科目：物理 Physics (9702)
年份：2019 春季
试卷：Paper 42
总页数：20
章节：12-13: Circular Motion & Gravitational Fields, 14-16: Temperature, Ideal Gases & Thermodynamics, 17: Oscillations, 18: Electric fields, 19: Capacitance, 20: Magnetic fields, 21: Alternating currents, 22: Quantum physics, 23: Nuclear physics, 24: Medical physics
4 https://www.edutvonline.com Answer all the questions in the spaces provided. 1 (a) (i) Define gravitational potential at a point. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) Use your answer in (i) to explain why the gravitational potential near an isolated mass is always negative. ............................................................................................................................... ..............................
5 (ii) calculate its gravitational potential energy. energy = ………………………………………… J [3] (c) Rockets on the satellite are fired for a short time. The satellite’s orbit is now closer to the surface of the planet. State and explain the change, if any, in the kinetic energy of the satellite. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………… 2 © UCLES 2019 9702/42/F/M/19 [Turn over https://www.edutvonline.com
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2 The pressure $p$ of an ideal gas having density $\rho$ is given by the expression
$$
p = \frac{1}{3} \rho \langle c^2 \rangle.
$$
(a) State what is meant by:
(i) an ideal gas
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(ii) the symbol $\langle c^2 \rangle$ .
...............................................................................................................................
..........................7 https://www.edutvonline.com (iii) One of the assumptions of the kinetic theory of gases is related to the volume of the atoms. State this assumption. Explain whether your answer in (ii) is consistent with this assumption. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... 2 © UCLES 2019 9702/42/F/M/19 [Turn over
8 https://www.edutvonline.com 3 A cylindrical tube, sealed at one end, has cross-sectional area $A$ and contains some sand. The total mass of the tube and the sand is $M$ . The tube floats upright in a liquid of density $\rho$ , as illustrated in Fig. 3.1.  Fig. 3.1 The tube is pushed a short distance into the liquid and then released. (a) (i) State the two forces that act on the tube immediately after its release. ............................................................................................................................ [1] (ii) State and explain the direction of the resultant force acting on the tube immediately after its release. ...............................................................................................................
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(c) For a tube having cross-sectional area $A$ of $4.5 \, \text{cm}^2$ and a total mass $M$ of $0.17 \, \text{kg}$ , the period of oscillation of the tube is $1.3 \, \text{s}$ .
(i) Determine the angular frequency $\omega$ of the oscillations.
$$
\omega = \underline{\hspace{5cm}} \, \text{rad} \, \text{s}^{-1} \, [2]
$$
(ii) Use your answer in (i) and the expression in (b) to determine the density $\rho$ of the liquid in which the tube is floating.
$$
\rho = \underline{\hspace{5cm}} \, \text{kg} \, \text{m}^{-3} \, [3]
$$
[Total: 10]
© UCLES 2019 9702/42/F/M/19 [Turn over10 https://www.edutvonline.com 4 (a) State three features of the orbit of a geostationary satellite. 1. ............................................................................................................................... 2. ............................................................................................................................... 3. ............................................................................................................................... [3] (b) A signal is transmitted from Earth to a geostationary satellite. Initially, the signal has power 3.2 kW. The signal is attenuated by 194 dB. Calculate the signal power received by the satellite. power = ................................................... W [2] (c) Suggest one advantage a
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5 (a) State what is meant by an *electric field*.
........................................................................................................................... [1]
(b) An isolated solid metal sphere has radius $R$ . The charge on the sphere is $+Q$ and the electric field strength at its surface is $E$ .
On Fig. 5.1, draw a line to show the variation of the electric field strength with distance $x$ from the centre of the solid sphere for values of $x$ from $x = 0$ to $x = 3R$ .
Fig. 5.1
[4]
(c) The sphere in (b) has radius $R = 0.26\,\text{m}$ .
Electrical breakdown (a spark) occurs when the electric field strength at the surface of the sphere exceeds $2.0 \times 10^6\,\text{V}\,\text{m}^{-1}$ .
Determine the maxi12
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6 (a) Define the *capacitance* of a parallel-plate capacitor.
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(b) A student has three capacitors. Two of the capacitors have a capacitance of $4.0\,\mu\mathrm{F}$ and one has a capacitance of $8.0\,\mu\mathrm{F}$ .
Draw labelled circuit diagrams, one in each case, to show how the three capacitors may be connected to give a total capacitance of:
(i) $1.6\,\mu\mathrm{F}$
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(c) A capacitor C of capacitance $47\,\mu\text{F}$ is connected across the output terminals of a bridge rectifier, as shown in Fig. 6.1.
<div style="text-align: center;">
</div>
Fig. 6.1
The variation with time $t$ of the potential difference $V$ across the resistor R is shown in Fig. 6.2.
<div style="text-align: center;">
</div>
Fig. 6.2
Use data from Fig. 6.2 to determine the energy transfer from the capacitor C to the resistor R between time $t_1$ and time $t_2$ .
energy = ………………………………………… J 3
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Note: The actual images (Fig. 6.1 and Fig. 6.2) are represented as placeholders since the original image content cannot be rendered in Markdown. In a real implementation14 https://www.edutvonline.com 7 (a) Two properties that an ideal operational amplifier (op-amp) would have are constant voltage gain and infinite slew rate. State what is meant by: (i) *gain of an amplifier* ........................................................................................................................... [1] (ii) *infinite slew rate.* ........................................................................................................................... [2] (b) The partially completed circuit of a non-inverting amplifier, incorporating an ideal op-amp, is shown in Fig. 7.1. Fig. 7.1 (i) On Fig. 7.1, complete the circuit for the non-inverting amplifier. [2] (ii) For the completed circuit of Fig. 7.1, the gain of the amplifier is 25. The resistance of
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(iii) Calculate, for the amplifier gain of 25, the range of values of $V_{IN}$ for which the amplifier does not saturate.
range from ……………… V to ……………… V 2
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Note: The document contains no tables or complex equations beyond the simple inline formula $V_{IN}$, which is rendered in LaTeX inline math mode. All text and structure have been preserved as requested.16 https://www.edutvonline.com 8 A horseshoe magnet is placed on a top pan balance. A rigid copper wire is fixed between the poles of the magnet, as illustrated in Fig. 8.1.  Fig. 8.1 The wire is clamped at ends A and B. (a) When a direct current is switched on in the wire, the reading on the balance is seen to decrease. State and explain the direction of: (i) the force acting on the wire ............................................................................................................................... ............................................................................................................................... ........................................................................................................................
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(b) A direct current of 4.6A in the wire causes the reading on the balance to change by $4.5 \times 10^{-3} \, \text{N}$ .
The direct current is now replaced by an alternating current of frequency 40Hz and root-mean-square (r.m.s.) value 4.6A.
On the axes of Fig. 8.2, sketch a graph to show the change in balance reading over a time of 50ms.
Fig. 8.2
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Note: The image content (graph) is represented as a placeholder comment since Markdown does not support direct image embedding with coordinates. The graph is described in the text as "Fig. 8.2" with axes labeled "change in balance reading / $10^{-3} \, \text{N}$ " (y-axis) and "time/ms" (x-axis), ranging from 0 to 50 on both axes. The graph is18 https://www.edutvonline.com BLANK PAGE © UCLES 2019 9702/42/F/M/19
19 https://www.edutvonline.com 9 Outline the principles of computed tomography (CT) scanning. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ..........................................................
20 https://www.edutvonline.com 10 (a) A cross-section through a current-carrying solenoid is shown in Fig. 10.1. current into page current out of page Fig. 10.1 On Fig. 10.1, draw field lines to represent the magnetic field inside the solenoid. [3] (b) State Faraday’s law of electromagnetic induction. [2] (c) A coil of insulated wire is wound on to a soft-iron core. The coil is connected in series with a battery, a switch and an ammeter, as shown in Fig. 10.2. coil of wire soft-iron core A Fig. 10.2 © UCLES 2019 9702/42/F/M/19
21 https://www.edutvonline.com Use laws of electromagnetic induction to explain why, when the switch is closed, the current increases *gradually* to its maximum value. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... 3 © UCLES 2019 9702/42/F/M/19 [Turn over
22 https://www.edutvonline.com 11 (a) State what is meant by a photon. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Calculate the energy, in eV, of a photon of light of wavelength 540 nm. energy = ................................................... eV [3] (c) The outermost electron energy bands of a semiconductor material are illustrated in Fig. 11.1. <div style="display: flex; align-items: center; gap: 10px;"> <div style="width: 150px; h
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12 The incomplete nuclear equation for one possible reaction that takes place in the core of a nuclear reactor is
$$
{}^{235}_{92}\text{U} + {}^{1}_{0}\text{n} \rightarrow {}^{139}_{57}\text{La} + {}^{85}_{42}\text{Mo} + 2\,{}^{1}_{0}\text{n} + \ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldots\ldot