9702_s12_qp_42
A paper of Physics, 9702
Questions:
12
Year:
2012
Paper:
4
Variant:
2
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1
State Newton’s law of gravitation. The Earth and the Moon may be considered to be isolated in space with their masses concentrated at their centres. The orbit of the Moon around the Earth is circular with a radius of 3.84 × 105 km. The period of the orbit is 27.3 days. Show that the angular speed of the Moon in its orbit around the Earth is 2.66 × 10–6 rad s–1, the mass of the Earth is 6.0 × 1024 kg. For Examiner’s Use The mass of the Moon is 7.4 × 1022 kg. Using data from , determine the gravitational force between the Earth and the Moon. force = N Tidal action on the Earth’s surface causes the radius of the orbit of the Moon to increase by 4.0 cm each year. Use your answer in to determine the change, in one year, of the gravitational potential energy of the Moon. Explain your working. energy change = J
5. Work, energy and power  →  5.2. Gravitational potential energy and kinetic energy
13. Gravitational fields  →  13.2. Gravitational force between point masses
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2
For Examiner’s Use A ball of mass 37 g is held between two fixed points A and B by two stretched helical springs, as shown in . ball mass 37 g A B The ball oscillates along the line AB with simple harmonic motion of frequency 3.5 Hz and amplitude 2.8 cm. Show that the total energy of the oscillations is 7.0 mJ. At two points in the oscillation of the ball, its kinetic energy is equal to the potential energy stored in the springs. Calculate the magnitude of the displacement at which this occurs. displacement = cm For Examiner’s Use On the axes of and using your answers in and , sketch a graph to show the variation with displacement x of the total energy of the system (label this line T), the kinetic energy of the ball (label this line K), the potential energy stored in the springs (label this line P). –3 –2 –1 energy / mJ x / cm The arrangement in is now rotated through 90° so that the line AB is vertical and the ball oscillates in a vertical plane. Suggest one form of energy, other than those in , that must be taken into consideration when plotting new graphs to show energy changes with displacement.
17. Oscillations  →  17.2. Energy in simple harmonic motion
5. Work, energy and power  →  5.1. Energy conservation
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4
For Examiner’s Use A charged point mass is situated in a vacuum. A proton travels directly towards the mass, as illustrated in . proton r charged point mass When the separation of the mass and the proton is r, the electric potential energy of the system is UP . The variation with r of the potential energy UP is shown in . –40 –50 –30 –20 –10 r / cm UP / 10–26 J For Examiner’s Use Use to state and explain whether the mass is charged positively or negatively. The gradient at a point on the graph of is G. Show that the electric field strength E at this point due to the charged point mass is given by the expression Eq = G where q is the charge at this point. Use the expression in and to determine the electric field strength at a distance of 4.0 cm from the charged point mass. field strength = V m–1
18. Electric fields  →  18.5. Electric potential
18. Electric fields  →  18.4. Electric field of a point charge
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5
For Examiner’s Use Define the tesla. A horseshoe magnet is placed on a balance. A stiff metal wire is clamped horizontally between the poles, as illustrated in . balance pan horseshoe magnet stiff metal wire The magnetic flux density in the space between the poles of the magnet is uniform and is zero outside this region. The length of the metal wire normal to the magnetic field is 6.4 cm. When a current in the wire is switched on, the reading on the balance increases by 2.4 g. The current in the wire is 5.6 A. State and explain the direction of the force on the wire due to the current. For Examiner’s Use Calculate the magnitude of the magnetic flux density between the poles of the magnet. flux density = T A low frequency alternating current is now passed through the wire in . The root-mean-square (r.m.s.) value of the current is 5.6 A. Describe quantitatively the variation of the reading seen on the balance.
20. Magnetic fields  →  20.5. Electromagnetic induction
20. Magnetic fields  →  20.2. Force on a current-carrying conductor
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6
For Examiner’s Use Describe the main principles of the determination of the charge on an oil drop by Millikan’s experiment. You may draw a diagram if you wish. In an experiment to determine the fundamental charge, values of charge on oil drops were found by a student to be as shown below. 3.2 × 10–19 C; 6.4 × 10–19 C; 16 × 10–19 C; 9.7 × 10–19 C; 12.8 × 10–19 C; 3.1 × 10–19 C; 6.3 × 10–19 C. State the value, to two significant figures, of the fundamental charge that is suggested by these values of charge on oil drops. fundamental charge = C
9. Electricity  →  9.1. Electric current
18. Electric fields  →  18.5. Electric potential
11. Particle physics  →  11.2. Fundamental particles
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7
For Examiner’s Use The photoelectric effect may be represented by the equation photon energy = work function energy + maximum kinetic energy of electron. State what is meant by work function energy. The variation with frequency f of the maximum kinetic energy EK of photoelectrons emitted from the surface of sodium metal is shown in . 6.0 6.5 7.0 7.5 8.0 4.5 5.0 5.5 0.2 0.4 0.6 0.8 EK / eV f / 1014 Hz Use the gradient of the graph of to determine a value for the Planck constant h. Show your working. h = J s For Examiner’s Use The sodium metal in has a work function energy of 2.4 eV. The sodium is replaced by calcium which has a work function energy of 2.9 eV. On , draw a line to show the variation with frequency f of the maximum kinetic energy EK of photoelectrons emitted from the surface of calcium.
22. Quantum physics  →  22.2. Photoelectric effect
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8
For Examiner’s Use The element strontium has at least 16 isotopes. One of these isotopes is strontium-89. This isotope has a half-life of 52 days. State what is meant by isotopes. Calculate the probability per second of decay of a nucleus of strontium-89. probability = s–1 A laboratory prepares a strontium-89 source. The activity of this source is measured 21 days after preparation of the source and is found to be 7.4 × 106 Bq. Determine, for the strontium-89 source at the time that it was prepared, the activity, activity = Bq the mass of strontium-89. mass = g
23. Nuclear physics  →  23.2. Radioactive decay
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9
An operational amplifier (op-amp) may be used as part of the processing unit in an electronic sensor. State four properties of an ideal operational amplifier. 1. 2. 3. 4. A comparator circuit incorporating an ideal op-amp is shown in . – + +5 V –5 V VOUT VIN The variation with time t of the input potential VIN is shown in . –2 –6 –4 potential / V t VIN VIN On the axes of , draw a graph to show the variation with time t of the output potential VOUT . For Examiner’s Use The output potential VOUT is to be displayed using two light-emitting diodes (LEDs). A diode emitting red light is to indicate when VOUT is positive and a diode emitting green light is to be used to indicate when VOUT is negative. Complete to show the connections of the two LEDs to the output of the op-amp. Label each LED with the colour of light that it emits. VOUT
10. D.C. circuits  →  10.3. Potential dividers
10. D.C. circuits  →  10.1. Practical circuits
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10
For Examiner’s Use 10 An aluminium block is placed near to a small source of X-ray radiation, as shown in . A B aluminium block X-ray source X-rays from the source are detected at point A and at point B. State two reasons why the intensity of the X-ray beam at point B is not as great as the intensity at point A. 1. 2. A cross-section through a model of a finger is shown in . 2.4 cm 1.1 cm bone soft tissue D B C A The thickness of the model is 2.4 cm and that of the bone in the model is 1.1 cm. Parallel beams of X-rays are incident on the model in the directions AB and CD, as shown in . For Examiner’s Use Data for the linear attenuation coefficient μ for the bone and the soft tissue in the model are given in . μ / cm–1 bone soft tissue 3.00 0.27 Calculate the ratio intensity of X-ray beam incident on the model intensity of X-ray beam emergent from the model for the beam AB, ratio = the beam CD. ratio = Use your answers in to suggest why, for this model, an X-ray image with good contrast may be obtained.
24. Medical physics  →  24.2. Production and use of X-rays
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11
For Examiner’s Use 11 A signal that is transmitted over a long distance will be attenuated and it will pick up noise. State what is meant by attenuation, noise. Explain why regenerator amplifiers do not amplify the noise that has been picked up on digital signals. A transmitter on Earth produces a signal of power 2.4 kW. This signal, when received by a satellite, is attenuated by 195 dB. Calculate the signal power received by the satellite. power = W
24. Medical physics  →  24.2. Production and use of X-rays
8. Superposition  →  8.3. Interference
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12
For Examiner’s Use 12 An incomplete simplified block diagram of the circuitry for a mobile-phone handset is shown in . tuning circuit amplifier amplifier amplifier amplifier microphone loudspeaker Y DAC demodulator oscillator parallel- to-serial converter ADC X switch aerial State the name of the block labelled X, Y. Question 12 continues on page 24. For Examiner’s Use Explain the purpose of the switch, the parallel-to-serial converter.
10. D.C. circuits  →  10.1. Practical circuits
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