9702_s17_qp_43
A paper of Physics, 9702
Questions:
12
Year:
2017
Paper:
4
Variant:
3
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1
Explain how a satellite may be in a circular orbit around a planet. The Earth and the Moon may be considered to be uniform spheres that are isolated in space. The Earth has radius R and mean density ρ. The Moon, mass m, is in a circular orbit about the Earth with radius nR, as illustrated in . Moon Earth radius R nR The Moon makes one complete orbit of the Earth in time T. Show that the mean density ρ of the Earth is given by the expression ρ = 3πn3 GT 2 . The radius R of the Earth is 6.38 × 103 km and the distance between the centre of the Earth and the centre of the Moon is 3.84 × 105 km. The period T of the orbit of the Moon about the Earth is 27.3 days. Use the expression in to calculate ρ. ρ = kg m–3
13. Gravitational fields  →  13.2. Gravitational force between point masses
13. Gravitational fields  →  13.3. Gravitational field of a point mass
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2
A bar magnet of mass 180 g is suspended from the free end of a spring, as illustrated in . spring magnet coil The magnet hangs so that one pole is near the centre of a coil of wire. The coil is connected in series with a resistor and a switch. The switch is open. The magnet is displaced vertically and then allowed to oscillate with one pole remaining inside the coil. The other pole remains outside the coil. At time t = 0, the magnet is oscillating freely as it passes through its equilibrium position. At time t = 3.0 s, the switch in the circuit is closed. The variation with time t of the vertical displacement y of the magnet is shown in . –2.0 –1.5 –1.0 –0.5 0.5 1.0 y / cm 1.5 2.0 t / s Determine, to two significant figures, the frequency of oscillation of the magnet. frequency = Hz State whether the closing of the switch gives rise to light, heavy or critical damping. Calculate the change in the energy ΔE of oscillation of the magnet between time t = 2.7 s and time t = 7.5 s. Explain your working. ΔE = J
17. Oscillations  →  17.3. Damped and forced oscillations, resonance
17. Oscillations  →  17.1. Simple harmonic oscillations
6. Deformation of solids  →  6.1. Stress and strain
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3
The digital transmission of speech may be illustrated using the block diagram of . ADC serial -to - parallel converter optic fibre X Y State what is meant by a digital signal. State the names of the components labelled X and Y on . X: Y: Describe the function of the ADC. The optic fibre has length 84 km and the attenuation per unit length in the fibre is 0.19 dB km–1. The input power to the optic fibre is 9.7 mW. At the output from the optic fibre, the signal-to- noise ratio is 28 dB. Calculate in dB, the ratio input power to optic fibre noise power at output of optic fibre, ratio = dB the noise power at the output of the optic fibre. noise power = W
24. Medical physics  →  24.1. Production and use of ultrasound
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4
Describe the motion of molecules in a gas, according to the kinetic theory of gases. Describe what is observed when viewing Brownian motion that provides evidence for your answer in . At a pressure of 1.05 × 105 Pa and a temperature of 27 °C, 1.00 mol of helium gas has a volume of 0.0240 m3. The mass of 1.00 mol of helium gas, assumed to be an ideal gas, is 4.00 g. Calculate the root-mean-square (r.m.s.) speed of an atom of helium gas for a temperature of 27 °C. r.m.s. speed = m s–1 Using your answer in , calculate the r.m.s. speed of the atoms at 177 °C. r.m.s. speed = m s–1
15. Ideal gases  →  15.3. Kinetic theory of gases
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5
An α-particle is travelling in a vacuum towards the centre of a gold nucleus, as illustrated in . gold nucleus α-particle charge 79e energy 7.7 10–13 J × The gold nucleus has charge 79e. The gold nucleus and the α-particle may be assumed to behave as point charges. At a large distance from the gold nucleus, the α-particle has energy 7.7 × 10–13 J. The α-particle does not collide with the gold nucleus. Show that the radius of the gold nucleus must be less than 4.7 × 10–14 m. Determine the acceleration of the α-particle for a separation of 4.7 × 10–14 m between the centres of the gold nucleus and of the α-particle. acceleration = m s–2 In an α-particle scattering experiment, the beam of α-particles is incident on a very thin gold foil. Suggest why the gold foil must be very thin.
11. Particle physics  →  11.1. Atoms, nuclei and radiation
20. Magnetic fields  →  20.3. Force on a moving charge
24. Medical physics  →  24.2. Production and use of X-rays
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6
A comparator circuit is designed to switch on a mains lamp when the ambient light level reaches a set value. An incomplete diagram of the circuit is shown in . – + +5 V –5 V D RV 6 V A relay is required as part of the output device. This is not shown in . Explain why a relay is required. On , draw the symbol for a relay connected in the circuit as part of the output device. Describe the function of the variable resistor RV, the diode D. State whether the lamp will switch on as the light level increases or as it decreases. Explain your answer.
10. D.C. circuits  →  10.3. Potential dividers
10. D.C. circuits  →  10.1. Practical circuits
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7
An electron having charge –q and mass m is accelerated from rest in a vacuum through a potential difference V. The electron then enters a region of uniform magnetic field of magnetic flux density B, as shown in . path of electron uniform magnetic field into plane of paper The direction of the uniform magnetic field is into the plane of the paper. The velocity of the electron as it enters the magnetic field is normal to the magnetic field. The radius of the circular path of the electron in the magnetic field is r. Explain why the path of the electron in the magnetic field is the arc of a circle. Show that the magnitude p of the momentum of the electron as it enters the magnetic field is given by p = (2mqV ). The potential difference V is 120 V. The radius r of the circular arc is 7.4 cm. Determine the magnitude B of the magnetic flux density. B = T The potential difference V in is increased. The magnetic flux density B remains unchanged. By reference to the momentum of the electron, explain the effect of this increase on the radius r of the path of the electron in the magnetic field.
20. Magnetic fields  →  20.3. Force on a moving charge
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10
State what is meant by the hardness of an X-ray beam, how the hardness of an X-ray beam from an X-ray tube is increased. The same parallel beam of X-ray radiation is incident, separately, on samples of bone and of muscle. Data for the thickness x of the samples of bone and of muscle, together with the linear attenuation coefficients μ of the radiation in bone and in muscle, are given in Fig. 10.1. x / cm μ / cm–1 bone 1.5 2.9 muscle 4.0 0.95 Determine the ratio intensity transmitted through bone intensity transmitted through muscle . ratio =
24. Medical physics  →  24.2. Production and use of X-rays
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11
A beam of light consists of a continuous range of wavelengths from 420 nm to 740 nm. The light passes through a cloud of cool gas, as shown in . incident light cool gas emergent light wavelengths 420 nm – 740 nm The spectrum of the light emerging from the cloud of cool gas is viewed using a diffraction grating. Explain why this spectrum contains a number of dark lines. Some of the electron energy levels of the atoms in the cloud of gas are represented in . energy – 0.38 eV – 0.54 eV – 0.85 eV – 1.5 eV – 3.4 eV – 13.6 eV (not to scale) Light of wavelength 420 nm has a photon energy of 2.96 eV. Calculate the photon energy, in eV, of light of wavelength 740 nm. photon energy = eV Use data from and your answer in to show, on , the changes in energy levels giving rise to the dark lines in .
22. Quantum physics  →  22.4. Energy levels in atoms and line spectra
22. Quantum physics  →  22.1. Energy and momentum of a photon
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12
One possible nuclear reaction that takes place in a nuclear reactor is given by the equation 92U + 1 0n 42Mo + 139 57La + 21 0n + x 0 –1e Data for the nuclei and particles are given in . nucleus or particle mass / u 92U 235.123 42Mo 94.945 57La 138.955 0n 1.00863 –1e 5.49 × 10–4 Determine, for this nuclear reaction, the value of x. x = Show that the energy equivalent to 1.00 u is 934 MeV. Calculate the energy, in MeV, released in this reaction. Give your answer to three significant figures. energy = MeV Suggest the forms of energy into which the energy calculated in is transformed.
23. Nuclear physics  →  23.1. Mass defect and nuclear binding energy
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