PHYSICS HIGHER LEVEL

Transcription

1 PRE-LEAVING CERTIFICATE EXAMINATION, 2009 PHYSICS HIGHER LEVEL Ti m e : 3 h o u r s Answer three questions from section A and five questions from section B. Page 1 of 8

2 SECTION A (120 marks) Answer three questions from this section. Each question carries 40 marks. 1. In order to investigate the relationship between the period and the length of a simple pendulum, a pendulum was attached to a retort stand in such a way that it could swing freely about a fixed point. The length of the pendulum was measured. It was set swinging through a small angle and the time for 30 oscillations, t, was found. This procedure was repeated for a series of values of the length 1. The following results were obtained: 1 / cm t / s Draw a suitable graph to illustrate the relationship between the period and the length of the pendulum. (12) Hence determine a value for the acceleration due to gravity, g. (9) (i) How is the pendulum set up so that it swings freely? (6) (ii) Explain why the pendulum is only allowed to swing through a small angle. (6) (iii) How does the number of oscillations affect the accuracy of the experiment? (7) 2. In an experiment to measure the wavelength of light emitted by a monochromatic source, a narrow beam of the light fell normally on a diffraction grating. The grating had 500 lines per millimeter. A diffraction pattern was produced. The angle between the first order image on the left and the first order image on the right of the central bright image was measured and found to be Describe, with the aid of a labelled diagram, how the data was obtained. (9) Name a source of monochromatic light. (6) Use the data to calculate the wavelength of the monochromatic light. (15) What is the highest order diffracted image formed? (6) Explain how using a diffraction grating of 300 lines per millimeter leads to a less accurate result. (4) Page 2 of 8

3 3. In an experiment to measure the specific heat capacity of a liquid, a quantity of the liquid was heated in a copper calorimeter. The following measurements were obtained: Mass of calorimeter = 26.5g Mass of calorimeter + liquid = 71.3g Initial temperature of calorimeter + liquid = 16 o C Final temperature of calorimeter + liquid = 21 o C Energy supplied = 584 J Using these measurements, calculate a value for the specific heat capacity of the liquid, given that the specific heat capacity of copper is 390 J kg 1 K 1. (15) Describe the apparatus which might have been used in this experiment in addition to the calorimeter. (9) Give three ways in which heat losses from the calorimeter might have been reduced in this experiment. (9) Explain why using a larger mass of the liquid while supplying the same amount of energy might have produced a less accurate result. (7) 4. In an experiment to verify Joules law, a heating coil was placed in a fixed mass of water. The current was allowed to flow for a fixed interval of time. The temperature rise Δθ produced for different values of the current I passed through the coil, was recorded. The table below shows the recorded data: I / A Δθ / o C Describe, with the aid of a labelled diagram, how the apparatus was arranged in this experiment. (12) Draw a suitable graph and explain how your graph verifies Joules law. (18) Explain why a fixed mass of water was used each time. (5) Why do overhead cables use a high voltage rather than a high current? (5) Page 3 of 8

4 SECTION B (280 marks) Answer five questions from this section. Each question carries 56 marks. 5. Answer any eight of the following parts (a), (b), (c), etc. (a) (b) A mass of 5 kg moving at 20 ms 1 collides with a mass of 35 kg which is at rest. After the collision, both masses move on together as a combined mass. Calculate the velocity of the combined mass. (7) Calculate the horizontal component of a force of 25 N acting at 60 o to the horizontal. (7) (c) The resistance of an element in the water of an immersion heater was 60 Ω. The resistance of the same element was 12Ω at 0 o C and 92 Ω at 100 o C. What was the temperature of the water in the immersion heater? (7) (d) (e) The solar constant is 1.35 kwm 2. What is the average amount of energy falling normally on each square metre of the earth s upper atmosphere in one year? (1 year = 3.16 x 10 7 s) (7) An object is placed 30cm from a concave lens and the image is formed 20 cm from the lens. Calculate the focal length of the lens. (7) (f) Explain the difference between db and db(a). (7) (g) What is meant by pair annihilation? (7) (h) What is the magnetic flux through a rectangular area of dimensions 2 m and 80 cm, placed at right angles to a uniform magnetic field of 5T? (7) (i) Define the unit of current, the ampère. (7) (j) State the quark composition of a meson. or (j) An OR gate has two inputs, A and B. In what circumstances will the output of the gate be high? (7) Page 4 of 8

5 6. (a) State the principle of moments. (6) Fig.1 shows a uniform beam supported at its centre. Two bodies A and B, each of weight 20 N, are suspended from the beam so that body B rests on the bottom of a beaker as shown in the diagram. The two bodies are suspended at distances of 40 cm and x, respectively, from the centre of the beam. When water is poured into the beaker the beam gradually turns towards the horizontal. Explain why the beam turns towards the horizontal as water is poured into the beaker. (9) When body B is covered in water, the beam is horizontal and in equilibrium. Given that the volume of B is m 3 calculate the distance x. (18) (Density of water = kg m 3 ; acceleration due to gravity, g = 9. 8 ms 2 ) A 40 cm x Fig.1 B (b) State Newton s law of gravitation. (6) 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. (8) One of the moons of Saturn is in an orbit which has approximately 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. (9) (Mass of Earth = kg) 7. At the beginning of the nineteenth century, an English scientist showed that light undergoes interference and diffraction, using two coherent sources. (a) Name the English scientist. (6) (b) Explain the underlined terms. (18) Light travels as transverse waves while sound travels as longitudinal waves. Explain the difference between longitudinal and transverse waves. (9) Describe an experiment to demonstrate that light is a transverse wave. (9) What is the Doppler effect? (6) A bungee jumper in free-fall screams on the way down with a frequency of 550 Hz. What frequency is heard by people observing on the ground below her, when she travels with a downfall speed of 15 ms 1. (8) (Speed of sound in air = 340 ms 1 ) Page 5 of 8

6 8. A uranium ore was discovered by Marie and Pierre Curie to contain the two radioactive isotopes, radium and polonium. Explain the underlined words. (12) Radium-226 decays to polonium-218 in two stages, with the same particle emitted in each stage. Name this particle and give an equation for the process. (12) Outline an experiment to demonstrate the ionising effect of the particles emitted. (12) Given that the half-life of radium-226 is very much greater than the half-life of polonium-218 explain why you would expect to find much more radium-226 than polonium-218 in a sample of the uranium ore. (6) If a sample of radium contains radium-226 nuclei and is emitting particles per second calculate (i) the decay constant, (ii) the half-life, of radium-226. (14) 9. (a) Define resistivity. (6) Describe an experiment to measure the resistivity of the material of a wire. (13) A 10 Ω resistor consists of a piece of wire of uniform cross-sectional area and of length 65 cm. If the resistivity of the material of the wire is Ω m, what is the diameter of the wire? (11) C (b) State Coulomb s law of force between electric charges. (6) Define the term electric field intensity. (6) Two positive point charges, each of 1. 2 μc are situated at the vertices A and C of a right-angled isosceles triangle as shown. Calculate the total electric field intensity at B given that AB = BC = 40 cm. A B (14) (Permittivity of free space, Єo = Fm 1 ) 10. What is the photoelectric effect? (6) Give an expression for Einstein s photoelectric law. (9) Light of wavelength m falls on a metal which has a work function of 2. 3eV. Calculate the maximum kinetic energy of the emitted electrons. (15) Fig.2 shows a photodiode connected in series with a battery and a galvanometer. Why is it not necessary to have a resistor in series with the photodiode as it would be for a light-emitting diode (LED)? (6) State the relationship between the intensity of the light falling on the photodiode and the current flowing through the galvanometer. Explain how this relationship arises. (6) Light falls on the photodiode at a rate of 0. 24mW. The light is monochromatic light and of wavelength m. Calculate: Fig.2 (i) The energy of one photon of the light. (ii) The number of photons striking the photodiode surface per second. (Speed of light in a vacuum, c = ms 1 ; charge on electron, e = C; Planck s constant, h = Js). (14) Page 6 of 8

7 11. Answer either part (a) or part (b). (a) In a nuclear reaction there are 3 laws of conservation. Name them. (9) In the reaction. Ra Rn + He + energy (b) J of energy are released as the kinetic energies of the products. If the ratio of the masses of 86Rn to 2He is 222:4, find the kinetic energy of the alpha particle. (15) An electron and a positron are examples of anti-matter. Give the charge (both sign and magnitude) of each. (5) Calculate the minimum energy, in MeV, of a gamma ray photon to produce an electron and a positron. (9) Particle accelerators create numerous particles, initially described as the particle zoo. Such particles are now grouped under three headings: leptons, mesons and baryons. Give (i) an example (ii) a property of each of these particles. (18) (Mass of electron = kg, c = ms 1, e = C). or State the principle on which the moving coil galvanometer is based and name one other device which is based on the same principle. (9) Use a circuit diagram to show how a resistor may be used to convert a galvanometer to (a) an ammeter, (b) a voltmeter. Comment on the size of the resistor in each case. (12) A moving coil galvanometer has a resistance of 50 Ω and a full-scale deflection of 5 ma. Calculate the size of the resistor required to convert it into an ammeter with a full-scale deflection of 1 A. What is the effective resistance of the ammeter? (15) A transformer and an induction coil can both be used to change a small voltage into a larger voltage. What is the basic difference in the operation of these two devices? (6) Give 2 factors that affect the efficiency of a transformer. (6) An electrical device bought in America, where the mains electricity is supplied at 110V, is to be used in Ireland, where the mains voltage is 230V. (i) (ii) What type of transformer in needed? If there are 220 turns on the secondary coil of the transformer used, how many primary turns does it have? (8) Page 7 of 8

8 12. Answer any two of the following parts (a), (b), (c), (d). (a) A body starts with an initial velocity u and a constant acceleration a. Derive an expression for its displacement after time t in terms of u and a. (12) A body of mass 2 kg is thrown upwards with an initial velocity u from a point P which is 14 m above the ground. After 2. 8 s it is at a point Q and its velocity is 18 ms 1 downwards. Find the value of u and the height of Q above the ground. (16) (b) State the laws of refraction of light. (6) Describe an experiment to measure the focal length of a converging lens. (12) Explain the significance of conjugate foci. (10) (c) State Lenz s law of electromagnetic induction. (6) Describe an experiment to illustrate this law. (12) The resistance of the lamp in the circuit in Fig.3 is 60 Ω. If the resistance of the rest of the circuit is negligible, calculate the electromotive force (e.m.f.) induced in the coil when the current flowing through the lamp is 80 ma. (10) 12 V Fig.3 L (d) The following is part of a student s account of an experiment to plot the characteristic curve of a diode. In the experiment the diode was forward biased and a resistor was connected in series with it. The measurements were taken and plotted on a graph. The diode was then reverse biased and the measurements repeated. These measurements were also plotted on the graph. Explain what is meant by forward biasing the diode. (6) Draw a circuit diagram for this experiment with the diode in forward bias. (12) Sketch the graph which could have been obtained with the diode in forward bias. (6) Explain why the resistor was connected in series with the diode. (4) Page 8 of 8