L.36 PRE-LEAVING CERTIFICATE EXAMINATION, 2014 PHYSICS HIGHER LEVEL TIME 3 HOURS Answer three questions from Section A and five questions from Section B. N.B. Relevant data are listed in the Formulae and Tables booklet, which is available from the Superintendent. 2014 L.36 1/12 page 1 of 12
Answer three questions from this section. Each question carries 40 marks. SECTION A (120 marks) 1. A student measured the distance (d) from the point of suspension of a pendulum to the top of the pendulum bob and measured the time taken (t) for 50 oscillations of the pendulum. She repeated this for a number of different values of d. The diameter of the pendulum bob was measured and found to be 8 mm. The table shows the data recorded by the student. d/cm 39.6 49.6 59.6 69.6 79.6 89.6 99.6 t/s 63.4 70.8 77.6 84.1 89.6 97.1 100.2 Demonstrate the relationship between the period and length of a simple pendulum by using the data in the table to draw a suitable graph. Explain how your graph demonstrates this relationship. (21) The student made an error in one of the readings by miscounting the number of oscillations by one. (i) For which length of pendulum did the student make this mistake? (ii) Did the student count for 49 or 51 oscillations? Justify your answer using the data. (9) Use your graph to calculate a value for g, the acceleration due to gravity. (10) 2014 L.36 2/12 page 2 of 12
2. In an experiment to measure the wavelength of light from a monochromatic source, a narrow beam of the light was incident normally on a diffraction grating with 500 lines per mm. After passing through the diffraction grating, the diffraction pattern produced a number of bright fringes. From the observed pattern, the angle θ between the first order fringe to the left and the first order fringe to the right of the central fringe was measured. This was repeated for the second order and third order fringes. The results for the first and second order fringes are shown below. Angle between first order fringes Angle between second order fringes θ/ 30.4 63.5 Explain how the angular readings presented in the table were calculated from the observed fringes. Use the data in the table to calculate the wavelength of the monochromatic light. (9) Use your result to calculate a value for the angle that could have been measured between the third order fringes. (24) Verify that fourth order fringes could not have been observed. (7) 3. A student performed an experiment to investigate the relationship between the fundamental frequency f of stretched string with its tension T. The length of the stretched string was maintained at 60 cm throughout the experiment. The student collected the following data. f/hz 256 325 354 389 424 480 512 T/N 8.2 13.3 15.9 18.7 22.6 29.4 33.1 Describe how the student obtained the data in the table. (12) Draw a suitable graph to show the relationship between the frequency and the tension of the string. Explain how your graph verifies this relationship. (18) Use the graph to find the mass of the stretched string. (10) 2014 L.36 3/12 page 3 of 12
4. A student performed a series of experiments to investigate the variation of the current I with the potential difference V for a number of components. The graphs drawn from the data recorded for two of the components are shown below. 90 Component A 90 Component B 80 80 70 70 60 60 I (ma) 50 40 I (ma) 50 40 30 30 20 20 10 0 0 1 2 3 4 5 6 7 8 9 V (V) 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 V (V) Identify the components A and B that would have produced the graphs given above. (6) From the graphs identify which of the components, if any, obey Ohm s law. Explain your answer. (8) Explain the variation of current with potential difference for each component as shown in the graphs. (16) Use the graphs to calculate which component has greater resistance at 0.8 V. (10) 2014 L.36 4/12 page 4 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) The volume of a bubble increases three-fold as it rises from the bottom of a lake to the top. What is the depth of the lake? (atmospheric pressure = 1 10 5 Pa; density of water = 1000 kg m 3 ; acceleration due to gravity, g = 9.8 m s 2 ) (b) (c) (d) (e) (f) (g) (h) (i) (j) Define angular velocity. State the thermometric property on which a thermocouple is based. If the sound intensity level at a racetrack increases from 7 db to 19 db when the race begins, by what factor does the sound intensity increase? List two factors that affect the capacitance of a parallel plate capacitor. Distinguish between radial circuits and ring circuits in the home. Sketch the magnetic field due to a current in a solenoid. Why is coolant needed in an X-ray tube? How many alpha-particles and beta-particles are produced 226 214 in the decay reaction 88Ra 83Bi? Write the quark composition of an anti-neutron. or Draw the truth table for an OR gate. (8 7) 2014 L.36 5/12 page 5 of 12
6. (i) Distinguish between scalar quantities and vector quantities and give one example of each. (10) (ii) Describe an experiment that shows how to find the resultant of two vectors. (15) (iii) Why is the acceleration of a ball greater when it slides down a frictionless surface that is inclined at 60 to the horizontal, than when it slides down a frictionless surface that is inclined at 30 to the horizontal? (6) A copper ball of mass 500 g rolls down a surface made of insulating material, inclined at 30 to the horizontal, at constant speed for a distance of 5 m. 30 o (iv) Calculate the force of friction between the ball and the surface. (8) (v) Calculate the amount of heat energy generated due to friction. (9) (vi) Assuming all of the heat energy is absorbed by the ball, calculate the rise in temperature of the ball. (8) (specific heat capacity of copper = 390 J kg 1 K 1 ; acceleration due to gravity, g = 9.8 m s 2 ) 7. (a) Define (i) specific latent heat, (ii) heat capacity. (12) Explain how perspiring helps keep a person cool. Why is it more difficult to cool down on a humid day? (9) In a refrigerator, a heat pump extracts heat from within the fridge. Explain, using a diagram, how this occurs. (15) (b) A sample of ice, of mass 25 g and at a temperature of 8 C was removed from a freezer and added to water at 20 C in a 200 g stainless steel jug. The final temperature of the water settles at 14 C. (i) (ii) Calculate the heat gained by the ice. If 30% of the heat is lost to the surroundings, what mass of water was originally in the jug? (20) (specific heat capacity of ice = 2100 J kg 1 K 1 ; specific heat capacity of water =4180 J kg 1 K 1 ; specific latent heat of fusion of ice = 3.3 10 5 J kg 1 ; specific heat capacity of stainless steel = 510 J kg 1 K 1 ) 2014 L.36 6/12 page 6 of 12
8. What is meant by self-induction? Describe an experiment that demonstrates self-induction. (15) Explain the significance of Lenz s law to self-induction. (9) A dimmer switch features an application of an inductor. Explain how an inductor can cause light to dim as a dimmer switch is rotated. (9) A welding machine requires a step-down transformer, to convert 50 A current in the primary to 250 A current in the secondary. The transformer is 90% efficient and 55 V appears in the secondary. (i) (ii) What is the peak value of the a.c. voltage that must be supplied to the primary coil? Why would there be a difference in the voltage produced in the secondary coil if the same value of d.c. voltage was supplied to the primary coil? (iii) If there are 200 turns in the secondary coil, how many turns are in the primary? (23) 9. What is the photoelectric effect? (6) Describe an experiment that demonstrates the photoelectric effect. (9) How does Einstein s photoelectric law explain the photoelectric effect? (12) Metal Work function (ev) Aluminium 4.08 Caesium 2.1 Platinum 6.35 Magnesium 3.67 Zinc 4.3 Range of wavelength of visible light 390 nm to 700 nm Photons of wavelength 250 nm are incident on a plate. The maximum velocity of the electrons emitted from the plate was measured to be 6.7 10 5 m s 1. (i) What is the energy of the photons? (6) (ii) From the values given in the table, identify the metal in the plate. (11) (iii) Why are all electrons not emitted at the maximum velocity? (3) (iv) Which of the metals (if any) in the table would be suitable for use in a photocell as part of a light intensity meter? Explain your answer. (9) 2014 L.36 7/12 page 7 of 12
10. Answer either part (a) or part (b). (a) List the fundamental forces of nature in increasing order of strength. State where each force is most observed in our universe. (21) Referencing two of these forces, explain why nuclei with significantly more than 100 protons are not observed in nature. (6) Write the equation for a nucleus undergoing beta-decay. (9) For each of the particles involved in this reaction, state whether they are leptons, baryons or mesons. (8) Calculate the total kinetic energy of the products after beta-decay. (12) (b) What is the purpose of a rectifier in an electrical circuit? (6) Input voltage V t Output voltage 1 V t Output voltage 2 V t Draw the rectifier circuits that would produce the output voltages 1 and 2 in the diagrams above from the input voltage shown. (18) Name the type of rectifier in both cases. (6) Indicate where you would place a capacitor in one of the circuits and sketch the output voltage that would result from placing the capacitor there. (9) The input voltage was produced using an a.c. generator. State the principle that underlies the operation of an a.c. generator. (8) Give three factors that affect the size of the a.c. voltage produced in a generator. (9) 2014 L.36 8/12 page 8 of 12
11. Read the following passage and answer the accompanying questions. For thousands of years, astronomers wrestled with basic questions about the size and age of the universe. Does the universe go on forever, or does it have an edge somewhere? Has it always existed, or did it come to being sometime in the past? In 1929, Edwin Hubble, an astronomer at Caltech, made a critical discovery that soon led to scientific answers for these questions. Around 1910, larger telescopes were being built that were able to accurately measure the spectra or intensity of light as a function of wavelength, of faint objects. Using these new data, astronomers tried to understand the overabundance of faint nebulous objects they were observing. Between 1912 and 1922, the astronomer Vesto Slipher at the Lowell Observatory in Arizona discovered that the spectra of light from many of these objects were systematically shifted to longer wavelengths, or red shifted. A short time later, other astronomers showed that these nebulous objects were distant galaxies. Edwin Hubble In 1929, Edwin Hubble, working at Carnegie Observatories in Pasadena, California, measured the red shifts of a number of distant galaxies. He also measured their relative distances by measuring the apparent brightness of a class of variable stars called Cepheids in each galaxy. When he plotted red shift against relative distance, he found that the red shift of distant galaxies increased as a linear function of their distance. The only explanation for this observation is that the universe was expanding. (Adapted from http://skyserver.sdss.org The Expanding Universe) (i) (ii) The spectra of what two elements would astronomers have observed from the study of stars? In these line spectra, why is light of particular wavelengths emitted from a star? (iii) How does intensity of light observed vary with distance from the source? (iv) Convex lenses are used in telescopes. In what two positions can an object be placed so that a magnified image is observed using a convex lens? (v) In a convex lens of power 5 m 1, what is the maximum object distance that would produce an upright image? Explain your answer. (vi) What is the name of the effect that caused red shift as observed by Hubble and Slipher? (vii) How can this effect be demonstrated in the laboratory? (viii) A yellow line of frequency 5.1107 10 14 Hz is emitted from a star moving away from the Earth at 1.5 10 6 m s 1. What is the frequency of the light observed by the astronomer detecting this line on Earth? (8 7) 2014 L.36 9/12 page 9 of 12
12. Answer any two of the following parts (a), (b), (c), (d). (a) State the law of conservation of momentum. (6) Explain how the principle of conservation of momentum applies to the firing of a bullet from a gun. (9) A space shuttle of mass 30000 kg travelling at a speed of 10 m s 1 approaching a docking bay needs to readjust its direction to land in the docking bay, as shown in the diagram. The space shuttle can expel gas either out the front, back or perpendicularly at either side. 100 m Space shuttle 8 m Docking station The space shuttle expels 50 kg of gas perpendicularly to one side. With what speed and in what direction should the gas be expelled in order for the space shuttle to dock successfully with the docking station? (The loss in mass of the space shuttle due to the expulsion of gas may be ignored). (13) (b) What is meant by the critical angle of a substance? (6) Explain, using a labelled diagram, the principle on which an optical fibre is based. (9) A fibre optic cable whose core has a refractive index of 1.62 connects Dublin to New York (a distance of 5100 km). How long does it take a light signal to travel from Dublin to New York through this fibre? (7) State two ways in which you could prevent loss of light from the fibre as it travels from Dublin to New York. (6) 2014 L.36 10/12 page 10 of 12
(c) Define resistivity. (6) Two resistors and a 30 cm length of nichrome wire of diameter 1 mm are connected as shown in the diagram. 12 V 2 Ω 1 Ω Nichrome wire Calculate the total resistance of the circuit. (13) Calculate the current flowing through the nichrome wire. (9) (resistivity of nichrome = 1 10 6 m) (d) What is nuclear fission? (6) Nuclear fission reactors are widely used by countries to provide energy. Why are nuclear fusion reactors not widely used? (6) Give two reasons why nuclear fusion reactors would be preferable to nuclear fission reactors. (6) Explain the purpose of the moderator and the control rods in a fission reactor. (10) 2014 L.36 11/12 page 11 of 12
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