PRE-LEAVING CERTIFICATE EXAMINATION, 2008 MARKING SCHEME PHYSICS HIGHER AND ORDINARY LEVEL

Transcription

1 *WMS13* PRE-LEAVING CERTIFICATE EXAMINATION, 2008 MARKING SCHEME PHYSICS HIGHER AND ORDINARY LEVEL Page 1 of 19

2 In considering this marking scheme the following points should be noted: 1. In many instances only key words are given, words that must appear in the correct context in the candidate s answer in order to merit the assigned marks. 2. Words, expressions or statements separated by a solidus, /, are alternatives which are equally acceptable. 3. Answers that are separated by a double solidus, //, are answers which are mutually exclusive. A partial answer from one side of the // may not be taken in conjunction with a partial answer from the other side. 4. The descriptions, methods and definitions in the scheme are not exhaustive and alternative valid answers are acceptable. 5. The detail required in any answer is determined by the context and manner in which the question is asked and by the number of marks assigned to the answer in the examination paper. Therefore, in any instance, it may vary from year to year. 6. For lack of units, or incorrect units, one mark is deducted, as indicated. 7. Each time an arithmetical slip occurs in a calculation one mark is deducted. Page 2 of 19

3 HIGHER LEVEL Question 1 In an experiment to verify that acceleration is proportional to force applied to a body the following results were obtained. F / N a / m s Draw a suitable graph and explain how these results verify that acceleration is proportional to force. Axes labelled (3) 6 points plotted (3) straight line drawn (3) Straight line through the origin verifies F proportional to a (3) Calculate the mass of the body being accelerated. Find slope of line of best fit m = 3.2 kg (3) Explain clearly how: (i) the acceleration was measured number of dots on tape gives time (3) measure distance, velocity = distance / time (3) repeat for second velocity (3) acceleration = change in velocity / time taken (3) (ii) the force was varied and measured move masses between trolley and pan (3) mass is known (stamped on mass) or measured (3) force = mass 9.8 (3) (iii) the effects of friction were minimised tilt track slightly / dust track, etc. (4) Question 2 A student investigated the variation of the fundamental frequency of a stretched string with tension, T. Draw a labelled diagram of the apparatus used in this experiment. Diagram to show: sonometer, string tension method (3) Tuning fork (3) Spring balance (3) Explain how the tension was varied and measured. Tighten / loosen screw / add weights to pan (3) Read newtonmeter / note weight in newtons (3) The following results were obtained f / Hz T / N T N ½ State the relationship between fundamental frequency and tension. f proportional to T (3) Draw a suitable graph and explain how it verifies the relationship. Values for T (3) Label axes (3) Points plotted straight line drawn (3) Statement: straight line through the origin verifies f α T (3) The student recorded the frequency of the string by noting the frequency stamped on the tuning fork. What justification had he for doing this? Resonance occurs (4) Frequency of string equals (3) Frequency of tuning fork (3) Page 3 of 19

4 Question 3 Calculate a value for the specific latent heat of fusion of ice. The specific heat capacity of water is 4180 J kg 1 K 1 and the specific heat capacity of copper is 390 J kg 1 K 1 (mass of water = 96.3 g mass of ice = 16.1 g Δθ melted ice = 17.6 o C Δθ (Water + ice) = 15.6 o C) ml + mc Δθ(melted ice) = mc Δθ (water) + mc Δθ (calorimeter) (6) L = (6) L = L = 5412 (3) L = L = J kg -1 (3) State two reasons why the ice was crushed before adding it to the warm water. To melt quickly (3) To ensure all ice is at 0 o C (3) Explain why it is beneficial to have the initial temperature of the water a few degrees above room temperature and the final temperature of the water a few degrees below room temperature. Heat lost to room (at start) (3) Equals heat gained from room (at end) (3) Some students in the class used cold water instead of warmed water. They noted that there were tiny drops of water on the outside of the calorimeter at the end of the experiment. (i) where did this water come from? Condensation (from the air) (4) (ii) how did it affect the result of the experiment? extra heat given to the calorimeter (3) incorrect higher final temperature (3) Question 4 Draw a labelled diagram of the apparatus used. Labelled diagram to show Beaker + glycerol (etc) + wire coil (3) Ohmmeter and thermometer (3) Method of heating (3) The following results were recorded Temperature / o C Resistance / Ohms Draw a suitable graph to show how resistance varies with temperature. Graph Labelled axes (3) Points plotted (3) Straight line (3) Explain clearly how the student measured the temperature of the metallic conductor accurately. Remove heat, wait a few minutes Resistance (3) Temperature on thermometer (3) same as temperature of wire (3) The student repeated the experiment to find how the resistance of a thermistor varied with temperature. Sketch the graph that should be obtained Axes drawn and labelled (3) Correct curve Temperature (3) Explain why the resistance of a metal increases with temperature but the resistance of a thermistor decreases with temperature. Metal, when hotter, atoms vibrate more (2) Harder for electrons to pass (2) thermistor, when hotter, more free electrons, reduced resistance (3) Page 4 of 19

5 Question 5 (Eight best answers) (a) State what is meant by a geostationary orbit. Satellite orbits every 24 hours (4) Appears stationary over the earth (3) (b) Tidal power and wave power. Tidal is from the moon Wave from (wind from) the sun (4 + 3) (c) When a gun fires a bullet the kinetic energy gained by the bullet is much greater than that gained by the gun. Explain why. Mass of bullet is much less than gun Velocity of bullet is much greater (due to conservation of momentum) (4) Kinetic energy of bullet is much greater (depends on V 2 ) (3) (d) Explain why a dog whistle can be heard by a dog but not by humans. Whistle is very high frequency (4) Above frequency limits of audibility (3) (e) The diagram shows a convex lens with an object placed between the focal point and the lens. Two rays correctly drawn (4) Image indicated (3) (f) The force on an electron when it is 3 cm from a charge Q is N Find the force on the electron when it is 6 cm from the same charge Q. Distance is doubled so force is one quarter (4) = ¼ of = N (3) (g) Distinguish between intrinsic conduction and extrinsic conduction. Intrinsic: In pure semiconductor due to electrons and holes Extrinsic: Due to impurities / doping (4 + 3) (h) State what is meant by self induction. Induced current in a coil (4) Due to changing current in the coil itself (3) (i) Both the greenhouse effect and the hole in the ozone layer are causing problems. Greenhouse: Causing the earth to heat up Hole in Ozone: Allows (harmful) U.V to pass (4 + 3) (j) State the four fundamental forces of nature. Strong nuclear, weak nuclear, electromagnetic, gravitational ( ) or Draw a truth table for a not circuit (7) Input 1 Output Question 6 Distinguish between a vector and a scalar. Vector has magnitude and direction (3) Scalar has only magnitude (3) Explain why a particle moving in a circle at constant speed experiences acceleration. Direction is changing, hence velocity is changing (3) Hence there is acceleration (3) Describe an experiment to find the resultant of two vectors. 3 spring balances (pulling from one point) (3) Adjust and allow to settle (3) Mark positions and length onto paper (3) Diagonal of parallelogram of any two equal and opposite to third (3) Page 5 of 19

6 Resolve the force of 340 N into its vertical and horizontal components and hence find: Vertical = 340 cos 30 = N Horizontal = 340 sin 30 = 170 N (3) (i) the weight and the mass of the child (ignore the mass of the rope and the seat supporting the child) Weight of child = N (3) Mass of child = / 9.8 = 30 kg (3) (ii) the centripetal force on the child Centripetal force = 170 N (3) It is observed that the ride make one revolution every 6 seconds. Find the radius of the circle the child travels in and state the velocity of the child. (a) ω = 2 π / Τ ω = 2 π / 6 = (3) (b) F = mrω 2 (3) 170 = 30 r (1.047) = r r = 5.16 m (3) Velocity of the child v = ωr = = 5.4 m s -1 (3) A child of 40 kg is also on the ride. Explain angle is still 30 o with the vertical. Centripetal force is greater (3) Weight is greater (proportionally) (3) Angle remains constant (2) Question 7 Both sound waves and light waves undergo interference. Explain what is meant by interference. When two waves meet a new wave is produced (3) Displacement is algebraic sum of displacements (3) State the type of wave that is formed between A and B and explain how this wave is formed. Standing (stationary) wave is produced (3) Two waves travelling in opposite directions meet (3) Interference occurs producing (3) Nodes and antinodes (3) If the distance between adjacent loud spots is 20 cm calculate the speed of sound in air. Distance between antinodes = 20 cm λ = 0.4 m (3) c = f λ = = 328 m s -1 (3) XZ = 36.5 cm and GZ = 80 cm (i) Calculate the angle that the second fringe is formed at tan θ = 36.5 / 80 (3) θ = o (3) (ii) Derive the formula nλ = d sinθ Diagram of triangle with sides nλ and d (3) Sin θ = n λ / d (3) n λ = d Sin θ (3) (iii) Calculate the wavelength of the light d = 1 / (3) 2λ = 1 / sin (3) λ = m (3) When white light passes through the diffraction grating it is dispersed into the spectrum colours. Explain how this dispersion occurs. Different colours Different wavelengths (4) Different angles (4) Page 6 of 19

7 Question 8 Define capacitance. Charge / Voltage (6) The capacitance of a parallel plate capacitor depends on three factors. Area is one, name the other two Distance between the plates (3) Permittivity (3) Describe an experiment to show that the capacitance of a parallel plate capacitor depends on the common area between the plates. Parallel plates, one charged, connected to electroscope (3) Increase (decrease) common area between plates (3) Gold leaves move closer (further) (3) Capacitance has increased (decreased) (3) A parallel plate capacitor has A = m 2 d = 0.4 cm ε = F m -1 Find its capacitance. C = εa / d (3) = / (3) = F (3) The circuit shows a 12 V battery and a resistor of 47 kω and a capacitor of 36 μf Initially there is no charge on the capacitor. (i) Find the current through the resistor the moment the switch is turned on. I = V / R = 12 / = ma (6) (ii) Explain why the current through the resistor becomes less and less and eventually reaches zero. As capacitor charges Voltage across capacitor increases (3) Voltage across resistor decreases Less current through resistor Capacitor is fully charged, no current flows (3) (iii) Find the energy stored in the capacitor when it is fully charged. E = ½ CV 2 = ½ = J (6) State two uses of capacitors. Tuning radio Flash guns Smoothing Filtering (3 + 2) Question 9 Define (i) voltage, work / charge (6) (ii) power work / time (6) From the two definitions deduce the formula P = VI Voltage = work / charge W = VQ Substitute in to power P = W / t = VQ / t P = VI (6) Explain why electrical power is transmitted at high voltages. High voltage (3) Low current (3) Less heat loss because heat produced is proportional to I 2 (3) Sketch a graph to demonstrate what is meant by alternating current, Labelled axes (3) Sine curve (3) Page 7 of 19

8 and state an advantage of using alternating current in the transmission of electric power. can be transformed to different voltages (3) A domestic hot water tank is made of copper. It consists of 35 kg of copper and holds 90 kg of water. Its electric heating element has a resistance of 21 Ω and operates at 230 V. Find how long it takes to heat the water from 13 o C to 60 o C. Heat needed = mc Δθ (copper) + mc Δθ (water) = (3) = = J (3) V = IR 230 = I 21 I = 230 / 21 = A (3) Heat = VIt t = (3) t = 7280 s = 2 hours 80 s. (3) Explain why wires coloured yellow and green may be seen connected to the copper pipes leading to the hot water tank. Bonding Metal fixtures are earthed. All metal pipes, metal taps, metal water tanks, etc. in in a house must be connected to earth (bonded to earth). Bonding to earth is a safety precaution. (3 + 2) Question 10 a Name the antiparticle of the electron and name the scientist who predicted antimatter mathematically. Positron (3) (Paul) Dirac (3) State one similarity and one difference between the electron and its antiparticle. Same mass (3) Opposite charge (3) Name the process whereby the electron and its antiparticle are created from energy. Pair production (3) Write an equation to illustrate this process and explain how charge and momentum are conserved. γ e + + e - OR hf e + + e - (6) (Charge conserved because) Photon has no charge (3) Positron is positive; electron is negative (3) (Momentum conserved) Particles travel in opposite direction (3) Calculate the minimum energy needed to create an electron and its antiparticle, E = mc 2 (3) = 2 ( )( ) 2 (3) = J (3) and hence calculate the minimum frequency of the photon necessary for this process. E = hf (3) (f = E / h) = / ` (3) = Hz (3) Distinguish between leptons, mesons and baryons. Lepton:Indivisible point objects / not subject to strong force Meson: Mass between that of electron and proton / quark and antiquark Baryon: Mass greater or equal to that of proton / 3 quarks or 3 antiquarks ( ) Page 8 of 19

9 Question 10 b What is an electromagnetic relay? Switch in electric circuit (3) Turned on / off by electromagnet (3) With the aid of a labelled diagram explain how an electromagnetic relay works. Diagram to show: Switch and battery (3) Electromagnet (3) Soft iron armature / pivot (3) contacts (3) State two examples where an electromagnetic relay is used in a car, Starter motor (3) Rear window heater / wipers / fan / etc. (3) and explain the advantage of using electromagnetic relay in these circuits. devices draw large current but switch takes only very small current (3) State the principle on which the moving coil galvanometer works, Force on a current-carrying conductor in a magnetic field (6) and describe an experiment to demonstrate this principle. Aluminium foil strip and magnet (3) Turn on current (3) Aluminium strip moves (3) A moving coil galvanometer has a resistance of 80 Ω and a full scale deflection of 4.5 ma. Calculate the size of the resistor required to convert it to a voltmeter with a full-scale deflection of 12 V. Total 12 V with 4.5 ma flowing R = V / I = 2667 Ω (3) Galvanometer = 80 Ω (3) Necessary resistor = = 2587 Ω (3) Explain the role of electromagnetic induction in damping the oscillation of the pointer in a moving coil galvanometer. Induced currents / Eddy currents flow in aluminium former (3) Oppose oscillation by Lenz s law (2) Question 11 Read the following passage and answer the accompanying questions. (a) What is meant by enriched uranium? Greater percentage / proportion of U-235 (7) (b) Why is enriched uranium necessary for a bomb? To ensure chain reaction / U-238 absorbs neutrons, stops chain reaction (7) (c) What experiment did Rutherford carry out that lead him to the nuclear model of the atom? Bombard gold foil with alpha particles (7) (d) Why should uranium and radium be able to produce immense amounts of energy? Mass is converted into energy / E = mc 2 (7) (e) Why is it easier to bombard nuclei with neutrons than with alpha particles? Alpha are positive so are repelled by positive nucleus Neutrons have no charge (7) (f) How does a chain reaction occur in enriched uranium? Each neutron causing fission releases 2 or more neutrons (7) (g) Why does a chain reaction not occur in natural uranium? U-238 absorbs the neutrons produced (7) (h) In a fission bomb at least two pieces of fissile material are brought together very rapidly. Why is it necessary to use more than one piece of fissile material? Each piece is less than the critical size (mass) Together they are greater than the critical size (mass) (7) Page 9 of 19

10 Question 12 Answer any two of the following parts (a), (b), (c), (d). (a) A pole-vaulter just manages to reach a height of 2.9 m. She then lands on a thick mat placed on the ground. The mat is 0.5 m thick. Considering only her motion in a vertical direction state her velocity and her acceleration when she is at the highest point. Velocity = 0 (3) Acceleration = 9.8 m s 2 (3) Downwards (3) Find (i) her speed when she lands v 2 = u 2 + 2as v 2 = x 9.8 x 2.4 v = m s 1 (6) (ii) the time she takes to fall back to the ground v = u + at = t t = 0.7 s (6) Explain the energy changes that take place between the pole and the athlete from the moment she takes off. Potential energy in bent pole (4) Converted to kinetic energy (3) (acceleration due to gravity = 9.8 m s 2 ) (b) State two other sources of background radiation. Outer space / cosmic rays Man-made radioactive materials Nuclear weapons, etc Write an equation for the decay of Radon. (3 + 3) Rn 84Po + 2He ( ) Calculate the decay constant for Radon, days = = s. (3) λ = ln 2 / T 1/2 (3) = / = per second (3) and hence find the activity of a sample of radon containing atoms of radon. Activity = λn ` (2) = = Bq (2) (c) What is meant by electromagnetic induction. E.m.f. is induced when (3) Magnetic flux through a coil changes (3) Distinguish between Faraday s Law and Lenz s Law. Faradays law size of induced e.m.f (3) Lenz s law direction of induced current (3) Page 10 of 19

11 The ring could be made of aluminium, but not of iron. Explain why. Iron is magnetic (3) Aluminium in non-magnetic (3) What happens to the ring when the magnet moves towards it? The ring moves away (4) Explain how this demonstrates Lenz s Law. Induced current opposes movement of magnet (3) Ring moves away (3) (d) Explain the role of electrons in creating X-rays. They are released by thermionic emission (3) They are accelerated by high voltage (3) (When they strike the target) their kinetic energy is converted into X-rays (3) An X-ray tube operates at volts and the electrons carry a current of A across the tube. Find (i) the speed of an electron when it strikes the target Energy = ev = = J (3) ½ mv 2 = (3) v 2 = / (3) v = m s -1 (3) (ii) the number of photons produced per second if 1 % of the electrons produce X-rays 6.4 μa = / = electrons (4) 1 % = photons (3) Page 11 of 19

12 ORDINARY LEVEL Question 1 The diagram shows the apparatus used to measure g, the acceleration due to gravity. The steel ball drops and its acceleration is determined. How is the steel ball held in place before it falls? Electromagnet // string (6) What happens that allows the ball to fall? Turn off magnet/turn switch // cut/burn string (6) What else happens the moment the ball starts to fall? Timer turns on (6) What happens when the ball hits the trapdoor? Circuit is broken / Timer turns off (6) The distance the ball falls through is measured. Explain how this distance is measured accurately? (Measure) from the bottom of the ball to the trap door (6) (Distance = 0.61 m Time = 0.35 s.) Calculate the acceleration due to gravity (s = ½ at 2 ) 0.61 = ½ g(0.35) 2 (3) g = / (3) g = 9.96 m s 2 (4) (-1 for incorrect units) Question 2 A student wished to determine the specific latent heat of fusion of ice. Draw a labelled diagram of the apparatus. Diagram to show Calorimeter (3) Water (3) Ice (3) Thermometer (3) Why was the ice crushed? So that is would melt quickly (6) How did the student know the ice was at 0 o C? It was melting / use thermometer (6) How was the mass of the ice determined? Mass of calorimeter and water and melted ice after (3) Mass of calorimeter and water before (3) Subtract (3) State two ways of improving the accuracy of the experiment. Any two of Insulation / lid / dry the ice / avoid splashing / more sensitive thermometer, etc. (4+3) Page 12 of 19

13 Question 3 A student carried out an experiment to determine the focal length of a convex lens. The following results were obtained. (u = 30, v = 50) 1/30 + 1/50 = 1/f (3) 3/ /150 = 1/f (3) 8/150 = 1/f f = 150/8 (3) f = cm (3) Draw a labelled diagram of the experiment. Diagram to show Light source / object (3) Lens (3) Screen / pin (3) On your diagram mark in the lengths u and v. u and v correctly positioned and labelled (6) Explain how the position of the image was determined. Move the screen (until) (3) Clearest (3) Image (3) Give one precaution to improve the accuracy of your result. Measure to optic centre of lens / Ensure image is clearest / Repeat and take average Avoid error of parallax when measuring (4) Question 4 A student wished to investigate how the resistance of a thermistor varied with temperature. Draw a labelled diagram of the apparatus used. Diagram to show water bath, etc. (3) Thermistor in test tube, glycerol (3) Ohmmeter (shown or mentioned) (3) Thermometer (3) Name the two pieces of equipment used for taking measurements in this experiment, and state what each measured. Thermometer, Temperature (6) Ohmmeter, resistance (6) Explain why the experiment should be done slowly. To ensure temperature measured equals temperature of thermistor / To ensure thermal equilibrium (6) Draw a graph of resistance against temperature. Labelled axis (3) Correctly plotted points (4) Curved line Resistance (3) / Ohms Temperature / o C Page 13 of 19

14 SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks. Question 5 Answer any eight of the following parts (a), (b), (c), etc. (a) Give an example of a scalar and an example of a vector Any correct answer for each, (4) and indicated which is which (3) (b) Boyle s Law concerns the pressure and volume of a gas. Explain why it is an inverse law. As pressure increases volume decreases (or vice versa) (4) Proportionally (3) (c) Why is the acceleration due to gravity less on the moon than it is on the earth? Mass of moon is less than mass of earth (7) (d) Give an advantage of using optic fibres over copper wires. Energy losses are less / (Optical fibres) are smaller (to carry same number of signals) / Less interference (in optical fibres) (7) (e) A person of mass 54 kg is running at 6 m s -1 Find his momentum = 324 (7) (Units not required) (f) Distinguish between potential energy and kinetic energy. Potential energy due to position Kinetic energy due to motion (4 + 3) (g) What is meant by the frequency limits of audibility? The highest and lowest frequency that the human ear can hear (7) (h) Give a use of capacitors. Camera flash Tune a radio To pass a.c. but block d.c. (or filter certain a.c.) Smooth variations in direct current (7) (i) Name the electrical component. Diode (7) (j) State two properties of the electron Negatively charged / has mass / orbits the nucleus/ smallest charge found in nature (4 + 3) Question 6 Define, (i) velocity Rate of change of displacement (6) (ii) acceleration rate of change of velocity (6) Describe an experiment to measure the velocity of a moving object. Ticker timer: time for dot = 1/50 sec (3) Count number of dots to get time (3) Measure distance between dots (3) Velocity = distance / time (3) Page 14 of 19

15 The car can accelerate from rest to 30 m s -1 in 5 seconds. Draw a velocity-time graph to illustrate this motion. 30 Velocity m s -1 Time / s 5 (9) Calculate the acceleration of the car, and the distance it travelled while accelerating. Acceleration = change in vel / time Distance = 30 / 5 = 6 m s 2 (6) = (u + v) / 2 t = (0 + 30) / 2 5 = 75 m (6) If the mass of the car is 1500 kg find the force needed to make the car accelerate. F = ma = = 9000 N (6) Describe the force on the driver when the car brakes and stops. There is a force backwards on the driver (5) v = u + at, s = ut + ½ at 2 F = ma Question 7 There are three types of heat transfer: conduction, convection and radiation. Explain what is meant by conduction of heat. Movement of heat from molecule to molecule (or atom to atom) Without any overall movement of the substance (6) Describe an experiment to compare the rates of conduction through different solids. Number of different rods (3) Wax and drawing pins at one end (or method to show result) (3) Method of heating other end (3) Result (3) A hot water tank has the heating element at the bottom. Explain why. Convection (3) Heat rises (3) A tank contains 75 kg of water. Find the heat needed to increase its temperature from 10 o C to 55 o C. Heat = mc θ = = J = 14.1 MJ (9) Describe an experiment to show that a black metal can radiates more heat than a shiny silver one. Cans with thermometers (3) Fill with hot water (3) Record temperature (3) Can that is cooler has radiated more heat, etc (3) The value of the solar constant is 1.35 kw m -2 Find the amount of energy that falls on a solar panel of area 3 m 2 in 5 seconds when it is perpendicular to the sun s rays. Heat = = kj (11) Specific heat capacity of water = 4180 J kg -1 K -1 (Q = mc θ) Page 15 of 19

16 Question 8 State (i) two properties of bar magnets Two of: Magnetism is strongest to the ends It will attract certain materials to it If suspended it will point North-South Like poles repel / unlike poles attract, etc (3 + 3) (ii) two uses of magnets Fridge magnets In electric motors In loudspeakers (3 + 3) When suspended horizontally a bar magnet will point in a North-South direction. What does this tell us about the earth? The earth has a magnetic field (3) Draw a sketch of a magnetic field due to an electric current in a long straight wire. Sketch to show straight wire (3) Some indication of electric current (3) Circles to show magnetic field (3) State two uses of electromagnets. For lifting scrap iron and steel In electric motors In electromagnetic relay (3 + 3) Describe an experiment to show that a current-carrying conductor in a magnetic field experiences a force. Experiment to show Tin foil strip (3) Magnet (3) Turn on current (3) Tin foil moves (3) State two factors that affect the strength of the force. Two of Length of wire / size of current / strength of magnet (3 + 3) Find the force on a conductor of length 15 cm carrying a current of 2.5 Amps in a magnetic field of 4 Tesla. F = IlB = = 1.5 Newtons (8) Question 9 State what is meant by an electric current. Flow of charge / (or) Charge divided by time (6) Define resistance. Resistance = voltage / current (6) The circuit diagram shows a 12 V battery, a resistor of 50 Ohms and a resistor of 250 Ohms. Calculate (i) the total resistance of the circuit. Resistance = = 300 Ohms (3) (ii) the current flowing in the circuit I = V / R = 12 / 300 = 0.04 Amps (6) (iii) the potential difference across the 50 Ohm resistor V = IR = = 2 Volts (6) Describe an experiment to show the heating effect of an electric current. Container of water with heating coil (3) Method of measuring temperature (3) Temperature increases (3) Page 16 of 19

17 The fuse is a safety device that uses the heating effect of an electric current. Explain how a fuse works and why it is a safety device. When very large current flows (3) Fuse melts/blows (3) No current can flow / stops current (3) Name a device commonly used instead of a fuse, Circuit breaker/ MCB / RCD (3) and give an advantage of it over a fuse. Faster/ more sensitive, etc (3) Give two safety features of the normal 3-pin plug. Has earth connection Has fuse Earth connects first, etc (3 + 2) Question 10 Rutherford carried out a famous experiment. He bombarded a thin sheet of gold foil with alpha particles. Draw a diagram of his experiment. (Any suitable diagram) e.g. alpha particle source, gold foil, detector, or diagram of atoms, and path of alpha particles indicated (6) State what was the result of his experiment. Most alpha particles went straight through (3) Some were deflected / bounced back (3) What did he conclude about the atom? Atoms have positive/dense nucleus (6) Both alpha particles and beta particles are emitted by radioactive substances, but they are different in nature. Explain the difference between alpha and beta particles, Alpha have two protons and two neutrons (3) Beta are (like) electrons (3) and give one example of how they behave differently. Comparison of Deflection in magnetic field/ electric field / ionising power / penetration, etc (6) Name a detector of radioactive particles and outline the principle on which it works. Geiger-Mueller tube (6) Ionisation (3) A radioactive sample has a half-life of 20 minutes. What fraction of the sample remains after one hour? Three half lives (3) One eighth (3) State a precaution that should be taken when dealing with radioactive sources. Minimise time spent Protective clothing Keep sources shielded Use tongs for handling Keep far away from sources Do not eat, smoke, drink (3) Name one harmful effect of radiation. Skin burns Cataracts, leukaemia and other cancers Genetic effects in children (3) Give two uses of radioactive isotopes. Medical imagine Medical therapy Food irradiation Agriculture Radiocarbon dating Smoke detectors Industrial applications (3 + 2) Page 17 of 19

18 Question 11 Read this passage and answer the questions below. (a) What are cathode rays? Beam of electrons (7) (b) Name the process whereby electrons leave a hot cathode. Thermionic emission (7) (c) Give another name for an anode. Positive terminal (7) (d) State a way of deflecting, or focussing, a beam of electrons. Magnetic field / Electric field (7) (e) State the energy changes that occur when cathode rays hit the TV screen. Kinetic energy to Light energy (7) (f) Why are there three colours of dots, red, green and blue on the screen? Primary colours / or explanation (7) (g) Name the process where invisible ultraviolet light is absorbed and then emitted as visible light. Fluorescence (7) (h) Give two advantages of LCD or Plasma screens over the traditional cathode ray tube. The screens are flat / can be viewed from a wider angle. Brighter pictures / higher contrasts / less eyestrain / do not flicker. No annoying scan lines (4 + 3) Question 12 Answer any two of the following parts (a), (b), (c), (d). (a) Define moment of a force. Force by (3) (Perpendicular) distance (3) The diagram shows a spanner 0.40 m long, a force of 180 N is applied. Find the moment of the force = 72 Nm (9) Explain why using a longer spanner, it would be easier to turn the nut. Greater distance, less force needed / Greater distance, greater moment (6) There are upward forces each end of 190 N and 260 N. The weight of the plank is 110 N. Find the weight of the child. Force up = = 450 Weight of child = = 340 N (7) (b) Indicate each. crest trough amplitude wavelength Each item correctly indicated (3 marks each) Both sound and light are wave motions. Give two differences between light waves and sound waves. Light can travel in vacuum Light has much higher frequency Light has much shorter wavelength Light is transverse Light can be polarised And vice versa (Any two, 3 + 3) The speed of light in vacuum is m s -1 A light wave has wavelength m Find the frequency of the wave. F = c / λ = / = ( ) = Hz (6) Page 18 of 19

19 The light wave bends when it passes into glass. What is the name of this process? Refraction (4) (c) Distinguish between an insulator and a conductor. Insulator electricity charge cannot flow through it (3) Conductor electric charge can flow through it (3) Explain, in terms of electrons, how a body can become positively or negatively charged. Positively charged losses electrons OR Negatively charged gains electrons (6) Explain how you would charge the metal spheres by induction. Let spheres touch (3) Bring rod close (3) Separate spheres (3) Give two everyday examples of static electricity Crackling and clinging of clothes Dust attracted to TV screen Sparks can be dangerous in flourmills and oil refineries Aeroplane can build of charge by friction with the air Lightning (Any two: 4 + 3) (d) What is meant by electromagnetic induction? Change in magnetic field (3) passing through a coil / conductor (3) Name one of the scientists whose law describes electromagnetic induction. Faraday / Lenz (3) With the aid of a labelled diagram describe an experiment to demonstrate electromagnetic induction. Coil of wire (3) Galvanometer (or some means of detection) (3) Move magnet into coil (3) Deflection on galvanometer (3) Transformers depend on electromagnetic induction. Give two uses of transformers. (ESB) generating stations / Sub stations Computer / mobile phone charger, etc. Large electric drills/ hammers (4 + 3) Page 19 of 19

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