PRE-LEAVING CERTIFICATE EXAMINATION, 2016 MARKING SCHEME PHYSICS HIGHER AND ORDINARY LEVEL

Transcription

1 *WMS13* PRE-LEAVING CERTIFICATE EXAMINATION, 2016 MARKING SCHEME PHYSICS HIGHER AND ORDINARY LEVEL 35 Finglas Business Park, Tolka Valley Road, Finglas, Dublin 11 T: , F: , E: W: Page 1 of 30

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 omission of appropriate units, or incorrect units, one mark is deducted, unless otherwise indicated. 7. Each time an arithmetical slip occurs in a calculation one mark is deducted. Page 2 of 30

3 HIGHER LEVEL Question marks In an experiment to investigate the relationship between the acceleration of a body and the force applied to it, a student recorded the following data. F (N) a (ms 2 ) Describe the procedure involved in measuring the acceleration of the body. measure / calculate the initial velocity / speed (3) measure / calculate the velocity / speed again (t seconds later) (3) measure time interval from initial to final velocities / distance between light gates (3) use relevant formula e.g. v = u + at/v 2 = u 2 + 2as (3) Using the data above, plot a graph showing the relationship between the acceleration of the body and the force applied to it. 3 2,5 y = 4,6369x + 0, F 1,5 1 0, ,,1 0,20 0,,3 0,40 0,,5 0,60 0,,7 a label axes correctly on graph paper (2) plot six points correctly ( 1 per each incorrect/omitted point) (2) straight line (2) good distribution (2) correct statement / correct equation / a α F (2) From your graph, find the mass of the body. correct method for slope (6) m = 4.6 kg [range: kg] (3) ( 1 for omission of for incorrect units) After completing this experiment, the student found that the graph did not go through the origin. Suggest a possible reason for this and describe how the apparatus should be adjusted, so that the graph would go through the origin. friction / any valid reason (6) elevate / adjust the track / slope (3) Page 3 of 30

4 Question marks The specific heat capacity of water was found by adding hot copper to water in a copper calorimeter. The following data was recorded. Mass of calorimeter Mass of calorimeter + water Mass of copper + calorimeter + water Initial temperature of water Temperature of hot copper Final temperature of water 55.7 g g g 16.5 C 99.5 C 21.0 C Describe how the copper was heated and how its temperature was measured. The copper was placed in a boiling tube, plugged with cotton wool, and then placed into a beaker of boiling water for 5 minutes. A thermometer was also left in the boiling tube and it recorded the temperature of the copper. Partly correct (6), fully correct (9) Using the data, calculate (i) The energy lost by the hot copper. E = mcδθ = (3.02 x 10 2 )(390)(78.5) = J (4) (ii) The specific heat capacity of water. Heat lost by copper cooling from 99.5 C to 21.0 C = Heat gained by water in calorimeter rising from 16.5 C to final temperature 21.0 C + Heat gained by copper calorimeter rising from 16.5 C to final temperature 21.0 C. m CU c CU Δθ CU = m W c W Δθ W + m CALC Cu Δθ CAL = (0.0455)(c W )(4.5) + (0.0557)(390)(4.5) c w = 4.04 x 10 3 J kg 1 K 1 (4) Give two precautions that were taken to minimise heat loss to the surroundings. The calorimeter was insulated and a lid was placed on it. The copper was transferred quickly once removed from boiling water. (8) Explain why adding a larger mass of copper would improve the accuracy of the experiment. A larger mass of copper would have caused a greater rise in temperature in the water. This is the measurement with the greatest possible percentage error. Increasing its size reduces that possible percentage error. Partly correct (10), fully correct (15) (specific heat of copper = 390 J Kg 1 K 1 ) Page 4 of 30

5 Question marks In an experiment to measure the speed of sound in air, a cylindrical column of air closed at one end and three different tuning forks were used. A tuning fork of frequency f was set vibrating and held over the column of air. The length of the column of air was adjusted until it was vibrating at its first harmonic and its length l was then measured. This procedure was repeated for each tuning fork. Finally, the diameter of the column of air was measured. The following data was recorded. Describe: f(hz) l(cm) Diameter of column of air = 2.05 cm (i) (ii) How the length of the column of air was adjusted; By lowering or raising an open pipe in a container of water. (3) How the frequency of the column of air was measured; When the column of air was resonating with the tuning fork, the frequency of the tuning fork was the same as the frequency of the air column. This frequency was read from the fork. (3) (iii) How the diameter of the column of air was measured. A vernier callipers measured the internal diameter of the open pipe (3) How was it known that the air column was vibrating at its first harmonic? The open pipe was immersed fully in the container of water and then raised, with tuning fork held at top, until the first position of resonance was located. This first position of resonance corresponded to the fundamental mode of vibration, the first harmonic. (9) Using all of the data, calculate the speed of sound in air. λ/4 = (l + 0.3d), λ = 4 (l + 0.3d) (4) Now, v = f λ = 4f (l + 0.3d) (4) Substituting the values of f, l and the diameter of the air column, d, from the above table gives us v 1 = 340 m s 1 ; v 2 = 342 m s 1 ; v 3 = 341 m s 1 (4) Taking an average of these determined values for the speed of sound, yields V ave = 341 m s 1 (4) Give two ways of minimising errors in the experiment Any two suitable answers. (6) Page 5 of 30

6 Question marks The following is part of a student s report of an experiment to measure the resistivity of nichrome wire. The resistance and length of the nichrome wire were found. The diameter of the wire was then measured at several points along its length. The following data was recorded. Resistance of wire = 32.1 Ω Length of wire = 90.1 cm Diameter of wire = 0.19 mm, 0.21 mm, 0.20 mm, 0.21 mm, 0.20 mm Name an instrument for measuring the diameter of the wire and describe how it is used. Digital callipers/micrometer (2) Place the wire between the jaws (2) Tighten the jaws (2) Read the callipers (2) Why was the diameter of the wire measured at several points along its length? To get an average because the material is not of uniform diameter. Partly correct (4), fully correct (7) Using the data, calculate a value for the resistivity of nichrome. Average diameter = mm A = πr 2 = m 2 ρ =RA/L ρ = (32.1)( )/0.901) ρ = Ω m Partly correct (6), fully correct (10) Give two precautions that should be taken when measuring the length of the wire. Ensure no kinks in wire, only measure length whose R value was measured, avoid parallax error, etc. Any two valid (5+5) The experiment was repeated on a warmer day. What effect did this have on the measurements? Electrical resistivity of metals increases with temperature. (5) Page 6 of 30

7 SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks. Question marks (a) (b) (c) (d) Two forces are applied to a body as shown. What is the magnitude of the resultant force acting on the body? R = 5 N (4) θ = tan 1 (3/4) (3) State Newton s third law of motion. Newton's third law states that for every action (force) (4) there is an equal and opposite reaction. (3) State Boyle's Law. Boyle s Law states that the volume of a given mass of a gas is inversely proportional to the pressure at constant temperature. (4+3) What is the Doppler Effect? The change in frequency of a wave (4) for an observer moving relative to its source. (3) (e) A capacitor of capacitance 2200μF is charged to a potential difference of 20 V. What is the energy stored in the capacitor? E = 1/2 CV 2 (4) E = 0.5 (2200 x 10 6 ) (20) 2 = 0.4 J (3) (f) Draw a sketch of the magnetic field due to a long straight current-carrying conductor. Partly correct (4), fully correct (7) (g) (h) (i) (j) What is meant by the polarisation of waves? Polarised light waves are light waves in which the vibrations occur in a single plane. Partly correct (4), fully correct (7) The activity of a radioactive isotope decays to 1/16 th of its original value after 36 years. What is the half-life of the isotope? 1 1/2 1/4 1/8 1/16 = 4 half-lives (4) Answer: 9 years (3) How are electrons produced in an X-ray tube? Heated filament emits electrons by thermionic emission. Partly correct (4), fully correct (7) A kaon consists of a strange quark and an up antiquark. What type of hadron is a kaon? It is a meson. (7) Or Draw the symbol and truth table for the AND gate Partly correct (4), fully correct (7) Page 7 of 30

8 Question marks Define displacement and acceleration. Displacement is distance in a given direction. (3) Acceleration is the rate of change of velocity with respect to time. (3) A body is travelling with a velocity u in a certain direction. It then accelerates uniformly in the same direction for a time t. Show that s = ut + ½ at 2, where s is the displacement of the body and a is the acceleration. v = final velocity u = initial velocity a = acceleration s = displacement (not distance) t = time Average velocity = (u + v)/2 (2) Displacement = average velocity time (2) s = ((u+v) x t)/2 v = u+at (2) s = ((u + u + at) t)/2 s = ((2 u + at) t)/2 (2) s = ut + ½ at 2 (1) A car accelerates uniformly from rest to a speed of 15 ms 1 in a time of 4 s. It then moves at a constant speed for the next 6 s. (i) Draw a graph showing the variation of velocity with time over the 10 seconds of motion. Velocity (ms 1 ) Time (s) 10 Partly correct (4), fully correct (6) (ii) Calculate the total distance travelled by the car. Distance = area under graph (2) (½ 4 x 15) + 6 x 15 (2) m (2) (iii) Calculate the average speed of the car over the whole journey. Average speed = total distance / total time (4) 120 m / 10 s = 12 ms 1 (2) State Newton s universal law of gravitation. F = (G m 1 m 2 )/d 2 // force proportional to product of masses (3) Correct notation // inversely proportional to distance squared (3) Page 8 of 30

9 A satellite is in a circular orbit of a given radius around a planet. Show that the speed of the satellite is proportional to the square root of the mass of the planet and independent of the mass of the satellite. centripetal acceleration (a = v 2 /R) (2) gravitational acceleration (g = G x M planet /R 2 ) (2) v 2 = a R = (G x M planet /R 2 ) x R = G x M planet /R (2) v = (G x M planet /R) (2) One of the moons of Saturn is in an orbit which has the same radius as that of the Earth s moon. Given that the speed of Saturn s moon is 10 times the speed of the Earth s moon, calculate a value for the mass of Saturn. (mass of the Earth = 6.07 x kg) If v moon S = 10 v moon E, then M sat = 10 2 M e (3) M sat = 100M e = 100 x 6.07 x Kg (3) 6.07 x Kg (3) ( 1 for lack of units or incorrect units) Page 9 of 30

10 Question marks Define specific heat capacity, specific latent heat. The amount of heat required to change a unit mass of a substance by one degree in temperature. Partly correct (4), fully correct (6) The heat needed to change the state of a mass of 1 kg of a substance without changing the temperature Partly correct (4), fully correct (6) 1 kg of water at a temperature of 15 C is placed in a freezer. The freezer has a power rating of 250 W and is 75% efficient. (i) Calculate the energy required to convert the water into ice at a temperature of 20 C. Energy required = energy to cool water from 15 to 0 C + energy to freeze water at 0 C + energy to cool ice from 0 to 20 C. = (m.c.δθ) WATER + (m.l f ) + (m.c. Δθ) ICE = (1 x 4200 x 15) + (1 x 3.3 x 10 5 ) + (1 x 2100 x 20) = = J Partly correct (6), fully correct (9) (ii) How much energy is removed every second from the air in the freezer? 250 W => 250 J removed each second. However, if the freezer is only 75% efficient, then it removes 250 x 0.75 = J of energy from inside each second. Partly correct (6), fully correct (9) (iii) How long will it take the water to reach a temperature of 20 C? To remove J at a rate of J per second takes 2320 s (39 mins) Partly correct (6), fully correct (9) Allowing a liquid to evaporate in a closed pipe inside the freezer cools the air in the freezer. The vapour is then pumped through the pipe to the outside of the freezer, where it condenses again. Explain how this process cools the air in the freezer. The liquid evaporating inside the freezer takes the latent heat of vaporization it requires from the air inside the freezer thereby cooling it. When it condenses again in the pipe outside the freezer it dumps the heat (latent heat of vaporization) it gained inside, into the surroundings. It then passes once more through a compressor into the pipe on the inside where the process repeats itself, leading to a gradual removal of heat from inside the freezer. Partly correct (8), fully correct (12) The freezer causes the room temperature to rise. Explain why. The heat removed inside the fridge is deposited in the room causing it to warm. Also, the fridge is not 100% efficient and would generate heat within the coils of the motor, which would also warm the room. Partly correct (3), fully correct (5) ( 1 for lack of units or incorrect units) (specific heat capacity of ice = 2100 J kg 1 K 1 ; specific heat capacity of water = 4200 J kg 1 K 1 ; specific latent heat of fusion of ice = J kg 1 ) Page 10 of 30

11 Question marks Define power. Rate of doing work / using energy // correct equations and symbols explained Partly correct (4), fully correct (6) Define resistivity. Resistance of a piece of material per unit length and unit area // correct equation and symbols explained Partly correct (4), fully correct (6) Describe an experiment that demonstrates the heating effect of an electric current. apparatus (3) circuit (3) way of detecting heat change (3) result (3) The ESB supplies electrical energy at a rate of 2 MW to an industrial park from a local power station whose output voltage is 10 kv. The total length of the cables connecting the industrial park to the power station is 15 km. The cables have a diameter of 10 mm and are made from a material of resistivity Ω m. Calculate: (i) (ii) The total resistance of the cables. A = πr 2 (3) 7.85 x 10 5 R = ρ L/A (3) 9.5 to 9.6 Ω (3) The current flowing in the cables. W = VI (6) 200 A (3) (iii) The rate at which energy is lost in the cables. (P =) I 2 R (6) W / 0.38 MW (3) Suggest a method of reducing the energy lost in the cables. Thicker cables Lower resistivity / resistance Higher V (tension) Any suitable method (5) ( 1 for lack of or incorrect units) Page 11 of 30

12 Question marks State the laws of refraction of light. The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie in one plane. For any two pairs of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. (Snell s Law) Partly correct (4), fully correct (6) Draw a ray diagram showing the formation of a real image by a converging lens. Object 2F F F 2F Partly correct (6), fully correct (8) An erect image, three times the size of the object, is formed when an object is placed 10 cm from a converging lens. Find the position of the image and the focal length of the lens. m = v/u 3 = v/u, v = 3u u = 10 cm, v = 30 cm 1/f = 1/u + 1/v, 1/f = 1/10 + 1/30, f = 30/4 cm Partly correct (6), fully correct (9) The power of an eye when looking at a distant object should be 60 m 1. A person with defective vision has a minimum power of 66 m 1. Determine the focal length of the lens required to correct this vision. P = P1 + P2 (3) 60 = 66 + P2 / P2 = 6 (m 1 ) (3) P = 1/f / f = 1/P / 1/f = ( ) 6 (3) f = ( ) 1/6 m / ( ) 16.7 cm (3) ( 1 for omission of or incorrect unit) What type of lens is used? Name the defect. Diverging / concave (lens) (3) Short sight / short sightedness / myopia (3) A swimmer cannot see properly when they open their eyes underwater. When underwater: (i) Why does the cornea not act as a lens? light not refracted at cornea (state/imply) (3) water and cornea have the same n value (2) (ii) Why do objects appear blurred? Internal lens not powerful enough to focus light on retina / eye is long-sighted / light not brought to a focus (on the retina) (5) (iii) Explain how wearing goggles allows objects to be seen clearly. light refracted on passing from air to cornea (3) cornea (now) acts as a lens (state/imply) (2) Page 12 of 30

13 Question marks (a) State one law of electromagnetic induction. 1. Faraday s Law states that the size of the induced emf is proportional to the rate of change of flux. 2. Lenz s Law states that the direction of the induced emf is always such as to oppose the change producing it. Either law partly correct (4), fully correct (6) Draw a labelled diagram of an induction coil and explain how it works. Diagram partly correct (4), fully correct (6) When current is supplied to the primary coil, a voltage is induced in the secondary coil that is greater than the voltage applied to the primary the ratio of the voltages is the same as the ratio of the number of turns in the two coils. Explanation partly correct (4), fully correct (6) Define magnetic flux, φ. Magnetic flux is defined as the product of magnetic flux density multiplied by area. φ = BA Partly correct (4), fully correct (6) A flat circular coil of radius 1.6 cm and consisting of 80 turns of wire lies in a plane which is perpendicular to a magnetic field of magnetic flux density 0.20 T. Calculate the magnitude of the induced emf when the flux density is steadily reduced to zero in 0.50 s. E = N (Final Flux Initial Flux) / Time Taken (3) Initial Flux = BA = 0.2 x 3.14 x = (3) Final Flux = 0 (1) E = 80 ( )/0.5 = V / 26 mv (3) Explain the principles involved in each of the following. (i) When a small metal cylinder is dropped through one end of the copper tube shown in the figure, it falls freely under gravity. If the small cylinder is first magnetised, it then takes much longer to fall through the tube. We know that when a magnet and coil move relative to each other, an emf is induced. Now if the coil is a conductor the induced emf will drive a current around the coil. This current has a magnetic field associated with it. The direction of this magnetic field will always be such as to oppose the change which caused it. The moving magnet induces an electric current in the copper. This current creates a magnetic field that exerts a force to oppose the motion of the magnet and hence slows it down. Partly correct (8), fully correct (12) (ii) If a transformer had a solid iron core, the core would get hot when the transformer was in use. Transformer cores are laminated to reduce eddy currents. If we didn t use laminations, the iron core would provide a place for the magnetic lines to produce (induce) current, and that current flowing in the core would heat the core fast and waste energy. By laminating the cores, we break up the current paths within that core and limit eddy currents. Partly correct (6), fully correct (10) ( 1 for omission of or incorrect units) Page 13 of 30

14 (b) What is an alpha particle? (6) a helium nucleus, 4 He Partly correct (4), fully correct (6) 2 What is the change in (i) the atomic number, (ii) the mass number, of a nucleus when an alpha particle is emitted? When an alpha particle is emitted from a nucleus, the nucleus loses two protons and two neutrons. This means the atomic mass number decreases by 4 and the atomic number decreases by 2. Fully correct (i) (6) (ii) (6) Outline an experiment to investigate the range of alpha particles in air. Suitable source (4) Detector, Geiger-Müller tube (4) Reference to activity vs distance (4) In 1911 Ernest Rutherford proposed a new model for the structure of the atom. Describe Rutherford s model of the atom and outline the principle of the experiment that led to this model. It consists of a small, dense, positively charged core with negatively charged electrons in orbit around it. α-particles Gold foil Zinc sulfide screen Correct statement of model (5) They accelerated the protons by injecting them into a tube, across which there was a large potential difference. They detected the alpha-particles, by having them collide with a zinc sulphide screen and observed the resulting scintillations with a microscope. Partly correct (3), fully correct (5) Complete the following nuclear reaction and state its historical significance. 14 N +? 17 O + 1 H He (3) 2 The first nuclear reaction observed by Rutherford. (3) The radioactive isotope radium-226 undergoes alpha decay and has a decay constant of 1.35 x s 1. Calculate the number of alpha particles emitted per second by a 2 μg sample of this isotope. 2 μg = 2 x 10-6 g, 2 x 10 6 g / 226g = 8.9 x 10 9 mol N = 8.9 x 10 9 x 6.02 x = 5.3 x dn/dt = ( ) λn = 1.35 x x 5.3 x Bq Partly correct (6), fully correct (10) ( 1 for omission of or incorrect units) (1 mol of radium-226 = 226 g; the Avogadro constant, N A = 6.02 x mol 1.) Page 14 of 30

15 Question marks Read the following passage and answer the accompanying questions. (a) What does the symbol k represent? kilo, x 10 3 Fully correct (7) (b) (c) (d) (e) (f) (g) (h) Define the unit of voltage. Voltage is electric potential energy per unit charge, measured in joules per coulomb. Partly correct (4), fully correct (7) Explain how a photovoltaic panel produces electricity. Converts the energy of light directly into electricity by the photovoltaic effect. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon. Electrons are excited from their state. Once excited an electron can either dissipate the energy as heat or travel through the cell until it reaches an electrode. Partly correct (4), fully correct (7) The average value for the solar constant in Ireland is 1.2 x 10 2 Wm 2. What is meant by the term solar constant? The solar constant is the amount of energy that normally falls on a unit area (1 m 2 ) of the Earth s atmosphere per second. Fully correct (7) Voltages are expressed as root mean square (RMS) voltages. If the RMS voltage of a source is 230 V, what is the peak output voltage? V RMS = V P / 2 (4) V P = 325 V (3) Small scale wind turbines can be used to charge batteries. The AC output has to be converted to a DC voltage. How is this achieved? diode / rectifier Fully correct (7) What is the tip speed (the linear velocity of the end) of a wind turbine blade of radius 30 cm if it completes a revolution every 3 seconds? T = 2πr/v (4) v = 2 (3.14) (0.3)/3 = ms 1 (3) Micro-CHP units are basically engines which generate electricity. State the principle of operation of an electric motor. An electric motor uses electrical energy to produce mechanical energy through the interaction of magnetic fields and current-carrying conductors. It is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force. Partly correct (4), fully correct (7) ( 1 for lack of or incorrect units) Page 15 of 30

16 Question marks (a) Define density and pressure. Density is the mass of an object divided by its volume. Pressure is the force applied perpendicular to the surface of an object per unit area. (2+2) State Archimedes principle. Archimedes principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces. Partly correct (4), fully correct (6) Weather balloons are released regularly into the atmosphere and carry equipment to monitor atmospheric conditions. A weather balloon made from a material of mass 6 kg is inflated by filling it with hydrogen gas. The total volume of the inflated balloon is 15 m 3. Calculate: (i) (ii) The up thrust on the inflated balloon. Up thrust = weight of air displaced (3) 1.25 x 15 = Kg x 9.8 = N (3) The total weight of the inflated balloon. (Assume that the volume of the gas is the same as the volume of the balloon.) (6) Weight of balloon = 6 x 9.8 = 58.8 N (2) Weight of Hydrogen = 0.12 x 15 = 1.8 Kg x 9.8 = N (2) W 1 + W 2 = N (2) (iii) What is the maximum load that the balloon can carry? Difference = = N = Kg (6) ( 1 for omission of or incorrect units) (Density of air = 1.25 kg m 3 ; density of hydrogen = 0.12 kg m 3 ; acceleration due to gravity = 9.80 m s 2.) (b) Explain the term resonance and describe a laboratory experiment to demonstrate it. Resonance is the response of a body to vibrations of its own natural frequency Partly correct (3), fully correct (5) Take two identical tuning forks mounted on sound boxes. If one of the mounted tuning forks is set vibrating, placed on the bench close to the second tuning fork for several seconds, and then has it vibrations dampened by squeezing the tines between your fingers, it will be heard that the second tuning fork had started vibrating in response to it. This is resonance. Partly correct (7), fully correct (10) Give two characteristics of a musical note and name the physical property on which each characteristic depends. loudness depends on amplitude of the sound wave. pitch depends on frequency of the sound wave. (5 + 4) Explain why a musical tune does not sound the same when played on different instruments. The presence and extent of overtones differ from instrument to instrument. Partly correct (2), fully correct (4) Page 16 of 30

17 (c) Define electric field strength and give its unit of measurement. Electric field strength is the force per unit positive charge at a point in an electric field. Units, Vm 1 or NC 1 Partly correct (6), fully correct (9) The diagram shows a negative charge of 2 μc, positioned 25 cm away from a positive charge of 5 μc. Copy the diagram into your book and show on it the direction of the electric field at point P. Calculate the electric field strength at P. E = 1 / 4πϵ 0 (2 x 10 6 / ) + 1 /4π ϵ 0 (5 x 10 6 / ) (5) E = 1 /4πϵ 0 (2 x 10 6 / x 10 6 / ) (5) E = 3.78 x 10 6 Vm 1 to the left (5) ( 1 for omission of or incorrect units) Under what circumstances will point discharge occur? When charge accumulates at a point to produce a large potential at the point. Valid circumstance (4) (d) In 1939 Lise Meitner discovered that the uranium isotope U 238 undergoes fission when struck by a slow neutron. Barium 139 and Krypton 97 nuclei are emitted along with three neutrons. Write a nuclear reaction to represent the reaction. 238 U n Ba Kr n 0 Partly correct (9), fully correct (12) In a nuclear fission reactor, neutrons are slowed down after being emitted. Why are the neutrons slowed down? How are they slowed down? Why? To increase the chances of capture by U-235 nuclei and cause further fission thus sustaining the reaction. How? By colliding with a moderator such as graphite or heavy water. Partly correct (6), fully correct (9) Fission reactors were once suggested as a partial solution to Ireland s energy needs. Give one positive and one negative environmental impact of fission reactors. positive: Practically no greenhouse gas emission. negative: Radioactive by-products that require long term safe storage. Partly correct (4), fully correct (7) Page 17 of 30

18 ORDINARY LEVEL Question marks In a report of an experiment to verify the principle of conservation of momentum, a student wrote the following: I assembled the apparatus needed for the experiment. During the experiment I recorded the mass of the trolleys and I took measurements to calculate their velocities. I then used this data to verify the principle of conservation of momentum. (i) Draw a labelled diagram of the apparatus used in the experiment. (9) Any suitable diagram, partly correct, two bodies, method of determining velocity etc. (6), fully correct (9) (ii) How did the student measure the mass of the trolleys? (9) By using an electronic balance / weighing scales. Partly correct (6), fully correct (9) (iii) Explain how the student calculated the velocity of the trolleys. (6) Using the light gates to determine the velocity or manually using a ticker tape e.g.: by taking a section of the tape and using the formula velocity = distance/time. They measured the distance between 11 dots and the time was the time for 10 intervals, where each interval was 1 50 th of a second. Partly correct (4), fully correct (6) (iv) How did the student determine the momentum of the trolleys? (12) Using the formula momentum = mass velocity Partly correct (8), fully correct (12) (v) How could the accuracy of the experiment be improved? (4) Any two valid answers, e.g. greater masses give lower percentage errors, higher velocities etc. (2+2) Page 18 of 30

19 Question marks In an experiment to find the speed of sound in air, a student measured the frequency and the wavelength of a sound wave. (i) With the aid of a diagram describe the adjustments they carried out during the experiment. (12) Procedure Set up the apparatus as shown in the diagram. Strike one of the tuning forks on a block of wood and hold it over the resonance tube. Move the inner-tube slowly until the first loud resonant sound is heard. Measure the distance from the top of the resonance tube to the top of the water (l ). This is approximately one quarter of the wavelength. Measure the inner-diameter of the resonance tube (d) using the digital callipers. Note the frequency of the tuning fork; this corresponds to the frequency of the vibrating air column in the resonance tube. The wavelength of sound is calculated using the formula: c = 4f (l + 0.3d) Repeat the procedure with tuning forks of different frequencies. Tabulate the results and get an average value for the speed of sound in air. Diagram partly correct (4), fully correct (6) Procedure partly correct (4), fully correct (6) (ii) How did the student find the frequency of the sound wave? (6) Note the frequency of the tuning fork; this corresponds to the frequency of the vibrating air column in the resonance tube. Partly correct (4), fully correct (6) (iii) How did the student measure the wavelength of the sound wave? (9) Measure the distance from the top of the resonance tube to the top of the water (l ). This is approximately one quarter of the wavelength. Partly correct (6), fully correct (9) (iv) How did the student calculate the speed of sound in air? (9) The speed of sound is calculated using the formula: c = 4f (l + 0.3d) / c = f λ Partly correct (6), fully correct (9) (v) Give one precaution they took to get an accurate result. (4) Ensure that your eye is level with the top of the tube when measuring the length to avoid parallax error / Start with the inner tube fully in the water and slowly raise it so that you don t get a harmonic by mistake / Repeat your efforts to find the loudest resonance position for each tuning fork. Take the average of the attempts. Any valid precaution (4) Page 19 of 30

20 Question marks A student carried out an experiment to measure the wavelength of a monochromatic light source using a diffraction grating. The diffraction grating had 400 lines per mm. (i) Draw a labelled diagram of the apparatus used. (12) Source (4) Diffraction grating (4) Screen (4) (ii) Name a source of monochromatic light. (4) Laser/Sodium Lamp (4) (iii) State what measurements the student took during the experiment. (6) Distance between each line on the diffraction grating, distance of the screen from the grating, spacing of bright spots etc. Partly correct (4), fully correct (6) (iv) What is the distance between each line on the diffraction grating? (6) d = 1/Number of lines per m = 1/ = 2.5 x 10 6 m Partly correct (4), fully correct (6) (v) What difference would occur if the student used a source of white light instead of monochromatic light? (6) Each bright spot would consist of a band of colours which make up white light. (6) (vi) Give one precaution that the student took to get an accurate result. (6) Ensure that the diffraction grating is perpendicular to the (monochromatic) light, use a grating with a large number of lines, ensure D is large, repeat for different orders and take the average, etc. Any valid precaution (6) Page 20 of 30

21 Question marks In an experiment to verify Joule s law, a heating coil was placed in a fixed mass of water. A current I was allowed to flow through the heating coil for a fixed length of time and the rise in temperature Δθ was recorded. This was repeated for different values of the current I. The table shows the data recorded. (i) Draw a labelled diagram of the apparatus used. (12) Ammeter / multimeter, heating coil, thermometer, calorimeter, insulation, stop watch any one (3) any two (2 3) Variable power supply // power supply and variable resistance (3) Detail e.g. closed circuit (3) (ii) How was the current changed during the experiment? (4) Adjust the (variable) power supply // adjust the (variable) resistor (4) (iii) Copy the table and complete it in your answer book. (6) I(A) I 2 (A 2 ) Δθ ( C) Any 3 correct (3), all correct (2 3) (iv) Using the data, draw a graph on graph paper of Δθ against I 2. (12) Label axes correctly, (name / symbol / unit acceptable) (3) Plot three points correctly (3) Plot another three points correctly (3) Straight line (3) If graph paper is not used, maximum mark (3 3) If I 2 is on the Y-axis, maximum mark (3 3) (v) Explain how the graph verifies Joule s law (6) (Straight) line (3) Through origin // shows that Δθ α I 2 (3) Page 21 of 30

22 SECTION B (280 Marks) Five questions to be answered Question 5. any eight parts 56 marks (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) State Newton s second law of motion. The second law states that the acceleration of an object depends on the net force acting upon the object and the mass of the object. Partly correct (4), fully correct (7) Which of the following is not a renewable source of energy? Wind Biofuel Nuclear Hydroelectric Nuclear (7) What is friction? The resistance that one object encounters when moving over another. Partly correct (4), fully correct (7) State Ohm s Law. Ohm s law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Partly correct (4), fully correct (7) How does light travel through an optical fibre? Total internal reflection. (7) Give one use of a capacitor Store electrical energy/ tuning circuits e.g. radios. Partly correct (4), fully correct (7) Name this electrical component A variable resistor. (7) What colour is the neutral wire in an electric cable? Blue. (7) How are X-rays produced? X-rays are produced when electrons strike a metal target. Partly correct (4), fully correct (7) Give two properties of the electron. Negative charge, negligible mass, orbits nucleus, deflected by electric/magnetic field etc. Partly correct (4), fully correct (7) Page 22 of 30

23 Question marks Define the term force and give the unit in which it is measured. (6) That which causes a change in the motion of an object (an object s mass multiplied by its acceleration), newton. Partly correct (4), fully correct (6) Force is a vector quantity. What does this mean? (6) A vector quantity is a quantity that has both magnitude and direction. Partly correct (4), fully correct (6) Give an example of a scalar quantity.(3) A scalar quantity is a one dimensional measurement of a quantity, like temperature, or weight. Fully correct (3) A bumper car of mass 1000 kg was travelling with a speed of 15ms -1 when it struck another stationary bumper car and came to a complete stop in 0.4 s. (i) Draw a diagram of the forces acting on one bumper car before it hit the other. (6) Suitable diagram showing the weight and driving force forwards (can ignore friction) Partly correct (4), fully correct (6) (ii) Calculate the acceleration of the car during the collision. (6) Acceleration = change in velocity / time (2) 0 15 / 0.4 (2) a = 37.5 ms 2 (2) (iii) Calculate the net force acting on the car during the collision. (6) F = ma (2) F = 1000 x 37.5 (2) F = N (2) (iv) Calculate the kinetic energy of the moving bumper car before the collision. (6) KE = ½ mv 2 (2) KE = 0.5 x 1000 x 15 2 (2) KE = J (2) (v) What happened to this kinetic energy? (6) Converted into other forms of energy, sound, heat, some transferred to passengers. Partly correct (4), fully correct (6) (vi) If a regular car was involved in a collision, the driver s momentum (mass velocity) changes from a large value to zero in a short time, possibly causing injuries. What two safety features in cars reduce the possibility of these injuries occurring?(11) Seat belts reduce forward momentum of driver; air bags cushion impact of driver impact to steering wheel etc. Partly correct (7), fully correct (11) Page 23 of 30

24 Question marks Dispersion occurs when a beam of white light passes through a piece of glass, producing a spectrum. (i) What is meant by the terms dispersion and spectrum? (14) Dispersion is the splitting of light into its component colours. A spectrum is the band of colours, as seen in a rainbow, produced by separation of the components of light. Partly correct (4 + 4), both fully correct (7 + 7) (ii) What happens to the white light when it enters the piece of glass?(7) It slows down/changes direction. Partly correct (4), fully correct (7) (iii) Where does dispersion occur in nature? (7) Sunlight passing through raindrops/gem stones Partly correct (4), fully correct (7) (iv) The spectrum of light formed consists of visible and invisible radiation. Give an example of an invisible radiation. (7) Infra Red / Ultra Violet Partly correct (4), fully correct (7) (v) How would you detect an invisible radiation? (7) Feel heat due to Infra-Red; see fluorescence due to Ultra Violet, or any other valid method, ie phone cameras can detect IR flashed from remote controls. Partly correct (4), fully correct (7) (vi) Give one effect of these invisible radiations. (7) Sunburn due to UV exposure / heating due to IR. Partly correct (4), fully correct (7) (vii) What property is common to all of these radiations? (7) Travel at the same speed, undergo diffraction etc. Any valid property (7) Page 24 of 30

25 Question marks (i) Define the term temperature. (6) A temperature is a measure of how hot or cold an object is. Partly correct (4), fully correct (6) (ii) What is the SI unit of temperature? (6) Kelvin, K Partly correct (4), fully correct (6) (iii) The Celsius scale is a common temperature scale. How is the degree Celsius ( o C) related to the SI unit of temperature? (6) One Celsius degree is an interval of 1 K, and zero degrees Celsius if K Partly correct (4), fully correct (6) (iv) Name two methods by which heat can be transferred? (6) Conduction, convection, radiation. Partly correct (4), fully correct (6) (v) Define specific latent heat. (6) The specific latent heat of fusion, l, of a substance is the heat needed to change a mass 1 kg the substance from a solid at its melting point into liquid at the same temperature. Partly correct (4), fully correct (6) 10 g of ice at 0 o C is added to a glass of warm water. All the ice melts quickly and cools the water to 5 o C. Assuming no heat is lost to the surroundings, calculate: (vi) The energy required to melt the ice. (7) E = m ice, l = 0.01 x (4) E = 3300 J (3) (vii) The energy required to warm the melted ice to 5 o C. (7) E = M ice x C ice x Δθ (4) E = 0.01 x 2100 x 5 (2) E = 105 J (1) (viii) Why is it important to stir the mixture? (6) To evenly distribute the heat throughout the mixture. Partly correct (4), fully correct (6) (ix) How could the accuracy of the experiment be improved? (6) Greater mass of ice, resulting in lower percentage error. Insulate container of water so no heat lost/gained from surroundings, etc. Any valid suggestion (6) Specific heat capacity of ice = 2100 J kg 1 K 1 Specific latent heat of fusion of ice = J kg 1 Page 25 of 30

26 Question marks An electric current flows in a conductor when there is a potential difference between its ends. (i) What is an electric current? (6) An electric current is a flow of electric charge / electrons Partly correct (4), fully correct (6) (ii) Give two effects of an electric current. (6) Heating, chemical or magnetic One effect (4), two correct (6) (iii) Name a source of potential difference. (4) Cell/battery, Van De Graaf generators etc. Any valid source correct (4) Describe an experiment to investigate if a substance is a conductor or an insulator. (10) Apparatus: circuit to show power source, ammeter/bulb, leads. (3) Procedure: connect the circuit and place item between contacts. (3) Observation: If the bulb lights then the item is a conductor; if the bulb does not light then the item is an insulator. (4) The two headlights of a truck are connected in parallel to a 24 V supply. (i) Draw a circuit diagram to show how the headlights are connected to the supply. (6) Circuit diagram showing battery and two bulbs connected in parallel. Partly correct (4), fully correct (6) (ii) What is the advantage of connecting them in parallel? (6) If one goes the other still works, they are brighter. Partly correct (4), fully correct (6) (iii) Why should a fuse be included in such a circuit? (6) To prevent too high a current flowing. Partly correct (4), fully correct (6) The resistance of each headlight is 10 Ω. Calculate: (iv) the total resistance in the circuit; (6) For resistors in parallel we use the formula: 1/R = 1/R 1 + 1/R 2 (2) 1/R = 1/10+1/10 = 2/10 = 1/5 (2) R = 5Ω (2) (v) the current flowing in the circuit. (6) V = IR, I = V/R (2) I = 24/5 = 4.8 A (4) (V=IR; 1/R = 1/R 1 + 1/R 2 ) Page 26 of 30

27 Question marks Radioactive elements are unstable and decay with the release of radiation. How would you detect radiation? (6) Use of a Geiger Müller tube, fluorescent screen etc. Any valid detector (6) Name the three types of radiation. (3) Alpha, beta and gamma (1+1+1) (i) Which radiation is negatively charged? (3) Beta particles are negatively charged (3) (ii) Which radiation has the shortest range? (3) The alpha particle is the shortest in range (3) (iii) Which radiation is not affected by electric fields? (3) Gamma radiation is not affected by electric fields (3) Nuclear fission occurs in a nuclear reactor. (iv) What is nuclear fission? (6) A nuclear reaction in which a heavy nucleus splits, with the release of energy. Partly correct (4), fully correct (6) (v) What is the role of neutrons in nuclear fission? (6) In a fission chain reaction, the split atom generates more neutrons as it splits. These neutrons go on to split more atoms in a chain reaction. Partly correct (4), fully correct (6) (vi) Name a fuel used in a nuclear reactor. (6) Plutonium / uranium Any correct source (6) (vii) How can the reaction in a nuclear reactor be controlled? (6) The use of control rods. Fully correct (6) (viii) How is the energy produced in a nuclear reactor used to generate electricity? (9) The energy released is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity. Partly correct (6), fully correct (9) (ix) Give one advantage and one disadvantage of a nuclear reactor as a source of energy. (5) Nuclear power plants don t require a lot of space unlike wind farms, no emissions to atmosphere and does not depend on the weather. Very expensive, decommissioning of nuclear power stations is expensive and takes a long time. Nuclear accidents can spread radiation producing particles over a wide area, This radiation harms the cells of the body which can make humans sick or even cause death. (One correct advantage and disadvantage 3+2) Page 27 of 30

28 Question marks Read this passage and answer the questions below. NASA Confirms Evidence That Liquid Water Flows on Today s Mars (a) What is a spectrometer used for? (7) A spectrometer is an instrument used to view and analyse wavelengths of light. Partly correct (4), fully correct (7) (b) Why was liquid water thought not to exist on Mars? (7) Temperature too low and atmospheric pressure too low/too thin. Partly correct (4), fully correct (7) (c) Why is the discovery of water on Mars important? (7) Water is necessary for life, life could exist on Mars, vital for visiting astronauts. Partly correct (4), fully correct (7) (d) Newton s law of universal gravitation is used to calculate the force between two bodies such as the Sun and Mars. Give two factors which affect the size of the gravitational force between two bodies. (7) Mass of the bodies and the distance between them. One correct (4), Both correct (7) (e) Explain the term acceleration due to gravity, g. (7) The acceleration that an object experiences because of gravity. The value depends on the mass of the planet and the distance between the bodies. Partly correct (4), fully correct (7) (f) Mars is a smaller planet than the Earth. Is the value of gravity, g, greater on the Earth or on Mars? (7) Greater on Earth, due to its larger size. Partly correct (4), fully correct (7) (g) If an astronaut has a mass of 100 kg, what is their weight on Earth? (7) W = mg (4) = 100 x 9.8 = 980 N (3) (h) Would their weight increase, decrease or stay the same on Mars? (7) Weight depends on g, lower g on Mars means lower weight. Partly correct (4), fully correct (7) (Gravity on earth = 9.8 ms 2 ; W = mg) Page 28 of 30

29 Question 12. Answer any two parts 2 28 (a) (i) Define pressure and state the unit it is measured in. (6) Pressure is the force applied to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), equal to one newton per square metre. Definition or unit (4), Both correct (6) Describe an experiment to demonstrate that the atmosphere exerts pressure. (6) Apparatus: glass of water and cardboard (2) Procedure: place cardboard over glass and invert (2) Observation/conclusion: water remains in glass (2) (ii) State Boyle s law. (6) The product of pressure and volume is a constant for a given mass as long as the temperature is constant / PV = constant Partly correct (4), fully correct (6) A balloon rises through the atmosphere while the temperature remains constant. The volume of the balloon is 1 m 3 at ground level where the pressure is 1000 hpa. Find the volume of the balloon when it has risen to a height where the atmospheric pressure is 100 hpa. (6) P 1 V 1 = P 2 V 2 (2) 1 x 1000 = 100 V 2 (2) V 2 = 1000/100 = 10 m 3 (2) What will happen to the balloon as it continues to rise? (4) Volume continues to increase, eventually bursting (4) (b) Define capacitance. (4) The ability of a system to store an electric charge, the ratio of the charge in a system to its electric potential, C = Q/V. Fully correct (4) The figure shows a parallel plate capacitor connected to a battery. Copy the diagram and show the distribution of charges on the plates of the capacitor. (6) Fully correct (6) Give one way in which the capacitance of the capacitor can be changed. (6) Vary the potential difference, area of the plates, spacing between the plates. Any valid method (6) Calculate the charge stored if a 4 μf capacitor is connected to a 6 V battery. (6) Q = CV; (3) Q = 24 μc (3) Give one use of a capacitor. (6) Any valid use (6) Page 29 of 30

30 (c) What is a semiconductor? (7) A solid substance that has a conductivity between that of an insulator and that of a metal. Partly correct (4), fully correct (7) What is the difference between a p-type semiconductor and an n-type semiconductor?(7) One has excess of electrons, the other has excess holes. P-type is doped positively; N-type is doped negatively. Partly correct (4), fully correct (7) The diagram shows a p-n diode being used as a half-wave rectifier. What is the purpose of a half-wave rectifier? (7) Converts an ac voltage to dc voltage Fully correct (7) Sketch a graph to show how the output voltage varies with time. (7) Before use of rectifier After use of rectifier Partly correct (4), fully correct (7) (d) Radon is a radioactive gas which emits alpha particles. Radon gas comes into houses through gaps in the floors. Exposure to radon gas can cause lung cancer. The most stable isotope of radon has a half-life of 4 days. (i) What are isotopes? (6) Different versions of the same element / different numbers of neutrons / different mass numbers. Partly correct (4), fully correct (6) (ii) Why is it important to prevent radon gas entering your home? (6) Exposure to radon gas can cause lung cancer Any valid reason (7) (iii) Define the meaning of the term half-life. (4) The time required for one half the atoms of a given amount of a radioactive substance to disintegrate. Partly correct (4), fully correct (6) (iv) If no more radon gas entered your home, how long would it be until one eighth of the radon gas was left? (6) After 4 days = ½ remains After 8 days = ¼ remains After 12 days = 1/8 remains Partly correct (4), fully correct (6) (v) Give two uses of radioisotopes. (6) Smoke detectors, medicine, production lines of paper, plastic or steel sheeting Any two valid uses (6) Page 30 of 30