*P16* PRE-LEAVING CERTIFICATE EXAMINATION, 2008 PHYSICS HIGHER LEVEL TIME: 3 HOURS Answer three questions from section A and five questions from section B. Page 1 of 12
SECTION A (120 marks) Answer three questions from this section. Each question carries 40 marks. 1. In an experiment to verify that acceleration is proportional to force applied to a body the following results were obtained. F / N 0.98 1.96 2.94 3.92 4.9 a / m s -2 0.31 0.61 0.92 1.23 1.53 Draw a suitable graph and explain how these results verify that acceleration is proportional to force. (12) Calculate the mass of the body being accelerated. (3) Explain clearly how: (i) the acceleration was measured. (12) (ii) the force was varied and measured. (9) (iii) the effects of friction were minimised. (4) 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. (9) Explain how the tension was varied and measured. (6) The following results were obtained. f / Hz 256 288 320 341.3 384 426.6 480 512 T / N 11 14 17 20 25 31 40 45 State the relationship between fundamental frequency and tension. Draw a suitable graph and explain how it verifies the relationship. (15) The student recorded the frequency of the string by noting the frequency stamped on the tuning fork. What justification had he for doing this? (10) Page 2 of 12
3. In order to determine the specific latent heat of fusion of ice some warmed water was put into a calorimeter and some crushed ice was added to it. The following results were recorded. Mass of calorimeter Mass of calorimeter + water Mass of calorimeter + water + melted ice Initial temperature of ice Initial temperature of water + calorimeter Final temperature of water Room temperature = 52.1 g = 148.4 g = 164.5 g = 0 o C = 33.2 o C = 17.6 o C = 22 o C 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 (18) State two reasons why the ice was crushed before adding it to the warm water. (6) 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. (6) 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? (ii) how did it affect the result of the experiment? (10) 4. A student investigated how the resistance of a metallic conductor varied with temperature. Draw a labelled diagram of the apparatus used. (9) The following results were recorded. Temperature / o C 10 23 38 52 68 83 100 Resistance / Ohms 12.2 12.6 13.1 13.5 13.9 14.4 14.9 Draw a suitable graph to show how resistance varies with temperature. (9) Explain clearly how the student measured the temperature of the metallic conductor accurately. (9) The student repeated the experiment to find how the resistance of a thermistor varied with temperature. Sketch the graph that should be obtained. (6) Explain why the resistance of a metal increases with temperature but the resistance of a thermistor decreases with temperature. (7) Page 3 of 12
Answer five questions from this section. Each question carries 56 marks. SECTION B (280 marks) 5. Answer any eight of the following parts (a), (b), (c), etc. (a) State what is meant by a geostationary orbit. (7) (b) (c) Tidal power and wave power are renewable forms of energy, but they are from fundamentally different sources. Explain. (7) When a gun fires a bullet the kinetic energy gained by the bullet is much greater than that gained by the gun. Explain why. (7) (d) Explain why a dog whistle can be heard by a dog but not by humans. (7) f f (e) (f) (g) The diagram shows a convex lens with an object placed between the focal point and the lens. Copy and complete the ray diagram to show the position of the image. (7) The force on an electron when it is 3 cm from a charge Q is 5.2 10-12 N Find the force on the electron when it is 6 cm from the same charge Q. (7) Distinguish between intrinsic conduction and extrinsic conduction in semiconductors. (7) (h) State what is meant by self induction. (7) (i) Both the greenhouse effect and the hole in the ozone layer are causing problems. State the problem that each causes. (7) (j) State the four fundamental forces of nature. (7) or Draw a truth table for a not circuit. (7) Page 4 of 12
6. Distinguish between a vector and a scalar. (6) Explain why a particle moving in a circle at constant speed experiences acceleration. (6) Describe an experiment to find the resultant of two vectors. (12) The diagram represents a ride at a funfair, with one child in a chair on the ride. When stationary the chairs hang vertically. When it is rotating the chairs swing out such that their supporting ropes make an angle of 30 o with the vertical. The total tension in the ropes is 340 N Resolve the force of 340 N into its vertical and horizontal components and hence find. (i) The weight and the mass of the child. (ignore the mass of the rope and the seat supporting the child) (ii) The centripetal force on the child. (12) It is observed that the ride makes one revolution every 6 seconds. Find the radius of the circle the child travels in and state the linear velocity of the child. (12) A child of 40 kg is also on the ride. Explain why the ropes supporting him also make an angle of 30 o with the vertical. (8) (acceleration due to gravity = 9.8 m s -2 ) Page 5 of 12
7. Both sound waves and light waves undergo interference. Explain what is meant by interference. (6) Loudspeaker Laudspeaker Wall A A loudspeaker produces a sound of frequency 820 Hz. The sound is reflected off the wall. As an observer moves from A to B it is noticed that the sound becomes louder and quieter in a regular manner. State the type of wave that is formed between A and B and explain how this wave is formed. (12) If the distance between adjacent loud spots is 20 cm calculate the speed of sound in air. (6) A teacher wished to determine the wavelength of light from a laser. He let light from a laser pass through a diffraction grating, G, of 300 lines per mm. A series of bright fringes, X, Y, and Z were formed on a screen. (The laser also produced a bright spot at Z without the grating) X B Laser Y G Z XZ = 36.5 cm and GZ = 80 cm (i) Calculate the angle that the second fringe is formed at. (6) (ii) Derive the formula nλ = d sinθ (9) (iii) Calculate the wavelength of the light. (9) When white light passes through the diffraction grating it is dispersed into the spectrum colours. Explain how this dispersion occurs. (8) Page 6 of 12
8. Define capacitance. (6) The capacitance of a parallel plate capacitor depends on three factors. Area is one, name the other two. (6) Describe an experiment to show that the capacitance of a parallel plate capacitor depends on the common area between the plates. (12) A parallel plate capacitor has A = 0.0068 m 2 d = 0.4 cm Find its capacitance. (9) 12 V 47 kω 36 μf 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. (6) (ii) Explain why the current through the resistor becomes less and less and eventually reaches zero. (6) (iii) Find the energy stored in the capacitor when it is fully charged. (6) State two uses of capacitors. (5) (permittivity of free space = 8.9 10-12 F m -1 ) Page 7 of 12
9. Define (i) voltage, (ii) power. (12) From the two definitions deduce the formula P = VI (6) Explain why electrical power is transmitted at high voltages. (9) Sketch a graph to demonstrate what is meant by alternating current, and state an advantage of using alternating current in the transmission of electric power. (9) 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 C to 60 C. (15) Explain why wires coloured yellow and green may be seen connected to the copper pipes leading to the hot water tank. (5) (The specific heat of water is 4180 J kg 1 K 1 and the specific heat capacity of copper is 390 J kg 1 K 1.) Page 8 of 12
10. Answer either part (a) or part (b). (a) Name the antiparticle of the electron and name the scientist who predicted antimatter mathematically. (6) State one similarity and one difference between the electron and its antiparticle. (6) Name the process whereby the electron and its antiparticle are created from energy. (3) Write an equation to illustrate this process and explain how charge and momentum are conserved. (15) Calculate the minimum energy needed to create an electron and its antiparticle and hence calculate the minimum frequency of the photon necessary for this process. (18) Particle accelerators create numerous particles, initially described as a particle zoo However, they are now grouped under three headings: leptons, mesons and baryons. Distinguish between leptons, mesons and baryons. (8) (Speed of light = 3 10 8 m s -1 Mass of electron = 9.1 10-31 kg Plank s constant = 6.6 10-34 J s) (b) What is an electromagnetic relay? (6) With the aid of a labelled diagram explain how an electromagnetic relay works. (12) State two examples where an electromagnetic relay is used in a car and explain the advantage of using electromagnetic relay in these circuits. (9) State the principle on which the moving coil galvanometer works and describe an experiment to demonstrate this principle. (15) 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. (9) Explain the role of electromagnetic induction in damping the oscillation of the pointer in a moving coil galvanometer. (5) Page 9 of 12
11. Read the following passage and answer the accompanying questions. On August 2, 1939, Albert Einstein wrote to then President Franklin D. Roosevelt. Einstein and several other scientists told Roosevelt of efforts in Nazi Germany to purify uranium-235, which could be used to build an atomic bomb. The most complicated issue to be addressed in the making of an atomic bomb was the production of ample amounts of enriched uranium to sustain a chain reaction. The first decades of the twentieth century led to changes in the understanding of the physics of the atom. Chief among these developments were the discovery of a nuclear model of the atom. Study on the phenomena of radioactivity began with the discovery of uranium ores by Becquerel and of radium by the Curies Their research seemed to promise that atoms, previously thought to be ultimately stable and indivisible, actually had the potential of containing and releasing immense amounts of energy. But even in the early 1930s such illustrious physicists as Ernest Rutherford and Albert Einstein could see no way of artificially releasing that energy any faster than nature naturally allowed it to leave. In 1934, Irene and Frederic Joliot-Curie discovered that artificial radioactivity could be induced in stable elements by bombarding them with alpha particles. The same year Enrico Fermi reported similar results when bombarding uranium with neutrons (discovered in 1932), but he did not immediately appreciate the consequences of his results. (a) What is meant by enriched uranium? (7) (b) Why is enriched uranium necessary for a bomb? (7) (c) What experiment did Rutherford carry out that lead him to the nuclear model of the atom? (7) (d) Why should uranium and radium be able to produce immense amounts of energy? (7) (e) Why is it easier to bombard nuclei with neutrons than with alpha particles? (7) (f) How does a chain reaction occur in enriched uranium? (7) (g) Why does a chain reaction not occur in natural uranium? (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? (7) Page 10 of 12
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. (9) Find (i) the time she takes to fall back to the mat. (6) (ii) her speed when she lands. (6) Explain the energy changes that take place between the pole and the athlete from the moment she takes off. (7) (acceleration due to gravity = 9.8 m s -2 ) (b) Radon from granite is a source of background radiation. State two other sources of background radiation. (6) Radon (Rn) has a half-life of 3.825 days. It decays by emitting and alpha particle. Write an equation for the decay of Radon. (6) Calculate the decay constant for Radon and hence find the activity of a sample of radon containing 5.6 10 15 atoms of radon. (12) State a health hazard of ionising radiation. (4) (see Mathematical Tables, p.44) Page 11 of 12
(c) What is meant by electromagnetic induction? (6) Distinguish between Faraday s Law and Lenz s Law. (6) String To demonstrate Lenz s law the magnet is moved towards the ring. The ring could be made of aluminium, but not of iron. Explain why. (6) What happens to the ring when the magnet moves towards it? (4) Explain how this demonstrates Lenz s Law. (6) (d) Explain the role of electrons in creating X-rays. (9) An X-ray tube operates at 80, 000 volts and the electrons carry a current of 6.4 10 6 A across the tube. Find (i) the speed of an electron when it strikes the target. (12) (ii) the number of photons produced per second if 1 % of the electrons produce X-rays. (7) (Charge on the electron is 1.6 10 19 C, mass of electron = 9.1 10 31 kg.) Page 12 of 12