9702_w20_qp_41
A paper of Physics, 9702
Questions:
12
Year:
2020
Paper:
4
Variant:
1
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1
State what is meant by a field of force. Define gravitational field strength. An isolated planet may be assumed to be a uniform sphere of radius 3.39 × 106 m with its mass of 6.42 × 1023 kg concentrated at its centre. Calculate the gravitational field strength at the surface of the planet. field strength = N kg–1 Calculate the height above the surface of the planet in at which the gravitational field strength is 1.0% less than its value at the surface of the planet. height = m
13. Gravitational fields  →  13.3. Gravitational field of a point mass
13. Gravitational fields  →  13.4. Gravitational potential
13. Gravitational fields  →  13.1. Gravitational field
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2
The first law of thermodynamics may be expressed as ΔU = (+q) + (+w) where ΔU is the increase in internal energy of the system. State the meaning of: +q +w. The variation with pressure p of the volume V of a fixed mass of an ideal gas is shown in . 2.2 2.0 2.4 2.8 3.2 3.6 V / 10–3 m3 p / 105 Pa 4.0 2.6 3.0 3.4 3.8 4.2 4.6 5.0 5.4 A C B The gas undergoes a cycle of changes A to B to C to A. During the change A to B, the volume of the gas increases from 2.3 × 10–3 m3 to 3.8 × 10–3 m3. Show that the magnitude of the work done during the change A to B is 390 J. State and explain the total change, if any, in the internal energy of the gas during one complete cycle. During the change A to B, 1370 J of thermal energy is transferred to the gas. During the change B to C, no thermal energy enters or leaves the gas. The work done on the gas during this change is 550 J. Use these data and the information in to complete Table 2.1. Table 2.1 change q / J w / J ΔU / J A to B B to C C to A
16. Thermodynamics  →  16.2. The first law of thermodynamics
15. Ideal gases  →  15.2. Equation of state
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3
A pendulum consists of a metal sphere P suspended from a fixed point by means of a thread, as illustrated in . metal sphere P thread L x The centre of gravity of sphere P is a distance L from the fixed point. The sphere is pulled to one side and then released so that it oscillates. The sphere may be assumed to oscillate with simple harmonic motion. State what is meant by simple harmonic motion. The variation of the velocity v of sphere P with the displacement x from its mean position is shown in . 0.1 0.2 0.3 –0.3 –0.2 –0.1 –2 –4 –6 –8 –10 v / m s–1 x / cm Use to determine the frequency f of the oscillations of sphere P. f = Hz The period T of the oscillations of sphere P is given by the expression T = 2π g L c m where g is the acceleration of free fall. Use your answer in to determine the length L. L = m Another pendulum consists of a sphere Q suspended by a thread. Spheres P and Q are identical. The thread attached to sphere Q is longer than the thread attached to sphere P. Sphere Q is displaced and then released. The oscillations of sphere Q have the same amplitude as the oscillations of sphere P. On , sketch the variation of the velocity v with displacement x for sphere Q.
17. Oscillations  →  17.1. Simple harmonic oscillations
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5
Define electric potential at a point. Two point charges A and B are separated by a distance of 12.0 cm in a vacuum, as illustrated in . charge A P charge B 12.0 cm x The charge of A is +2.0 × 10–9 C. A point P lies on the line joining charges A and B. Its distance from charge A is x. The variation with distance x of the electric potential V at point P is shown in . –40 –30 –20 –10 V / 102 V x / cm Use to determine: the charge of B charge = C the change in electric potential when point P moves from the position where x = 9.0 cm to the position where x = 3.0 cm. change = V An α-particle moves along the line joining point charges A and B in . The α-particle moves from the position where x = 9.0 cm and just reaches the position where x = 3.0 cm. Use your answer in to calculate the speed v of the α-particle at the position where x = 9.0 cm. v = m s–1
18. Electric fields  →  18.5. Electric potential
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7
An ideal operational amplifier (op-amp) is to be used in a comparator circuit. Part of the comparator circuit is shown in . – + VOUT +5.0 V –5.0 V Three resistors, each of resistance 1000 Ω, and a negative temperature coefficient thermistor are available to complete the circuit. The circuit is to be designed so that, at low temperatures, the output VOUT is –5.0 V and at higher temperatures, the output VOUT is to be +5.0 V. On , draw the input circuit to the inverting and non-inverting inputs of the op-amp. State a suitable value for the thermistor resistance when the thermistor is at: low temperature where VOUT is –5.0 V a higher temperature where VOUT is +5.0 V.
9. Electricity  →  9.3. Resistance and resistivity
10. D.C. circuits  →  10.3. Potential dividers
10. D.C. circuits  →  10.1. Practical circuits
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8
A slice of a conducting material has its face QRLK normal to a uniform magnetic field of flux density B, as illustrated in . direction of movement of electrons magnetic flux density B K Q M P S R L J Electrons enter the slice travelling perpendicular to face PQKJ. For the free electrons moving in the slice: state the direction of the force on an electron due to movement of the electron in the magnetic field identify the faces, using the letters on , between which a potential difference is developed. face and face Explain why the potential difference in reaches a maximum value. The number of free electrons per unit volume in the slice of material is 1.3 × 1029 m–3. The thickness PQ of the slice is 0.10 mm. The magnetic flux density B is 4.6 × 10–3 T. Calculate the potential difference across the slice for a current of 6.3 × 10–4 A. potential difference = V The slice in is a metal. By reference to your answer in , suggest why Hall probes are usually made using semiconductors rather than metals.
20. Magnetic fields  →  20.3. Force on a moving charge
20. Magnetic fields  →  20.4. Magnetic fields due to currents
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9
Define magnetic flux. A simple transformer consists of two coils of wire wound on a soft-iron core, as illustrated in . soft-iron core secondary coil primary coil There is a sinusoidal current in the primary coil. Explain: how this current gives rise to an induced electromotive force (e.m.f.) in the secondary coil why the e.m.f. induced in the secondary coil is not constant. Explain why the soft-iron core in is laminated.
20. Magnetic fields  →  20.4. Magnetic fields due to currents
20. Magnetic fields  →  20.5. Electromagnetic induction
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10
Outline briefly the principles of computed tomography (CT scanning). One section of a model designed to illustrate CT scanning is divided into four voxels. The pixel numbers K, L, M and N of the voxels are shown in . K L D1 D2 D3 D4 N M The section is viewed, in turn, from four different directions D1, D2, D3 and D4, as shown in . The detector readings for each direction are noted and these are summed to give the values shown in . The background reading is 24. Determine the pixel numbers K, L, M and N shown in . K = L = M = N =
24. Medical physics  →  24.2. Production and use of X-rays
24. Medical physics  →  24.3. PET scanning
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11
A photon of wavelength 540 nm collides with an isolated stationary electron, as illustrated in . electron incident photon wavelength 540 nm deflected photon wavelength 544 nm The photon is deflected elastically by the electron. The wavelength of the deflected photon is 544 nm. State what is meant by a photon. On , draw an arrow to indicate the approximate direction of motion of the deflected electron. Calculate: the momentum of the deflected photon momentum = N s the energy transferred to the deflected electron. energy = J Another photon of wavelength 540 nm collides with an isolated stationary electron. Explain why it is not possible for the deflected photon to have a wavelength less than 540 nm.
22. Quantum physics  →  22.1. Energy and momentum of a photon
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12
To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. 12 Iodine-131 (131 53 is a radioactive isotope with a decay constant of 9.9 × 10–7 s–1. State what is meant by: radioactive decay constant. Some water becomes contaminated with iodine-131. The activity of the iodine-131 in 1.0 kg of water is 560 Bq. Determine the number of iodine-131 atoms in 1.0 kg of water. number = Regulations require that the activity of iodine-131 in 1.0 kg of water is to be less than 170 Bq. Calculate the time, in days, for the activity of the contaminated water in to be reduced to 170 Bq. time = days
23. Nuclear physics  →  23.2. Radioactive decay
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