Object changes direction Force acts at an angle to object s motion Illustrations of unbalanced forces Object accelerates Object decelerates Object changes direction Term Meaning Example Relationship Action force Reaction force The force a body (body 1) exerts on another body (body 2) The subsequent force body 2 exerts on body 1 in reaction to the action force Feet of a swimmer pushing against the swimming pool wall Force that propels in swimmer forward in reaction Forces always occur in pairs, each made up of a action force and a reaction force Action and reaction forces are equal in magnitude, act in opposite directions and on 2 different bodies 20 Consylladated by Lim Ting Jie

21 (b) identify forces acting on an object and draw free body diagram(s) representing the forces acting on the object (for cases involving forces acting in at most 2 dimensions) Legend Key Term Explanation T Thrust N.A. W Weight of object Due to gravity F Force N.A. + F Contact force Reaction force due to weight of object * f Friction Between object and ground R Air resistance Friction between object and air molecules Air resistance applicable Object thrust upwards Object released high up Without air resistance With air resistance Air resistance not applicable Object on the ground Object pushed on the ground (c) solve problems for a static point mass under the action of 3 forces for 2-dimensional cases (a graphical method would suffice) References Refer to Learning Outcome 1(f) on Page Consylladated by Lim Ting Jie

22 (d) recall and apply the relationship resultant force = mass acceleration to new situations or to solve related problems Term Formula SI units Interpretation Resultant force Resultant force Mass Acceleration F ma F m a A resultant force of 2 N exerted on a body of mass 0.5 kg causes the N kg m s -2 body to accelerate at 4 m s -2 (e) explain the effects of friction on the motion of a body Scenario Possible motions Explanation Box rests on a flat horizontal floor Box slides along a rough table Box remains at rest Decelerates and eventually stops There is no frictional force acting on the box Contact force of the ground is equal to the weight of the box due to gravity Frictional force opposes the force of the motion Kinetic energy is converted to heat energy Box rests on a slope Box remains at rest Downward force of attraction acting on the box due to gravity is equal to the upward frictional force Resultant force is zero Box accelerates down the slope Downward force of attraction acting on the box due to gravity is more than the upward frictional force Resultant force is more than zero 22 Consylladated by Lim Ting Jie

23 4. Mass, Weight and Density syllacon.weebly.com Content Mass and weight Gravitational field and field strength Density Learning Outcomes Candidates should be able to: (a) state that mass is a measure of the amount of substance in a body (b) state that mass of a body resists a change in the state of rest or motion of the body (inertia) Term Mass Inertia Definition Measure of the amount of substance in a body which resists a change in the state of rest or motion of the body The resistance of a body with mass to start moving if it is stationary or stop moving if it is in motion in its first instance (c) state that a gravitational field is a region in which a mass experiences a force due to gravitational attraction Term Gravitational field Definition A region in which a mass experiences a force due to gravitational attraction (d) define gravitational field strength, g, as gravitational force per unit mass Term Gravitational field strength Definition Gravitational force acting per unit mass on an object The gravitational field strength on Earth is about 10 N kg -1 (e) recall and apply the relationship weight = mass gravitational field strength to new situations or to solve related problems Term Definition Formula SI units Interpretation Weight The force of attraction on an object due to gravity Weight Mass Gravitational field strength W mg g on Earth is about 10 N kg -1 W kg m N g N kg -1 A 2 kg mass has a weight of 20 N due to Earth s gravitational pull of 10 N kg Consylladated by Lim Ting Jie

24 (f) distinguish between mass and weight Differences Mass Weight Meaning Amount of matter in a body Due to pull of gravity on a body Scalar or vector Scalar; has only magnitude Vector; has both magnitude and direction Unit Measured in kg (kilograms) Measures in N (newtons) Variations Constant regardless of gravitational field strength Varies according to gravitational field strength (g) recall and apply the relationship density = mass / volume to new situations or to solve related problems Term Definition Formula SI units Interpretation Density Mass per unit volume Mass Density Volume m V m V An object with mass of 4 kg and volume of 2 m 3 has a density of 2 kg m -3 kg m -3 kg m 3 24 Consylladated by Lim Ting Jie

25 5. Turning Effect of Forces syllacon.weebly.com Content Moments Centre of gravity Stability Learning Outcomes Candidates should be able to: (a) describe the moment of a force in terms of its turning effect and relate this to everyday examples (b) recall and apply the relationship moment of a force (or torque) = force perpendicular distance from the pivot to new situations or to solve related problems Term Turning effect Definition The turning of an object about a pivot The greater the moment, the greater the object turns about the pivot Term Definition Formula SI units Interpretation Moment of a force The product of the force and the perpendicular distance between the line of action of the force and a pivot, and resulting in a turning effect Moment Force Perpendicular distance Moment F pd Moment F pd A force of 2 N acting with a perpendicular distance of Nm N m 2 m produces a moment of 4 Nm (c) state the principle of moments for a body in equilibrium (d) apply the principle of moments to new situations or to solve related problems Term Definition Formula Principle of moments When an object is in equilibrium, the sum of clockwise moments about a pivot is equal to sum of anticlockwise moments about the same pivot Sum of clockwise moments Sum of anti-clockwise moments (e) show understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity Term Definition Alternative definition Centre of gravity of an object Point of application of the resultant force on an object exerted by gravity for any orientation of the object Point through which the whole weight of an object appears to act for any orientation of the object 25 Consylladated by Lim Ting Jie

26 (f) describe qualitatively the effect of the position of the centre of gravity on the stability of objects Scenario Effect on stability Measure to increase stability Higher centre of gravity Object is tilted such that centre of gravity is still vertically above the base of object Object is tilted such that centre of gravity is no longer vertically above the base of object Lower stability of the object Toppling will occur at smaller angles of tilt Object will not topple Object will topple Decrease the centre of gravity by adding more mass below the current centre of gravity to the object Increase the size of base 26 Consylladated by Lim Ting Jie

27 6. Pressure syllacon.weebly.com Content Pressure Pressure differences Pressure measurement Learning Outcomes Candidates should be able to: (a) define the term pressure in terms of force and area (b) recall and apply the relationship pressure = force / area to new situations or to solve related problems Term Definition Formula SI units Interpretation Pressure Average force per unit area Force Pressure Area F p= A p F A A force of 4 N acting on an area of 2 m 2 results in a pressure of 2 Pa Pa or N m -2 N m 2 (c) describe and explain the transmission of pressure in hydraulic systems with particular reference to the hydraulic press Transmission of pressure in hydraulic systems Description Oil is the incompressible, high density liquid used in the transmission of pressure Effort piston has a smaller cross sectional area than that of the piston below the load Since liquid pressure at both pistons are equal when they are at the same level, A small force exerted on the effort piston will create a much bigger force on the load piston in comparison Diagram Calculations oil Since water level at X is the same as the water level at Y, Pressure at X Pressure at Y FX FY A A F X X Y FY AX AY Since AX AY F F X Y If the load is at Y and F Y represents the weight of the load, use of the hydraulic press will require a smaller force of F X instead of F Y to lift the load upwards 27 Consylladated by Lim Ting Jie

28 (d) recall and apply the relationship pressure due to a liquid column = height of column density of the liquid gravitational field strength to new situations or to solve related problems Term Formula SI units Pressure due to liquid column Pressure due to liquid Height of column Density of liquid Gravitational field strength p hg p h g N m -2 m kg m -3 N kg -1 Example of diagram of manometer gas Calculations Water level at A is the same as the water level at B Gas pressure at A Pressure at B Atmospheric pressure hg at B Pa hg at B (e) describe how the height of a liquid column may be used to measure the atmospheric pressure Diagram of barometer Description of measurement of atmospheric pressure Set up a barometer using high density mercury of 13.6 kg m -3 Atmospheric pressure Pressure from mercury in glass tube hg Pa (f) describe the use of a manometer in the measurement of pressure difference Redirect instructions Refer to Learning Outcome 6(f) above 28 Consylladated by Lim Ting Jie

29 7. Energy, Work and Power syllacon.weebly.com Content Energy conversion and conservation Work Power Learning Outcomes Candidates should be able to: (a) show understanding that kinetic energy, potential energy (chemical, gravitational, elastic), light energy, thermal energy, electrical energy and nuclear energy are examples of different forms of energy Examples of forms of energy Kinetic Potential Thermal Light Electrical Nuclear Movement Stored energy Heat Chemical Gravitational Elastic Food or batteries Raised above ground Compression or stretching of elastic objects like springs (b) state the principle of the conservation of energy and apply the principle to new situations or to solve related problems Term Principle of conservation of energy Definition Energy can neither be created nor destroyed but can only be transferred from one body to another or from one form to another while total energy remains the same (c) calculate the efficiency of an energy conversion using the formula efficiency = energy converted to useful output / total energy input Term Formula Energy input Energy input Useful energy output Wasted energy output Efficiency Useful energy output Efficiency 100% Energy input 29 Consylladated by Lim Ting Jie

30 (d) state that kinetic energy E k = ½ mv 2 and gravitational potential energy E p = mgh (for potential energy changes near the Earth s surface) (e) apply the relationships for kinetic energy and potential energy to new situations or to solve related problems Term Formula SI units Kinetic energy of an object Potential energy of an object Kinetic energy 1 Mass Speed 2 Ek 1 2 mv 2 Gravitational potential energy 2 Mass Gravitational field strength Height Ep mgh E k m v J kg m s -1 E p m g h J kg N kg -1 m (f) recall and apply the relationship work done = force distance moved in the direction of the force to new situations or to solve related problems Term Formula SI units Work done of an object Work done Force Distance travee ll d W Fd W F d J N m (g) recall and apply the relationship power = work done / time taken to new situations or to solve related problems Term Formula SI units Power of an object Work done Energy converted Power Time taken Time taken P = W = E t t P W E t W or J s -1 J J s 30 Consylladated by Lim Ting Jie

31 SECTION III: THERMAL PHYSICS Overview Amongst the early scientists, heat was thought as some kind of invisible, massless fluid called caloric. Certain objects that released heat upon combustion were thought to be able to store the fluid. However, this explanation failed to explain why friction was able to produce heat. In the 1840s, James Prescott Joule used a falling weight to drive an electrical generator that heated a wire immersed in water. This experiment demonstrated that work done by a falling object could be converted to heat. In the previous section, we studied about energy and its conversion. Many energy conversion processes which involve friction will have heat as a product. This section begins with the introduction of the kinetic model of matter. This model is then used to explain and predict the physical properties and changes of matter at the molecular level in relation to heat or thermal energy transfer. Extracted from PHYSICS GCE ORDINARY LEVEL (2014) Syllabus Document 31 Consylladated by Lim Ting Jie

32 8. Kinetic Model of Matter syllacon.weebly.com Content States of matter Brownian motion Kinetic model Learning Outcomes Candidates should be able to: (a) compare the properties of solids, liquids and gases Properties Solids Liquids Gases Volume Fixed Fixed Not fixed Shape Fixed Not fixed Not fixed Compressibility No No Yes Density High High Low Others Usually hard and rigid Tend to form droplets N.A. (b) describe qualitatively the molecular structure of solids, liquids and gases, relating their properties to the forces and distances between molecules and to the motion of the molecules Molecular structure Solids Liquids Gases Forces of attraction between particles Particles held by very strong forces of attraction Particles held by strong forces of attraction Particles held by weak forces of attraction Distance between particles Packed very closely together with more particles per unit volume Packed close to one another Spread far apart from one another Motion of particles Vibrate about fixed positions Slide and move past one another randomly Move in a constant, random and erratic manner (c) infer from Brownian motion experiment the evidence for the movement of molecules Term Definition Brownian motion experiment Setup Observations Inferences Brownian motion Small particles suspended in a liquid or gas tend to move in random paths through the fluid even if it is calm Place smoke particles in a container of air, suspending them in air Smoke particles are being continuously bombarded by air molecules and move irregularly by Brownian motion This shows that the fluids have an ability to flow or move freely 32 Consylladated by Lim Ting Jie

33 (d) describe the relationship between the motion of molecules and temperature syllacon.weebly.com Relationship between motion of molecules and temperature When solid or fluid (liquid / gas) is at a higher temperature, the particles vibrate or move faster respectively The average kinetic energy of the particles is the measure of temperature or degree of hotness (e) explain the pressure of a gas in terms of the motion of its molecules Explanation of pressure of a gas Molecules present in a fluid collide with the walls of the container at a constant rate Each collision exerts a force on the walls of the container As the force is acted on a particular quantity of surface area of walls, the gas exerts pressure on the walls Effect of increasing temperature on pressure When temperature is increased, molecules move faster and collide with the walls of the container more frequently Average force on the walls of the container increases over the same surface area of walls, thus gas pressure increases (f) recall and explain the following relationships using the kinetic model (stating of the corresponding gas laws is not required): (i) a change in pressure of a fixed mass of gas at constant volume is caused by a change in temperature of the gas (ii) a change in volume occupied by a fixed mass of gas at constant pressure is caused by a change in temperature of the gas (iii) a change in pressure of a fixed mass of gas at constant temperature is caused by a change in volume of the gas Gas equation p V p V, where p : Pressure, V : Volume, T : Temperature, only for gases T T 1 2 Cause Temperature of gas increases Volume decreases Effect Volume increases Pressure unchanged Pressure increases Pressure increases Condition Only if container can expand further Only if container can expand further Only if container cannot expand Under all cases Explanation Molecules gain kinetic energy and move faster Gas molecules hit the container walls with higher speed Frequency of collisions of the gas molecules with the walls increases Greater force is exerted on walls, gas expands since container can expand Gas expands in volume since the container can expand, decreasing the number of gas particles per unit volume and increasing surface area of walls Number of gas particles hitting the walls per unit area decreases Average force exerted per unit area remains unchanged, hence a constant pressure is maintained Molecules gain kinetic energy and move faster Gas molecules hit the container walls with higher speed Frequency of collisions of the gas molecules with the walls increases Average force exerted per unit area on the container walls increases Gas is compressed at constant temperature and number of gas particles per unit volume increases Frequency of collisions of molecules with container walls increases Force exerted per unit area on the container increases, thus pressure increases (g) use the relationships in (f) in related situations and to solve problems (a qualitative treatment would suffice) 33 Consylladated by Lim Ting Jie

34 9. Transfer of Thermal Energy syllacon.weebly.com Content Conduction Convection Radiation Learning Outcomes Candidates should be able to: (a) show understanding that thermal energy is transferred from a region of higher temperature to a region of lower temperature Thermal energy transfer Thermal energy is transferred from a region of higher temperature to a region of lower temperature (b) describe, in molecular terms, how energy transfer occurs in solids Energy transfer occurs in solids When one region of a solid is heated, the molecules there gain kinetic energy and vibrate faster They collide with the slower neighbouring particles and transfer energy to them In comparison with fluids In fluids, the particles are further apart from each another than in liquids or gases Therefore kinetic energy is transferred more slowly (c) describe, in terms of density changes, convection in fluids Convection in fluids Hot fluid expands and has lower density than cold fluid, causing it to rise Cold fluid contracts and has higher density than hot fluids, sinking to replace the hot fluid Convection current is set up when the cycle repeats In comparison with solids Convection involves the bulk movement of fluids which carry heat with them Solids cannot cause convection as heat can only be transferred from one molecule to another The molecules are unable to flow around themselves (d) explain that energy transfer of a body by radiation does not require a material medium and the rate of energy transfer is affected by: (i) colour and texture of the surface (ii) surface temperature (iii) surface area Energy transfer of a body by radiation Infrared radiation is continuously emitted by all objects through their surfaces as radiation does not require a material medium for thermal transfer to occur When these infrared waves reach another object, the waves are transformed into heat energy, which is then absorbed by the object Higher surface areas, higher surface temperatures (relative to surroundings) and dull surfaces accelerate radiation of heat 34 Consylladated by Lim Ting Jie

35 (e) apply the concept of thermal energy transfer to everyday applications syllacon.weebly.com Applications Features Advantages Reasons Styrofoam food packages Mostly made of styrofoam Covered with a lid Conduction is reduced Convection is reduced This is due to the presence of many air pockets Air is a poor conductor of heat Convection currents are unable to be set up due to the presence of the lid compressing the contents into a closely packed arrangement Vacuum flasks Plastic stopper Conduction & convection is reduced Plastic is a poor conductor of heat With a stopper, a convection current is being prevented from set up Vacuum between the glass walls As vacuum is unable to conduct and cause convection of heat, the amount of heat medium is decreased Silvered glass walls Radiation is reduced The shiny and smooth surface is a poor emitter and absorber of heat It is able to reflect heat back to the container very well Air trapped above contents Conduction is reduced Air is a poor conductor of heat 35 Consylladated by Lim Ting Jie

36 10. Temperature syllacon.weebly.com Content Principles of thermometry Learning Outcomes Candidates should be able to: (a) explain how a physical property which varies with temperature, such as volume of liquid column, resistance of metal wire and electromotive force (e.m.f.) produced by junctions formed with wires of two different metals, may be used to define temperature scales Differences Mercury thermometer Platinum wire Thermocouple Physical property Volume or height of liquid column Resistance Electromotive force (e.m.f.) produced by 2 junctions formed with wires of 2 different metals Rationale Mercury is sensitive to changes in temperature and expands when temperature rises Resistance of the wire rises when temperature rises Voltage Resistance Current E.m.f. between two substances increases when the temperature difference between them rises Apparatus Copper mv Iron Copper 0 o C Calculations where is the value of physical property used (can be ve / ve) o C X 0 100, X X X X and o C is the temperature of the substance measured (b) describe the process of calibration of a liquid-in-glass thermometer, including the need for fixed points such as the ice point and steam point Calibration of liquid-in-glass thermometer Place thermometer in ice point (funnel containing pure melting ice), then in steam point (above boiling water) Mark the level of mercury in both situations The difference in temperature of both points is 100 o C Between the upper and lower fixed points markings, divide and mark one hundred equal divisions Since an increase in the temperature will increase the volume of mercury proportionately, each division is one degree Celsius Need for fixed points Fixed points (ice and steam points) are used for calibration for all thermometers to agree accurately on a same temperature scale This is because fixed points are reproducible and will produce definite temperatures 36 Consylladated by Lim Ting Jie

37 11. Thermal Properties of Matter syllacon.weebly.com Content Internal energy Specific heat capacity Melting, boiling and evaporation Specific latent heat Learning Outcomes Candidates should be able to: (a) describe a rise in temperature of a body in terms of an increase in its internal energy (random thermal energy) Term Internal energy Meaning Random thermal energy of a body resulting from the kinetic and potential energy of the particles by their movement and arrangement Description of rise in temperature of a body When a body is heated, its internal energy (consisting of kinetic energy and potential energy) rises Kinetic energy Kinetic energy of particles increases, causing particles vibrate or move faster Potential energy During melting and boiling, potential energy of the particles also increases This is since there is no rise in temperature, causing latent heat to be taken in (b) define the terms heat capacity and specific heat capacity Term Definition Symbol Heat capacity Amount of heat energy required to raise the temperature of a body by 1 K or 1 C C Specific heat capacity Amount of heat energy required to raise the temperature of 1 kg of a body by 1 K or 1 C c (c) recall and apply the relationship thermal energy = mass specific heat capacity change in temperature to new situations or to solve related problems Term Formula SI units Thermal energy when there is a temperature change Thermal energy Mass Specific heat capacity Change in temperature Heat ( m)( c)( ) m c kg J kg -1 o C -1 or J kg -1 K -1 o C or K 37 Consylladated by Lim Ting Jie

38 (d) describe melting/solidification and boiling/condensation as processes of energy transfer without a change in temperature Term Melting Solidification Boiling Condensation Meaning Process of energy transfer from the surroundings to a solid to turn it to a liquid without a change in temperature Process of energy transfer from a liquid to the surroundings to turn it to a solid without a change in temperature Process of energy transfer from the surroundings to a liquid to turn it to a gas without a change in temperature Process of energy transfer from a gas to the surroundings to turn it to a liquid without a change in temperature (e) explain the difference between boiling and evaporation Description of evaporation At any temperature, the molecules of liquid are in continuous random motion with different speeds Some more energetic molecules near to the surface of the liquid have enough energy to overcome the attractive forces of other molecules and escape They evaporate from the liquid to form a vapour Differences Boiling Evaporation Temperature Occurs at a fixed temperature Occurs at any temperature Location Occurs throughout the liquid Occurs at the surface of the liquid Heat source Heat is supplied from an energy source Heat is supplied by the surroundings (f) define the terms latent heat and specific latent heat Latent heat Term Latent heat of fusion Latent heat of vapourisation Specific latent heat Definition Heat energy released or absorbed during a change of state to make or break intermolecular forces of attraction without any change in temperature Heat energy required to change a solid to its liquid state or vice versa without any change in temperature Heat energy required to change a liquid to its vapour state or vice versa without any change in temperature Heat energy required to change 1 kg of a substance from one state to another or vice versa (g) recall and apply the relationship thermal energy = mass specific latent heat to new situations or to solve related problems Term Formula SI units Thermal energy when there is no temperature change Thermal energy Mass Specific latent heat Latent heat ( m)( ) f m kg J kg -1 f 38 Consylladated by Lim Ting Jie

39 (h) explain latent heat in terms of molecular behaviour Term Latent heat Definition Heat energy released or absorbed during a change of state to make or break intermolecular forces of attraction without any change in temperature (i) sketch and interpret a cooling curve Sketch of cooling curve of water Interpretation of cooling curve condensation Description Decreases in temperature during gas, liquid and solid state in the graph No change in temperature during condensation and freezing until all the water vapour has condensed and all the water has frozen Explanation This is because thermal energy is being released with no change in intermolecular forces of attraction between the molecules This is because thermal energy is being released to form greater intermolecular forces of attraction between the molecules such that there is a state change 39 Consylladated by Lim Ting Jie

40 SECTION IV: WAVES Overview Waves are inherent in our everyday lives. Much of our understanding of wave phenomena has been accumulated over the centuries through the study of light (optics) and sound (acoustics). The nature of oscillations in light was only understood when James Clerk Maxwell, in his unification of electricity, magnetism and electromagnetic waves, stated that all electromagnetic fields spread in the form of waves. Using a mathematical model (Maxwell s equations), he calculated the speed of electromagnetic waves and found it to be close to the speed of light, leading him to make a bold but correct inference that light consists of propagating electromagnetic disturbances. This gave the very nature of electromagnetic waves, and hence its name. In this section, we examine the nature of waves in terms of the coordinated movement of particles. The discussion moves on to wave propagation and its uses by studying the properties of light, electromagnetic waves and sound, as well as their applications in wireless communication, home appliances, medicine and industry. Extracted from PHYSICS GCE ORDINARY LEVEL (2014) Syllabus Document 40 Consylladated by Lim Ting Jie

41 12. General Wave Properties syllacon.weebly.com Content Describing wave motion Wave terms Longitudinal and transverse waves Learning Outcomes Candidates should be able to: (a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs and by waves in a ripple tank Term Wave motion Definition Propagation of waves through a medium by the vibration of particles in the wave transmitting energy Illustrations Transverse waves Longitudinal waves Rope N.A. Spring Ripple tank N.A. 41 Consylladated by Lim Ting Jie

42 Comparison of waves in a ripple tank Description Waves of water undergo refraction when it travels from deeper water to shallower water or vice versa Differences Deeper water Shallower water Illustrations Wavelength Increases Decreases Velocity Increases Decreases Frequency Remains the same Remains the same Direction Away from the normal Towards the normal Wavefront Perpendicular to direction of wave Perpendicular to direction of wave (b) show understanding that waves transfer energy without transferring matter Waves A wave is the collective motion of many particles Occurs when particles of the medium move in a specific manner What is transferred Energy What is not transferred Medium (c) define speed, frequency, wavelength, period and amplitude Term Definition Formula Frequency The number of complete waves produced per second by a source 1 f T Period The time taken to produce one complete wave 1 T f Wavelength Shortest distance between any two points of a wave in phase Represented by Speed Distance travelled by a crest or rarefraction per unit time by a wave v f (Refer to diagram) Amplitude Maximum displacement of crest or rarefaction from the rest position Refer to diagram Diagram 42 Consylladated by Lim Ting Jie

43 (d) state what is meant by the term wavefront Term Wavefront Definition Imaginary line on a wave that joins all points that are in the same phase (e) recall and apply the relationship velocity = frequency wavelength to new situations or to solve related problems Term Formula SI units Velocity of wave Velocity Frequency Wavelength v f v f m s -1 Hz m (f) compare transverse and longitudinal waves and give suitable examples of each Term Definition Properties Transverse wave Longitudinal wave Waves that travel in a direction perpendicular to the direction of vibration of the particles Waves that travel in a direction parallel to the direction of vibration of the particles Crests and troughs represent amplitude and minimum displacement respectively Rarefactions and compressions represent amplitude and minimum displacement respectively 43 Consylladated by Lim Ting Jie

44 13. Light syllacon.weebly.com Content Reflection of light Refraction of light Thin lenses Learning Outcomes Candidates should be able to: (a) recall and use the terms for reflection, including normal, angle of incidence and angle of reflection Ray diagram mirror Legend i represents the angle of incidence r represents the angle of reflection (b) state that, for reflection, the angle of incidence is equal to the angle of reflection and use this principle in constructions, measurements and calculations Reflection laws Angle of incidence is equal to angle of reflection The normal, incident ray and reflected ray all lie in the same plane Features of a plane mirror image Features Virtual Image is the same size as the object (Size) Image as far away from the mirror as the object is from the mirror (Far) Laterally inverted Upright Acronym VS FLU 44 Consylladated by Lim Ting Jie

45 (c) recall and use the terms for refraction, including normal, angle of incidence and angle of refraction Term Meaning Conditions Remark Refraction Refers to the change in direction or bending of light when it passes from one medium to another medium of different optical densities due to the change in speed of light The light ray bends towards the normal when travelling into a medium of higher optical density The light ray bends away from the normal when travelling into a medium of lower optical density Angle of incidence must not be 0 o If ray travels from a denser to less dense medium, angle of incidence must be less than critical angle Density in this case represents optical density Ray diagram Real and apparent depth Legend i represents the angle of incidence r represents the angle of refraction (d) recall and apply the relationship sin i / sin r = constant to new situations or to solve related problems (e) define refractive index of a medium in terms of the ratio of speed of light in vacuum and in the medium Term Definition Formula Legend Refractive index of a medium The constant ratio of the speed of light in vacuum to the speed of light in the medium Speed of light in vacuum n Speed of light in medium sin i (from vacuum to medium) sin r sin r (from medium to vacuum) sin i Real depth Apparent depth n represents refractive index i represents the angle of incidence r represents the angle of refraction 45 Consylladated by Lim Ting Jie

46 (f) explain the terms critical angle and total internal reflection Term Definition Formula Critical angle Total internal reflection The angle of incidence of a ray in the optically denser medium whereby the angle of refraction of it in the optically less dense medium is 90 o Reflection of light rays within the optically denser medium when the angle of incidence in the optically denser medium is more than the critical angle -1 1 sin 90 1 c sin, n n sin c sin c N.A. Illustrative diagrams Refraction Critical angle Total internal reflection i represents the angle of incidence which is less than critical angle r represents the angle of refraction which is within the optically less dense medium and is less than 90 o i represents the angle of incidence which is equal to critical angle r represents the angle of refraction which is along the boundary of the 2 mediums and is equal to 90 o i represents the angle of incidence which is more than critical angle r represents the angle of reflection which is within the optically denser medium and is equal to 90 o (g) identify the main ideas in total internal reflection and apply them to the use of optical fibres in telecommunication and state the advantages of their use Main ideas in total internal reflection Light ray has to travel from denser medium towards the less dense medium Angle of incidence of light ray is more than critical angle The light ray will reflect internally by the laws of reflection within the denser medium Optical fibres in telecommunications Advantages Diagram Light pulses carry telecommunications data at a faster rate Less data loss compared to use of copper wires Optical fibres are generally cheaper and lighter than copper wires 46 Consylladated by Lim Ting Jie

47 (h) describe the action of a thin lens (both converging and diverging) on a beam of light Differences Converging lens Diverging lens Lens type Convex lens Concave lens Light rays Ray diagram optical center principal focus Description of lens action The lens is curved, thus the angles of incidence of parallel rays of light differ, causing the rays to change direction differently after passing through the lens The front of the lens facing the incident light rays curve outwards The light rays converge at a common focal point The lens is curved, thus the angles of incidence of parallel rays of light differ, causing the rays to change direction differently after passing through the lens The front of the lens facing the incident light rays curve inwards The light rays diverge from one another (i) define the term focal length for a converging lens Term Definition Diagram Focal length of converging lens Distance between the optical center and the principal focus, where parallel rays of light converge after passing through the lens focal length 47 Consylladated by Lim Ting Jie

48 (j) draw ray diagrams to illustrate the formation of real and virtual images of an object by a thin converging lens # Object location Image location Image properties Acroynm Uses 1 u v f Diminished, inverted, real DIR Telescope 2 u 2f 2f v f Diminished, inverted, real DIR Camera Eye 3 u 2f v 2f Same size, inverted, real SIR Photocopier 4 2f u f v 2f Magnified, inverted, real MIR Projector 5 u f v Magnified, upright, virtual MUV Spotlight 6 u f f v 2f Magnified, upright, virtual MUV Magnifying glass Spectacles Image formation based on object location # 1 2 Object location u u 2f Ray diagram # 3 4 Object location u 2f 2f u f Ray diagram # 5 6 Object location u f u f Ray diagram 48 Consylladated by Lim Ting Jie

49 14. Electromagnetic Spectrum syllacon.weebly.com Content Properties of electromagnetic waves Applications of electromagnetic waves Effects of electromagnetic waves on cells and tissue Learning Outcomes Candidates should be able to: (a) state that all electromagnetic waves are transverse waves that travel with the same speed in vacuum and state the magnitude of this speed # Point Property of electromagnetic waves (EM waves) 1 Type Transverse waves Electric and magnetic fields oscillate 90 o to each other 2 Laws They obey the laws of reflection and refraction 3 Electric charge No electric charge is carried through EM waves 4 Medium No medium is required and the wave can travel through vacuum 5 Frequency Remains the same all the time 6 Wavelength Decreases from optically less dense to denser medium 7 Velocity 3 x 10 8 ms -1 in vacuum, slows down in matter Decreases from optically less dense to denser medium 49 Consylladated by Lim Ting Jie

50 (b) describe the main components of the electromagnetic spectrum (c) state examples of the use of the following components: (i) radiowaves (e.g. radio and television communication) (ii) microwaves (e.g. microwave oven and satellite television) (iii) infra-red (e.g. infra-red remote controllers and intruder alarms) (iv) light (e.g. optical fibres for medical uses and telecommunications) (v) ultra-violet (e.g. sunbeds and sterilisation) (vi) X- rays (e.g. radiological and engineering applications) (vii) gamma rays (e.g. medical treatment) Component Frequency Applications Description Radio waves 1 10^ 8 Hz Radio and television communications Able to go around obstructions (due to longer wavelengths) Microwaves 1 10^ 10 Hz Microwave oven Water molecules vibrate millions of times a second to produce heat from friction Satellite television Can penetrate haze, light rain, snow, clouds and smoke with proper alignment Infra-red 1 10^ 12 Hz Remote controllers Intruder alarms Alarm rings when it receives infra-red radiation an intruding human gives out Light (Red) 5 10^ 14 Hz Medical optical fibres (Violet) Telecommunications Ultra-violet 3 10^ 16 Hz Sunbeds Artificial tanning (shorter frequency UVA) X-rays Sterilisation 3 10^ 18 Hz Diagnose fractures Airport scanners Germicidal lamps (longer frequency UVB/C) Can penetrate through all materials other than lead, thus may be applied using X-ray imagery Gamma rays 3 10^ 20 Hz Cancer treatment Kill cancer cells in cancerous tumours (high energy waves) Changes in the EM spectrum from radio to gamma waves Frequency Increases from radio waves to gamma rays Wavelength Decreases from radio waves to gamma rays (d) describe the effects of absorbing electromagnetic waves, e.g. heating, ionisation and damage to living cells and tissue Effects of absorbing electromagnetic waves Infrared High energy EM waves X-rays Human skin absorbs infrared waves from BBQ pits Human bodies will receive the radiation and be heated to feel warm EM waves of frequencies higher than light have high energy causing ionisation Ionisation of living matter in human bodies damages chromosomes, living cells and tissues Overexposure leads to premature ageing and lifespan shortening Overexposure of developing fetus to X- ray imagery can cause abnormal cell division A deformed baby and leukemia may result 50 Consylladated by Lim Ting Jie

51 15. Sound syllacon.weebly.com Content Sound waves Speed of sound Echo Ultrasound Learning Outcomes Candidates should be able to: (a) describe the production of sound by vibrating sources (b) describe the longitudinal nature of sound waves in terms of the processes of compression and rarefaction Production of sound in air A vibrating source causes particles in air to be displaced, moving away and from the source continuously Description of sound waves Air particles oscillate left and right to produce compressions at high air pressure and rarefactions at low air pressure A longitudinal sound wave is produced (c) explain that a medium is required in order to transmit sound waves and the speed of sound differs in air, liquids and solids Conditions for transmission of sound waves A vibrating source must be present The source must be placed in a medium Energy transmitted by sound waves depends on its frequency and amplitude Speed of sound increases from gas to solid Approximate speeds of sound In gases Air 330 m s -1 In liquids Water 1500 m s -1 In solids Iron 5000 m s -1 Steel 6000 m s -1 (d) describe a direct method for the determination of the speed of sound in air and make the necessary calculation Experiment to determine speed of sound in air Method Calculation Reliability Observers A and B are positioned at a far distance apart, S, to minimise human reaction error Observer A fires a pistol and Observer B starts the stopwatch on seeing the flash of the pistol He stops the stopwatch when he hears the sound The time interval between the two actions, T, is recorded Speed of sound is calculated by the following formula: Speed S T For better accuracy, the experiment is repeated and the average speed of sound is calculated The experiment is further repeated by interchanging the positions of Observers A and B to minimise the effects of wind 51 Consylladated by Lim Ting Jie

52 (e) relate loudness of a sound wave to its amplitude and pitch to its frequency syllacon.weebly.com Cause Frequency increases Amplitude increases Effects on Pitch Increases Remains the same Loudness Remains the same Increases (f) describe how the reflection of sound may produce an echo, and how this may be used for measuring distances Experiment to measure distances using echoes Theory Method Calculation Reliability Sound waves follow the laws of reflectlon The harder and larger the surface is, the stronger the echo When sound waves are reflected after striking objects, the reflected sound, an echo, is produced When a source emits a sound and then receives an echo, the sound must have travelled a distance of 2D, where D is the distance between the source and the reflected surface The time interval between emission and receiving of the sound is recorded as T The speed of sound in the medium is labelled as V Distance from source and reflected surface is calculated by the following formula: TV D 2 For better accuracy, the experiment is repeated and the average distance is calculated Example of measuring distances using echoes (depth of seabed) Diagram Calculation Let 2d be the depth of the seabed, T be the duration between sound emission and echo receival, and V be the speed of sound in water, which is 1500 ms Total distance travelled by sound 2d TV TV 1500T d 750T (g) define ultrasound and describe one use of ultrasound, e.g. quality control and pre-natal scanning Term Definition Uses Description Mechanism Ultrasound Sound with waves above 20 khz frequency, which is above the upper limit of the human hearing range Quality control Manufactures of various concrete types check for cracks or cavities in concrete slabs with ultrasound to ensure that their concrete are of the highest quality Ultrasound is released from an emitter at one end of the concrete slab and a sensor is positioned at the other end to detect the ultrasound If the speed of sound recorded is lower than actual, this means parts of the concrete contain air (Humans can only hear sound of frequencies between 20 Hz to 20 khz) Pre-natal scanning Ultrasound can be used to obtain images of inside a body, thus is used to examine development of a foetus in a pregnant woman Ultrasound pulses are sent into the body using a trasmitter Echoes reflected from any surface within the body are received The time interval is noted to determine the depth of the reflecting surface within the body 52 Consylladated by Lim Ting Jie

53 SECTION V: ELECTRICITY AND MAGNETISM Overview For a long time, electricity and magnetism were seen as independent phenomena. Hans Christian Oersted, in 1802, discovered that a current carrying conductor deflected a compass needle. This discovery was overlooked by the scientific community until 18 years later. It may be a chance discovery, but it takes an observant scientist to notice. The exact relationship between an electric current and the magnetic field it produced was deduced mainly through the work of Andre Marie Ampere. However, the major discoveries in electromagnetism were made by two of the greatest names in physics, Michael Faraday and James Clerk Maxwell. The section begins with a discussion of electric charges that are static, i.e. not moving. Next, we study the phenomena associated with moving charges and the concepts of current, voltage and resistance. We also study how these concepts are applied to simple circuits and household electricity. Thereafter, we study the interaction of magnetic fields to pave the way for the study of the interrelationship between electricity and magnetism. The phenomenon in which a current interacts with a magnetic field is studied in electromagnetism, while the phenomenon in which a current or electromotive force is induced in a moving conductor within a magnetic field is studied in electromagnetic induction. Extracted from CHEMISTRY GCE ORDINARY LEVEL (2014) Syllabus Document 53 Consylladated by Lim Ting Jie

54 16. Static Electricity syllacon.weebly.com Content Laws of electrostatics Principles of electrostatics Electric field Applications of electrostatics Learning Outcomes Candidates should be able to: (a) state that there are positive and negative charges and that charge is measured in coulombs Charge Types Positive Negative Measurement Charge is measured in coulombs (C) For example, one negative electron has a charge of 1.6 x C (b) state that unlike charges attract and like charges repel Interaction of charges Combination of charges Interaction Unlike charges Positive-negative Attract Like charges Positive-positive Repel Negative-negative (c) describe an electric field as a region in which an electric charge experiences a force (d) draw the electric field of an isolated point charge and recall that the direction of the field lines gives the direction of the force acting on a positive test charge Term Electric field Electric field lines Definition Region in which an electric charge experiences a force Gives direction of the electric field (i.e. direction of the force on a small positive charge) Electric field of an isolated point charge Diagram Positive charge Negative charge Field lines From charge Towards charge 54 Consylladated by Lim Ting Jie

55 (e) draw the electric field pattern between two isolated point charges Electric field of an isolated point charge Positive-negative Positive-positive Negative-negative Opposite charges attract, hence the two charges are linked by field lines Like charges repel, hence no field lines connect the two charges Electric field of parallel charged plates (f) show understanding that electrostatic charging by rubbing involves a transfer of electrons Experimental method of rubbing (to show electrostatic charging between 2 uncharged materials) Action Rub two different materials against each other Result Some negatively charged electrons are transferred from one material to the other An object becomes negatively charged if it gains electrons and positively charged if it loses electrons Ease of loss of electrons between objects Ease of loss of electrons generally decreases down the following list: Electron loss Object type Examples Electron transfer Easiest Transparent object Glass, Perspex Smooth, high surface area object Silk, Fur, Hair, Wool Hardest Opaque object Ebonite, Rubber, Polyethene 55 Consylladated by Lim Ting Jie

56 (g) describe experiments to show electrostatic charging by induction Experimental method of induction (to show electrostatic charging of a single metal conductor) # Action Result Diagram 1 To negatively charge a neutral conductor, bring a positively charged rod near it 2 Earth the side of the conductor with the positive charges 3 Remove the Earth, then the rod Like charges repel and unlike charges attract each other Thus the positively charged rod leaves an excess of negative charges at the side of conductor nearest to the rod and positive charges at the other side by induction Electrons flow from Earth to the conductor to neutralise the positive charges Electron migration causes the rod to be completely negatively charged Experimental method of induction (to show electrostatic charging of 2 metal spheres) # Action Result 1 Let the two conductors (metal spheres on insulating stands) touch each other Bring a negatively charged rod near the conductor on the left The negatively charged rod induces the charges in the two conductors, repelling the negative charges to the furthest end of the conductor on the right, leaving excess positive charges at the end of conductor on the left nearest to the rod 2 Separate the two conductors far from each other Remove the rod The conductor on the left will be positively charged while the other on the right will be negatively charged (h) describe examples where electrostatic charging may be a potential hazard Potential hazards of electrostatic charging Lightning Friction between water molecules in thunderclouds and air molecules in the air cause the thunderclouds to be charged Air is ionised when the charge on the thunderclouds becomes large enough The ionised air provides a conducting path for the huge quantity of electric charge on the thunderclouds to the nearest object or sharpest object on the ground via lightning strikes during a sudden discharge Electrostatic charging is thus a potential hazard for people when they are out in an open field or under a tall tree during a thunderstorm, especially in the absence of a lightning conductor Electrostatic discharge Friction between objects may cause excessive charges to build up in them: Friction between tyres of a truck and the road can result in sudden discharge Sparks and subsequent ignition of flammable items on the truck may occur when this happens Friction between electronic equipment (e.g. computer boards, hard drives) and other objects can result in electrostatic discharges over time These electronic equipment may be damaged as this happens 56 Consylladated by Lim Ting Jie

57 (i) describe the use of electrostatic charging in a photocopier, and apply the use of electrostatic charging to new situations Components of the photocopier Photoreceptor drum Laser assembly Toner Fuser Metal drum roller Coated with a photoconductive layer Laser Movable mirror Lens Fine negatively charged powder Heat source Electrostatic charging in a photocopier # Action Result Diagram 1 A photoreceptor drum is rotated near a highly positively charged corona wire The photoreceptor drum becomes positively charged 2 The laser beam is cast over a page of the original document through a lens onto the photoreceptor drum Areas of photoconductive layer on the drum surface that are exposed to the laser is discharged Negatively charged toner is then attracted to the remaining positively charged areas 3 Toner on the drum is transferred to the paper Paper is heated by the fuser Toner power melts onto the paper surface, affixing itself permanently on the surface Note: A laser printer operates differently from a photocopier, although both rely on electrostatic charging 57 Consylladated by Lim Ting Jie

58 17. Current of Electricity syllacon.weebly.com Content Conventional current and electron flow Electromotive force Potential difference Resistance Learning Outcomes Candidates should be able to: (a) state that current is a rate of flow of charge and that it is measured in amperes Term Definition Measurement Formula SI units Curren t A measure of the rate of flow of electric charge through a cross section of a conductor Ammeter Connected in series Charge Current Time I Q t Q I t A C s (b) distinguish between conventional current and electron flow Conventional current flow Electron flow Combined flow of charges Flow of positive charges from a positively charged end to a negatively charged end (i.e. current) Flow of electrons from a negatively charged end to a positively charged end (c) recall and apply the relationship charge = current time to new situations or to solve related problems Term Definition Formula SI units Charge When an object is charged, it is electrified Equals to the product of current and time Charge Current Time Q It Q I t C A s 58 Consylladated by Lim Ting Jie

59 (d) define electromotive force (e.m.f.) as the work done by a source in driving unit charge around a complete circuit Term Definition Measurement Formula SI units Electromotive force Work done by an electrical source in driving a unit charge round a complete circuit Voltmeter Connected in parallel across the positive and negative ends of the electrical source E.m.f. Electrical energy converted Charge W Q W Q V J C (e) calculate the total e.m.f. where several sources are arranged in series Example of circuit of 3 dry cells as sources Diagram Readings recorded Total e.m.f. Voltmeter Dry cell e.m.f. Total e.m.f. of all dry cells V Sum of all e.m.f. of each dry cell V V 3 3 V (f) state that the e.m.f. of a source and the potential difference (p.d.) across a circuit component is measured in volts (g) define the p.d. across a component in a circuit as the work done to drive unit charge through the component Term Definition Measurement Formula SI units Potential difference Amount of energy converted to other forms of energy when one coulomb of positive charge passes between 2 reference points Voltmeter Connected in parallel across the 2 points Potential difference Electrical energy converted Charge W V Q Q t A C s (h) state the definition that resistance = p.d. / current (i) apply the relationship R = V/I to new situations or to solve related problems Term Definition Factors Formula 1 SI units Resistance Ratio of the potential difference across a component to the current flowing through it Length Cross sectional area Type of material Potential difference Resistance Current V R I R V I Ω or ohm V A 59 Consylladated by Lim Ting Jie

60 (j) describe an experiment to determine the resistance of a metallic conductor using a voltmeter and an ammeter, and make the necessary calculations Experiment to determine resistance of a metallic conductor Method Connect a dry cell, rheostat and ammeter in series to the metallic conductor In the same circuit, connect a voltmeter in parallel to the metallic conductor Vary the resistance of the rheostat and and note down values of V (reading of voltmeter) and I (reading of ammeter) for at least 5 sets of readings Calculation By Ohm s law, resistance R will be equivalent to the voltage divided by current V R I Hence, plot a graph of V against I to find the gradient of the graph, R (k) recall and apply the formulae for the effective resistance of a number of resistors in series and in parallel to new situations or to solve related problems Differences Resistors in series Resistors in parallel Circuit diagram where R 1 and R 2 are the resistances of the resistors respectively where R 1 and R 2 are the resistances of the resistors respectively Formula for effective resistance for the circuit above R R R eff R R R eff R eff R R Nature of effective resistance R R eff eff R 1 R 2 R R eff eff R 1 R 2 General formula for effective resistance Reff R1... R 1 n 1 1 Reff... R1 Rn 60 Consylladated by Lim Ting Jie

61 (l) recall and apply the relationship of the proportionality between resistance and the length and cross-sectional area of a wire to new situations or to solve related problems Differences Resistance of material Resistivity of material Main formula V R I RA l Unit Ω Ω m Nature Resistance increases as length increases Resistance increases as cross-sectional area decreases Independent of length & crosssectional area Term Formula 2 SI units Relationships Resistance Wire length Resistance Resistivity Cross-sectional area R l A R l A R l 1 R Ω Ω m m m 2 A (m) state Ohm s Law Law Definition Relationship Ohm s Law Current passing through a metallic conductor is directly proportional to the potential difference across its ends, provided the physical conditions are constant I V V R constant I (n) describe the effect of temperature increase on the resistance of a metallic conductor Effect of temperature increase on resistance Resistance of metallic conductor increases Explanation Particles in metallic conductor gain kinetic energy and vibrate faster This causes electrons moving through the conductor to slow down 61 Consylladated by Lim Ting Jie

62 (o) sketch and interpret the I/V characteristic graphs for a metallic conductor at constant temperature, for a filament lamp and for a semiconductor diode Differences Ohmic conductors Filament lamp Non-ohmic conductors (examples) Semiconductor diode Purpose N.A. Provides light indoors and at night Allows current to flow in only one direction (i.e. forward direction) through the circuit I/V sketch V/I sketch (invert the I/V sketch along the line V=I) Interpretation Ohmic conductors follow Ohm s law The filament lamp is a non-ohmic conductor The semiconductor diode is another nonohmic conductor Gradient V/I is constant since I is directly proportional to V Gradient V/I increases as V increases across the lamp This is because as p.d. increases, the current increases less than proportionately This indicates that resistance of the lamp increases as p.d. increases Gradient V/I decreases as V increases from zero This is because as p.d. increases, the current increases more than proportionately This indicates that resistance decreases when p.d. in the forward direction increases, allowing a relatively large current, I, to flow through Gradient V/I is very large as V increases to zero This indicates that resistance is very high when p.d. in the reverse direction increases Almost no current flows in this reverse direction 62 Consylladated by Lim Ting Jie

63 18. D.C. Circuits syllacon.weebly.com Content Current and potential difference in circuits Series and parallel circuits Potential divider circuit Thermistor and light-dependent resistor Learning Outcomes Candidates should be able to: (a) draw circuit diagrams with power sources (cell, battery, d.c. supply or a.c. supply), switches, lamps, resistors (fixed and variable), variable potential divider (potentiometer), fuses, ammeters and voltmeters, bells, light-dependent resistors, thermistors and lightemitting diodes Symbols of power sources Symbols of common components Cell Battery D.C supply A.C. supply Lamp Bell Switch Fuse Symbols of resistors and diodes Fixed resistor Variable resistor Thermistor Light-dependent resistor Light-emitting diode Symbols of measurement devices Symbols of other devices Ammeter Voltmeter Potentiometer Circuit diagram example Experimental setup Circuit diagram 63 Consylladated by Lim Ting Jie

64 (b) state that the current at every point in a series circuit is the same and apply the principle to new situations or to solve related problems (c) state that the sum of the potential differences in a series circuit is equal to the potential difference across the whole circuit and apply the principle to new situations or to solve related problems (d) state that the current from the source is the sum of the currents in the separate branches of a parallel circuit and apply the principle to new situations or to solve related problems (e) state that the potential difference across the separate branches of a parallel circuit is the same and apply the principle to new situations or to solve related problems Circuit Current in circuit Potential difference across whole circuit Series Same at every point Sum of potential differences in circuit Parallel Sum of currents in the separate branches Same as across the separate branches (f) recall and apply the relevant relationships, including R = V/I and those for current, potential differences and resistors in series and in parallel circuits, in calculations involving a whole circuit Term Formula SI units Remarks Resistance Potential difference Resistance Current V R I R Ω or ohm V V I A When the circuit has resistors in both the series and parallel arrangement, calculate effective resistance of the ones arranged in parallel first (g) describe the action of a variable potential divider (potentiometer) Purpose of potentiometer A potentiometer is able to divide the supply voltage in any ratio that is required by varying resistance and using the formula V IR Action of potentiometer The potentiometer is made of a conducting slider in contact with a resistor with fixed cross-sectional area By sliding the slider along the resistor, the length of the resistance material that the current of the circuit has to flow through can be varied Since R l, resistance of the circuit increases when the length increases As V IR, potential difference across the circuit can thus be adjusted between zero and the maximum supply voltage (h) describe the action of thermistors and light-dependent resistors and explain their use as input transducers in potential dividers (i) solve simple circuit problems involving thermistors and light-dependent resistors Input tranducers Transducers that convert non-electrical energy to electrical energy Differences Thermistor Light-dependent resistor Device Applications A device whose resistance decreases when temperature increases Temperature control Temperature measurement in fire alarms A device whose resistance decreases as the amount of light shining on it increases Under bright lighting, the LDR would have very low resistance, and vice versa 64 Consylladated by Lim Ting Jie

65 19. Practical Electricity syllacon.weebly.com Content Electric power and energy Dangers of electricity Safe use of electricity in the home Learning Outcomes Candidates should be able to: (a) describe the use of the heating effect of electricity in appliances such as electric kettles, ovens and heaters Use of electricity Heating effect Used in heating appliances like electric kettles, ovens and heaters Description of use Heating elements in heating appliances musthave high resistivity (high resistance per unit length of material of constant cross-sectional area) and must be able to withstand high temperatures When current passes through these elements (e.g. nichrome) in heating appliances when, much heat is generated By varying current passing through, heat produced by Joule heating can be effectively controlled (b) recall and apply the relationships P = VI and E = VIt to new situations or to solve related problems Term Formula SI units Derivation of formulae Electrical energy Energy Current Voltage Time E VIt Electrical power Power Current Voltage P VI E V I t P VI is derived from: J V A s Q I Q It t P V I W V W VQ VIt Q W V A W VQ VIt P VI t t t (c) calculate the cost of using electrical appliances where the energy unit is the kw h Term Formula SI units Electrical energy Energy Power Time E Pt E P t kwh kw h Cost of using electrical appliances Cost Energy Rate Cost Energy Rate kwh per kwh 65 Consylladated by Lim Ting Jie

66 (d) compare the use of non-renewable and renewable energy sources such as fossil fuels, nuclear energy, solar energy, wind energy and hydroelectric generation to generate electricity in terms of energy conversion efficiency, cost per kw h produced and environmental impact Energy source Renewability Energy conversion Source Efficiency Reasons Fossil fuels Nonrenewable Chemical potential energy 30-40% Good distribution system of electricity from fossil fuels in many countries Nuclear energy Nonrenewable Nuclear energy 30-40% Only a small amount of uranium is needed to generate a large amount of energy Solar energy Renewable Light energy 10-20% Efficiency is high only when there is daylight and minimal cloud cover Wind energy Renewable Kinetic energy 30-40% Wind direction and speed varies Hydroelectric generation Renewable Gravitational potential energy 90% Water flow is concentrated can be easily controlled Non-renewable energy sources Energy source Cost per kwh produced Environmental impact Fossil fuels Nuclear energy High costs due to lower availability of fossils higher energy demand Radioactivity, when leaked, is very expensive to clean up Gases produced as a result of the combustion of fossil fuels are usually pollutive (e.g. may combine with rain to form acid rain) Radioactivity, when leaked, is difficult and expensive to clean up Threat to safety as it can cause mutations to humans Non-renewable energy sources Energy source Cost per kwh produced Environmental impact Cons Pros Cons Pros Solar energy High costs involved in manufacturing Cost of fuel (i.e. sunlight) is free Clean energy Large areas must be cleared to make space for the solar panels Wind energy Falling costs due to technological improvements Cost of fuel (i.e. wind) is free Clean energy Spinning turbines cause noise pollution Hydroelectric generation High costs involved in constructing the dam and power plant together maintanence in clearing of slit blocking water flow behind the dam N.A. Clean energy Dams built may disrupt ecosystems 66 Consylladated by Lim Ting Jie

67 (e) state the hazards of using electricity in the following situations: (i) damaged insulation (ii) overheating of cables (iii) damp conditions Hazards of using electricity Damaged insulation Overheating cables Damp conditions If one touches the exposed live wire, electrons flow through the body to Earth May cause severe electric shock, injury and death Many electrical appliances used concurrently Total power drawn from the mains supply may be very large Wires not thick enough will produce high resistance producing more heat Cable becomes overheated to result in a fire Water is a good conductor of electricity Provides conducting path for large current to flow Since the human body has very low resistance Human body is electrocuted when current of more than 50 ma flows through (f) explain the use of fuses and circuit breakers in electrical circuits and of fuse ratings Safety devices Use of fuses Internal wire melts when excessive current flows through The fuse rating on a fuse indicates the maximum current that can flow through it before the fuse starts to melt Protects electrical appliances from damage Ensures safety of the user Must be replaced Use of circuit breakers Switches off electrical supply in a circuit when there is overflow of current The miniature circuit breaker trips when there is a fault in the circuit The Earth leakage circuit breaker switches off all circuits in the house when there is an Earth leakage of more than 25 ma from the live to earth wire May be reset after problem is resolved (g) explain the need for earthing metal cases and for double insulation Safety precautions Need for earthing metal cases In case the live wire comes into contact with the metal casing by accident, someone who touches the casing will be electrocuted To ensure the safety of the user, the metal casing is earthed An earth wire is connected to casing to conduct current away to the earth directly instead of going through the human body Need for double insulation Appliances with plugs of two pins have no earth wire Double insulation insulates electric cable from internal components and insulates the internal components from external casing of these appliances (h) state the meaning of the terms live, neutral and earth Term Live Neutral Earth Meaning Wire which delivers electrical energy to appliance at high voltage, allowing the appliance to function Wire kept at zero volts which forms a current flow path back to the supply to complete the circuit Low resistance wire which connects the metal casing of an equipment to Earth, earthing the appliance continuously to ensure electrical safety of the user in case the metal casing becomes live 67 Consylladated by Lim Ting Jie

68 (i) describe the wiring in a mains plug Wiring in a mains plug Description The cable is made up of 3 wires: the live, netural and earth wires Wire Colour Explanation Live Brown Wired into the pin on the right A fuse is placed between the live terminal and the live pin in the circuit The fuse breaks the circuit if too much current flows Neutral Blue Wired into the pin on the left Earth Green and yellow stripes Wired into the pin on the top (j) explain why switches, fuses, and circuit breakers are wired into the live conductor Wiring of safety devices Switches, fuses and circuit breakers are wired into the live conductor Explanation Switches, fuses and circuit breakers work by breaking an electric circuit By being wired into live conductor, it will be able to prevent current flow from flowing into the conductor at all Damage to the conductor is prevented 68 Consylladated by Lim Ting Jie

69 20. Magnetism syllacon.weebly.com Content Laws of magnetism Magnetic properties of matter Magnetic field Learning Outcomes Candidates should be able to: (a) state the properties of magnets # Aspect Properties of magnets Description of property 1 Magnetic poles Have magnetic poles, where the magnetic effects are strongest 2 Alignment when suspended freely Align themselves to the north and south poles of the Earth when suspended freely 3 Interaction with magnetic materials Attract magnetic materials, which are iron, steel, nickel and cobalt 4 Interaction with other magnets Repel from another magnet with like poles and attracts magnets with unlike poles 5 Identification Can only be identified by repulsion (b) describe induced magnetism Meaning of induced magnetism Magnetic materials are magnetised temporarily when near or in contact with a permanent magnet Mechanism of induced magnetism Magnetic field from the magnetic material aligns with the domains of the permanent magnet (c) describe electrical methods of magnetisation and demagnetisation Electrical magnetisation Magnetic object placed in a solenoid (a cylindrical coil of insulated copper wires carrying currents) Strong magnetic field produced when direct electric current, D.C., flows through the solenoid The magnetic field produced will magnetise the magnetic object Field is determined by right-hand grip rule: Electrical demagnetisation Magnet is inserted into a solenoid and an alternating current, A.C., flows through it When the magnet is withdrawn slowly from the coil, the magnet is constantly being magnetised in opposite directions by the alternating current The domains in the magnet will be arranged different directions, cancelling their magnetic effect Magnetic field around the solenoid causes the magnet to lose its magnetism 69 Consylladated by Lim Ting Jie

70 Properties of magnetised objects Have properties of a magnet Magnetic domains point in the same direction Properties of demagnetised objects Do not have any properties of a magnet Magnetic domains point in random directions No resultant magnetic effect present (d) draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets (e) describe the plotting of magnetic field lines with a compass Examples of magnetic field patterns The magnetic field pattern of a single permanent magnet is shown on the right Field lines travel from N to S outside the magnet Field lines travel from S to N through the magnet Method to draw magnetic field pattern Place the bar magnet at centre of piece of paper so that its North pole faces north and its South pole faces south Place a compass near one pole of the magnet and mark with dots the positions of the North and South ends of the compass needle, labeling them Y and X respectively Move the compass such that the south end of the compass needle is exactly over Y Mark the new posltlon of the north end with a third dot labeled Z Repeat the above until the compass reaches the other pole of the bar magnet Join the series of dots with a curve and this will give a field line of the magnetic field Repeat for more field lines and indicate the direction of the lines (f) distinguish between the properties and uses of temporary magnets (e.g. iron) and permanent magnets (e.g. steel) Differences Temporary magnets Permanent magnets Example Magnetised iron Magnetised steel Nature Soft magnetic material Hard magnetic material Ease of magnetisation Easily magnetised Hard to magnetise Retainment of magnetism Do not easily retain magnetism Easily retains magnetism Uses Electromagnet Transformer core Shielding Magnetic door catch Moving-coil ammeter Moving-coil loudspeaker 70 Consylladated by Lim Ting Jie

71 21. Electromagnetism syllacon.weebly.com Content Magnetic effect of a current Applications of the magnetic effect of a current Force on a current-carrying conductor The d.c. motor Learning Outcomes Candidates should be able to: (a) draw the pattern of the magnetic field due to currents in straight wires and in solenoids and state the effect on the magnetic field of changing the magnitude and/or direction of the current Scenario Patterns of magnetic field due to current Current in solenoids Case Clockwise Anti-clockwise Front-view The arrows represent the direction of current A cross indicates magnetic field lines travelling inwards into the plane (away from you) Representations of arrows and cross/dot can be interchanged (i.e. cross/dot can represent direction of current, arrows represent magnetic field) The arrows represent the direction of current A dot indicates magnetic field lines travelling outwards from the plane (towards from you) Representations of arrows and cross/dot can be interchanged (i.e. cross/dot can represent direction of current, arrows represent magnetic field) Side-view Currents in straight wires Case Current in the same direction Current in opposite directions Magnetic field Illustration Remarks The most common rule used here is the right hand grip rule [which has been illustrated in learning outcome 20(c)] 71 Consylladated by Lim Ting Jie

72 (b) describe the application of the magnetic effect of a current in a circuit breaker syllacon.weebly.com Magnetic effect of current When current is increased to a high level, the solenoid of circuit breaker gains magnetism and becomes a strong electromagnet Stronger magnetic fields produce a force that enables the solenoid to attract iron armature connected in the circuit, breaking the circuit When current is within the limit The solenoid magnetic field is not strong enough to attract the soft iron latch The interrupt point remains closed and current flows normally through the circuit When there is a short circuit or overload A sudden surge of current is present Solenoid gains magnetism and becomes a strong electromagnet due to larger current It is able to attract the soft iron latch and release the spring The safety bar is pushed outward The interrupt point opens and current is cut off 72 Consylladated by Lim Ting Jie

73 (c) describe experiments to show the force on a current-carrying conductor, and on a beam of charged particles, in a magnetic field, including the effect of reversing (i) the current (ii) the direction of the field Current-carrying conductor in magnetic field Current-carrying conductor Magnetic field from magnets Explanation In this case, current that flows outwards in a straight line instead of in a solenoid will cause magnetic field lines to travel anticlockwise Field lines at the top of the wire flow in the same direction as the magnetic field from the magnets On the other hand, field lines at the bottom of the wire flow in the opposite direction as the magnetic field from the magnets Combined diagram Explanation Experimental setup As a result, when the conductor is placed in the magnetic field from the magnets, the magnetic field produced above the wire will be much stronger than the magnetic field produced below the wire The strong resultant magnetic field at the top causes a force to push the conductor downwards Remarks The most common rule used here is Fleming s left-hand rule [which will be illustrated in the next learning outcome] This rule is used only when current from a source causes a force to be produced Beam of charged particles in magnetic field Case Positive charge Negative charge Force direction A cross indicates magnetic field lines travelling inwards into the plane (away from you) Remarks The most common rule used here is Fleming s left-hand rule [which will be illustrated in the next learning outcome] This rule is used only when current from a source causes a force to be produced 73 Consylladated by Lim Ting Jie

74 (d) deduce the relative directions of force, field and current when any two of these quantities are at right angles to each other using Fleming s left-hand rule syllacon.weebly.com Fleming s left-hand rule Function Illustration using current-carrying conductor Legend The relative directions of force, field and currents for both a current-carrying conductor and a beam of charged particles illustrated above can be found using your left hand by Fleming s left-hand rule This rule is used only when current from a source causes a force to be produced F B I Finger Direction Symbol 1 Force F 2 Magnetic field 3 Current I B (e) describe the field patterns between currents in parallel conductors and relate these to the forces which exist between the conductors (excluding the Earth s field) Differences Currents in parallel conductors Case Current in the same direction Current in opposite directions Magnetic field Respective Combined Illustration Explanation The magnetic field lines in between the conductors (both currents travelling inwards) are in opposite directions, cancelling out each other This causes the magnetic field to be stronger in all other areas, pushing the conductors towards each other The magnetic field lines in between the conductors (currents in opposite directions) are in the same direction, which intensifies the magnetic field present there Since the magnetic field is now stronger in between the conductors than all the other areas, the conductors are pushed away from each other 74 Consylladated by Lim Ting Jie

75 (f) explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing (i) the number of turns on the coil (ii) the current Turning effect due to current-carrying coil in a magnetic field Case Due to pivot Due to axis Diagram Explanation As current through the thick, stiff copper wire and magnetic field are perpendicular to each other, by Fleming s left hand rule, a force is produced that pushes the wire away from the powerful permanent magnet Since the bent stiff copper or brass wire acts as a pivot, a perpendicular distance between the pivot and the force is present, thus a clockwise turning effect is also produced As current through the coil and magnetic field are perpendicular to each other at both sides, by Fleming s left hand rule, a force is produced The coil at the side nearer to the N pole is pushed forward as current travels upwards whereas the coil at the side nearer to the S pole is pushed backward as current as travels downwards This produces an anti-clockwise turning effect about a central axis (dotted lines) Increasing force of the turning effect By increasing number of turns of coil Each loop of wires produces its own magnetic field Since the magnetic field strength is the sum of the field lines, more lines will produce a stronger magnetic field and hence greater force By increasing current A larger current will produce a greater concentration of field lines A strong field will lead to a larger force (g) discuss how this turning effect is used in the action of an electric motor Differences Examples Toy cars DVDs Hard disks D.C. motors Uses of electrically produced turning effects Electric fans Hair dryers Washing machines A.C. motors Reason Rotation in a fixed direction is required Alternating rotation in the clockwise and anticlockwise directions is required 75 Consylladated by Lim Ting Jie

76 (h) describe the action of a split-ring commutator in a two-pole, single-coil motor and the effect of winding the coil on to a soft-iron cylinder Split-ring commutator Diagram Description Constant magnetic field by two permanent magnets interacts with the magnetic field in the U-shaped coil due to the direct current Based on Fleming s left hand rule, the wires at each side of the coil experience an equal but opposite force The turning effect created by the two forces causes the coil to rotate continuously in the same direction Split-ring commutator Main components Two permanent magnets D.C. circuit Pair of carbon brushes Split-ring commutator Soft-iron cylindrical core Function of components N and S poles of both magnets face each other Provides the magnetic field (B) Provides the direct current flow (I) Maintains continuous contact between the stationary external D.C. circuit and the split-ring commutator, which is linked to the rotating coil Ensures that the circuit is never broken during rotation Placed between the coil and carbon brushes Reverses direction of current in the coil every half a turn by the coil Ensures the coil rotates in the same (clockwise) direction thoroughout (if it is a continuous ring commutator, the coil will rotate in alternate directions instead) Winding the coil on to a soft-iron cylindrical core concentrates the magnetic field, increasing magnetic field strength 76 Consylladated by Lim Ting Jie

77 22. Electromagnetic Induction syllacon.weebly.com Content Principles of electromagnetic induction The a.c. generator Use of cathode-ray oscilloscope The transformer Learning Outcomes Candidates should be able to: (a) deduce from Faraday s experiments on electromagnetic induction or other appropriate experiments: (i) that a changing magnetic field can induce an e.m.f. in a circuit (ii) that the direction of the induced e.m.f. opposes the change producing it Electromagnetic induction Laws Faraday s law Lenz s law Definition Principles Description of principle E.m.f. generated in a conductor is proportional to the rate of change of the magnetic lines of force linking with the circuit Changing magnetic field can induce an e.m.f. in a circuit Changing magnetic field produces a continuously changing magnetic flux linking with the secondary solenoid Since Faraday s law states e.m.f. generated in a conductor is proportional to the rate of change of the magnetic lines of force linking with the circuit, e.m.f. will be induced, producing a current that will allow power to be transmitted Direction of the induced e.m.f. and hence the induced current in a closed circuit is always such as to oppose the change in the applied magnetic field Direction of the induced e.m.f. opposes the change producing it Since Lenz s law states direction of the induced e.m.f. and hence the induced current in a closed circuit is always such as to oppose the change in the applied magnetic field, the drawing in of a north pole of a magnet into a solenoid (or drawing out of a south pole) will produce a north pole at the end of the solenoid nearest to the magnet as the solenoid will repel the magnet, and vice versa Experiments Opposite direction of magnetic field Opposite direction of magnetic field 77 Consylladated by Lim Ting Jie

78 (iii) the factors affecting the magnitude of the induced e.m.f. Factors to increase the magnitude of induced e.m.f. Increased number of turns of coil Increased strength of magnet Increased speed of movement of magnet or coil Addition of a soft iron core Increased number of turns of coil since more magnetic lines of force produce stronger magnetic field and hence greater force Increased strength of magnet will produce a stronger magnetic field and hence greater force Increased speed of movement of magnet or coil in displacement to each other will increase rate of change of magnetic field lines and frequency of the emf against time graph Addition of a soft iron core since it becomes a magnet within the field lines such that it increases the concentration of magnetic field lines The above factors increase the rate of change of magnetic flux linking the circuit and hence emf by Faraday s law 78 Consylladated by Lim Ting Jie

79 (b) describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings (where needed) (c) sketch a graph of voltage output against time for a simple a.c. generator A.C. generator [read Remarks to understand Fleming s right hand rule first] Diagram of generator Diagram of electrical load Graph of induced e.m.f. / time A.C. voltage from the generator may be received by an electrical load (e.g. light bulb) connected to it induced e.m.f. / mv Use of slip rings Keeps the electrical load in a fixed position (instead of rotating continuously) Maintains continuous contact with the carbon brushes when the coil is rotating This ensures that the alternating current induced in the coil is transferred to the external circuit Description of action of A.C. generator Electromagnetic device which transforms mechanical energy into electrical energy Coil is rotated (usually with a handle) about an axis between the two opposing poles of a permanent magnet When rectangular coil is parallel to the magnetic lines of force, both sides of the coil cuts through the magnetic field lines at the greatest rate, hence induced e.m.f. is maximum The next time rectangular coil becomes parallel to the magnetic lines of force, current will be reversed and thus induced e.m.f. will be minimum When rectangular coil is perpendicular to the magnetic lines of force, it is not cutting through the magnetic field lines The rate of change of magnetic lines of force at this instance is zero, hence no e.m.f. is induced Remarks The most common rule used here is Fleming s right-hand rule, which is used when the application of a force causes current to be produced This is as opposed to Fleming s left-hand rule, which is used only when current from a source causes a force to be produced B F I Factors affecting graph of induced e.m.f. against time Number of coils Strength of magnet Speed of rotation When number of coils doubles, amplitude doubles, frequency doubles and wavelength halves When strength of magnet doubles, only amplitude doubles When speed of rotation doubles, only amplitude doubles 79 Consylladated by Lim Ting Jie

80 (d) describe the use of a cathode-ray oscilloscope (c.r.o.) to display waveforms and to measure potential differences and short intervals of time (detailed circuits, structure and operation of the c.r.o. are not required) Cathode-ray oscilloscope Diagram for understanding only Mechanism for understanding only The electron gun emits a cathode-ray (i.e. beam of electrons) through thermonic emission The electron beam then strikes the flourescent screen, forming a bright spot The deflection system of X and Y plates controls the position the electrons strike on the fluorescent screen It does so by varying the voltage across the X and/or Y plates Uses Measure potential differences Display waveforms of potential differences Measure short time intervals Component required to function Voltage to be measured is applied to the Y-plates via the Y-input terminals The voltage measured is displayed on the fluorescent screen Time-base is switched off to show a fixed voltage or the amplitude of varying voltage Time-base is switched on to check for varying voltage or its frequency and wavelength The device used to measure short time intervals between occurrences (e.g. microphone, when a sound is received at intervals) transmits the information received into voltage The voltage display shown represents the short time intervals to be measured 80 Consylladated by Lim Ting Jie

81 (e) interpret c.r.o. displays of waveforms, potential differences and time intervals to solve related problems Time base / Hz Signals being measured will have a wide range of frequencies Adjusting the time base of input allows us to view the signals to a appropriate range on the screen Y-gain / V The gain determines sensitivity of oscilloscope Adjusted to measure the voltage Examples Example 1 Example 2 Example 3 Example 4 Input 2 V -4 V 20 V -20 V Y-gain 1 V/div 2 V/div 5 V/div 5 V/div Gain-input relationship Line is produced 2/1 = 2 div above Line is produced -4/2 = 2 div below Normal sine curve 20/5 = 4 div Inverted sine curve 20/5 = 4 div A.C. Input Not A.C. (i.e. 0 Hz) Not A.C. (i.e. 0 Hz) 50 Hz 25 Hz Time base 25 Hz 25 Hz 25 Hz 25 Hz Cycles 0/25 = 0 Cycles 0/25 = 0 Cycles 50/25 = 2 Cycles 50/25 = 1 Cycle Graph Graph when time base is turned off 81 Consylladated by Lim Ting Jie