9702_s07_qp_4
A paper of Physics, 9702
Questions:
11
Year:
2007
Paper:
4
Variant:
0
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1
Explain what is meant by a gravitational field. A spherical planet has mass M and radius R. The planet may be considered to have all its mass concentrated at its centre. A rocket is launched from the surface of the planet such that the rocket moves radially away from the planet. The rocket engines are stopped when the rocket is at a height R above the surface of the planet, as shown in . R R 2R planet The mass of the rocket, after its engines have been stopped, is m. Show that, for the rocket to travel from a height R to a height 2R above the planet’s surface, the change ΔEP in the magnitude of the gravitational potential energy of the rocket is given by the expression ΔEP = GMm 6R . Examiner’s Use During the ascent from a height R to a height 2R, the speed of the rocket changes from 7600 m s–1 to 7320 m s–1. Show that, in SI units, the change ΔEK in the kinetic energy of the rocket is given by the expression ΔEK = (2.09 × 106)m. The planet has a radius of 3.40 × 106 m. Use the expressions in to determine a value for the mass M of the planet. M = …………………………… kg State one assumption made in the determination in .
5. Work, energy and power  →  5.2. Gravitational potential energy and kinetic energy
13. Gravitational fields  →  13.4. Gravitational potential
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2
Use Use the kinetic theory of matter to explain why melting requires energy but there is no change in temperature. Define specific latent heat of fusion. A block of ice at 0 °C has a hollow in its top surface, as illustrated in . hollow ice A mass of 160 g of water at 100 °C is poured into the hollow. The water has specific heat capacity 4.20 kJ kg–1 K–1. Some of the ice melts and the final mass of water in the hollow is 365 g. Assuming no heat gain from the atmosphere, calculate a value, in kJ kg–1, for the specific latent heat of fusion of ice. specific latent heat = …………………………. kJ kg–1 Examiner’s Use In practice, heat is gained from the atmosphere during the experiment. This means that your answer to is not the correct value for the specific latent heat. State and explain whether your value in is greater or smaller than the correct value.
14. Temperature  →  14.3. Specific heat capacity and specific latent heat
16. Thermodynamics  →  16.2. The first law of thermodynamics
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3
Use Two charged points A and B are separated by a distance of 6.0 cm, as shown in . d 6.0 cm A B The variation with distance d from A of the electric field strength E along the line AB is shown in . d /cm E / kV m–1 position of A position of B An electron is emitted with negligible speed from A and travels along AB. State the relation between electric field strength E and potential V. Examiner’s Use The area below the line of the graph of represents the potential difference between A and B. Use to determine the potential difference between A and B. potential difference = …………………………. V Use your answer to to calculate the speed of the electron as it reaches point B. speed = …………………………. m s–1 Use to determine the value of d at which the electron has maximum acceleration. d = …………………… cm Without any further calculation, describe the variation with distance d of the acceleration of the electron.
18. Electric fields  →  18.5. Electric potential
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4
Use An ideal transformer has 5000 turns on its primary coil. It is to be used to convert a mains supply of 230 V r.m.s. to an alternating voltage having a peak value of 9.0 V. Calculate the number of turns on the secondary coil. number = ……………………………… The output from the transformer is to be full-wave rectified. shows part of the rectifier circuit. A B R On , draw diode symbols to complete the diagram of the rectifier such that terminal A of the resistor R is positive with respect to terminal B, the symbol for a capacitor connected to provide smoothing of the potential difference across the resistor R. Examiner’s Use shows the variation with time t of the smoothed potential difference V across the resistor R. V t1 t3 t4 t t2 State the interval of time during which the capacitor is being charged from the transformer. from time ………… to time …………… The resistance of the resistor R is doubled. On , sketch the variation with time t of the potential difference V across the resistor.
21. Alternating currents  →  21.2. Rectification and smoothing
19. Capacitance  →  19.3. Discharging a capacitor
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5
Use Explain what is meant by a photon. Show that the photon energy of light of wavelength 350 nm is 5.68 × 10–19 J. State the value of the ratio energy of photon of light of wavelength 700 nm energy of photon of light of wavelength 350 nm . ratio = …………… Two beams of monochromatic light have similar intensities. The light in one beam has wavelength 350 nm and the light in the other beam has wavelength 700 nm. The two beams are incident separately on three different metal surfaces. The work function of each of these surfaces is shown in . metal work function / eV tungsten magnesium potassium 4.49 3.68 2.26 Explain what is meant by the work function of the surface. Examiner’s Use State which combination, if any, of monochromatic light and metal surface could give rise to photo-electric emission. Give a quantitative explanation of your answer.
22. Quantum physics  →  22.2. Photoelectric effect
24. Medical physics  →  24.2. Production and use of X-rays
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6
Use Define the decay constant of a radioactive isotope. Strontium-90 is a radioactive isotope having a half-life of 28.0 years. Strontium-90 has a density of 2.54 g cm–3. A sample of Strontium-90 has an activity of 6.4 × 109 Bq. Calculate the decay constant λ, in s–1, of Strontium-90, λ = …………………………. s–1 the mass of Strontium-90 in the sample, mass = …………………………. g Examiner’s Use the volume of the sample. volume = …………………………. cm3 By reference to your answer in , suggest why dust that has been contaminated with Strontium-90 presents a serious health hazard.
23. Nuclear physics  →  23.2. Radioactive decay
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7
Use A magnet is suspended vertically from a fixed point by means of a spring, as shown in . spring coil magnet R One end of the magnet hangs inside a coil of wire. The coil is connected in series with a resistor R. The magnet is displaced vertically a small distance D and then released. shows the variation with time t of the vertical displacement d of the magnet from its equilibrium position. 0.2 0.4 0.6 0.8 1.0 1.2 1.4 +D –D d t /s Examiner’s Use State and explain, by reference to electromagnetic induction, the nature of the oscillations of the magnet. Calculate the angular frequency ω0 of the oscillations. ω0 = …………….……………… rad s–1 The resistance of the resistor R is increased. The magnet is again displaced a vertical distance D and released. On , sketch the variation with time t of the displacement d of the magnet. Examiner’s Use The resistor R in is replaced by a variable-frequency signal generator of constant r.m.s. output voltage. The angular frequency ω of the generator is gradually increased from about 0.7ω0 to about 1.3ω0, where ω0 is the angular frequency calculated in . On the axes of , sketch a graph to show the variation with ω of the amplitude A of the oscillations of the magnet. A 0.7 0 1.0 0 1.3 0 ω ω ω ω State the name of the phenomenon illustrated in the graph of . Briefly describe one situation where the phenomenon named in is useful and one situation where it should be avoided. useful: avoid:
20. Magnetic fields  →  20.5. Electromagnetic induction
17. Oscillations  →  17.1. Simple harmonic oscillations
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8
State three characteristics of an ideal operational amplifier (op-amp). 1. 2. 3. An amplifier circuit for a microphone is shown in . 120 kΩ X V OUT R + – Name the type of feedback used with this op-amp. The output potential difference VOUT is 5.8 V for a potential difference across the resistor R of 69 mV. Calculate 1. the gain of the amplifier circuit, gain = ……………………… Examiner’s Use 2. the resistance of resistor X. resistance = ……………………… Ω State one effect on the amplifier output of reducing the resistance of resistor X.
10. D.C. circuits  →  10.1. Practical circuits
10. D.C. circuits  →  10.3. Potential dividers
9. Electricity  →  9.3. Resistance and resistivity
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10
Use 10 An analogue signal is sampled at a frequency of 5.0 kHz. Each sample is converted into a four-bit number and transmitted as a digital signal. shows part of the digital signal. 0010 0101 1010 1111 0100 0010 0101 1010 1111 0100 most significant bit START The digital signal is transmitted and is finally converted into an analogue signal. On the axes of , sketch a graph to show the variation with time t of this final analogue signal. 0.2 signal 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 t /ms 2.0 Suggest two ways in which the reproduction of the original analogue signal could be improved. 1. 2.
17. Oscillations  →  17.1. Simple harmonic oscillations
8. Superposition  →  8.2. Diffraction
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