科目：物理 Physics (9702)
年份：2017 夏季
试卷：Paper 41
总页数：20
章节：12-13: Circular Motion & Gravitational Fields, 14-16: Temperature, Ideal Gases & Thermodynamics, 17: Oscillations, 18: Electric fields, 20: Magnetic fields, 21: Alternating currents, 22: Quantum physics, 23: Nuclear physics, 24: Medical physics
4 Answer all the questions in the spaces provided. 1 (a) Explain how a satellite may be in a circular orbit around a planet. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) 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 $\rho$ . The Moon, mass $m$ , is in a circular orbit about the Earth with radius $nR$ , as illustrated in Fig. 1.1. <div style="text-align: cen
5
(c) The radius $R$ of the Earth is $6.38 \times 10^3 \text{km}$ and the distance between the centre of the Earth and the centre of the Moon is $3.84 \times 10^5 \text{km}$ .
The period $T$ of the orbit of the Moon about the Earth is 27.3 days.
Use the expression in (b) to calculate $\rho$ .
$$
\rho = \underline{\hspace{5cm}} \text{ kg m}^{-3} \text{ [3]}
$$
[Total: 9]
© UCLES 2017 9702/41/M/J/17 [Turn over6 2 A bar magnet of mass 180 g is suspended from the free end of a spring, as illustrated in Fig. 2.1. Fig. 2.1 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 Fig. 2.2. Fig. 2.2 © UCLES 2017 9702/41/M/J/17
7 (a) Determine, to two significant figures, the frequency of oscillation of the magnet. frequency = ………………………………………… Hz [2] (b) State whether the closing of the switch gives rise to light, heavy or critical damping. ……………………………………………………………………………………………………… [1] (c) Calculate the change in the energy $\Delta E$ of oscillation of the magnet between time $t = 2.7$ s and time $t = 7.5$ s. Explain your working. $\Delta E = $ ………………………………………… J 6 © UCLES 2017 9702/41/M/J/17 [Turn over
8 3 The digital transmission of speech may be illustrated using the block diagram of Fig. 3.1. plaintext ○ → ▶ [ADC] → [X] → [optical fibre] → [serial-to-parallel converter] → [Y] → ▶ [喇叭] ``` Fig. 3.1 (a) (i) State what is meant by a *digital signal*. ............................................................................................................................... ............................................................................................................................... [1] (ii) State the names of the components labelled X and Y on Fig. 3.1. X: ............................................................................................................................... Y: ............................................................................
9 (ii) the noise power at the output of the optic fibre. noise power = ........................................ W 3 © UCLES 2017 9702/41/M/J/17 [Turn over
10 4 (a) Describe the motion of molecules in a gas, according to the kinetic theory of gases. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Describe what is observed when viewing Brownian motion that provides evidence for your answer in (a). ............................................................................................................................... .............................................................................
11
5 An $\alpha$ -particle is travelling in a vacuum towards the centre of a gold nucleus, as illustrated in Fig. 5.1.
<div style="display: flex; justify-content: space-between; width: 60%;">
<div style="text-align: center;">
gold nucleus<br>
○<br>
charge $79e$
</div>
<div style="text-align: center;">
$\alpha$ -particle<br>
← ●<br>
energy $7.7 \times 10^{-13}$ J
</div>
</div>
Fig. 5.1
The gold nucleus has charge $79e$ .
The gold nucleus and the $\alpha$ -particle may be assumed to behave as point charges.
At a large distance from the gold nucleus, the $\alpha$ -particle has energy $7.7 \times 10^{-13}$ J.
(a) The $\alpha$ -particle does not collide with the gold nucleus. Show that the radius of the gold nucleus must be less than $4.7 \times 10^{-14}$ m.
[3]
(b) Determine the ac12 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 Fig. 6.1. Fig. 6.1 (a) (i) A relay is required as part of the output device. This is not shown in Fig. 6.1. Explain why a relay is required. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ [2] (ii) On Fig. 6.1, draw the symbol for a relay connected in the circuit as part of the output device. [2]
13 (c) State whether the lamp will switch on as the light level increases or as it decreases. Explain your answer. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... 3 © UCLES 2017 9702/41/M/J/17 [Turn over
14 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 Fig. 7.1. <div style="text-align: center;">  <br/> <em>Fig. 7.1</em> </div> 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 $r$ . (a) Explain why the path of the electron in the magnetic field is the arc of a circle. ............................................................................................................................... .
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(c) The potential difference $V$ is $120\,\text{V}$ . The radius $r$ of the circular arc is $7.4\,\text{cm}$ .
Determine the magnitude $B$ of the magnetic flux density.
$$
B = \underline{\hspace{5cm}} \text{ T [3]}
$$
(d) The potential difference $V$ in (c) 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.
$\underline{\hspace{10cm}}$
$\underline{\hspace{10cm}}$
$\underline{\hspace{10cm}}$ [2]
[Total: 10]
© UCLES 2017 9702/41/M/J/17 [Turn over16 8 Explain the main principles behind the use of nuclear magnetic resonance imaging (NMRI) to obtain information about internal body structures. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ......
17 9 A simple transformer is illustrated in Fig. 9.1. <div style="text-align: center;">  <br/> Fig. 9.1 </div> (a) (i) State why the transformer has an iron core, rather than having no core. ............................................................................................................................... ............................................................................................................................... [1] (ii) Explain why the core is laminated. ............................................................................................................................... ............................................................................................................................... [2] (b) By refere
18 BLANK PAGE © UCLES 2017 9702/41/M/J/17
19 10 (a) State (i) what is meant by the *hardness* of an X-ray beam, ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) how the hardness of an X-ray beam from an X-ray tube is increased. ............................................................................................................................... ............................................................................................................................... [1] (
20 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 Fig. 11.1. <div style="text-align: center;">  </div> Fig. 11.1 (a) 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. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ...........
21 (i) 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 [2] (ii) Use data from (i) and your answer in (i) to show, on Fig. 11.2, the changes in energy levels giving rise to the dark lines in (a). 2 © UCLES 2017 9702/41/M/J/17 [Turn over
22
12 One possible nuclear reaction that takes place in a nuclear reactor is given by the equation
$$
{}^{235}_{92}\text{U} + {}^1_0\text{n} \rightarrow {}^{95}_{42}\text{Mo} + {}^{139}_{57}\text{La} + 2{}^1_0\text{n} + x{}^0_1\text{e}
$$
Data for the nuclei and particles are given in Fig. 12.1.
<table>
<tr>
<th>nucleus or particle</th>
<th>mass/u</th>
</tr>
<tr>
<td> ${}^{235}_{92}\text{U}$ </td>
<td>235.123</td>
</tr>
<tr>
<td> ${}^{95}_{42}\text{Mo}$ </td>
<td>94.945</td>
</tr>
<tr>
<td> ${}^{139}_{57}\text{La}$ </td>
<td>138.955</td>
</tr>
<tr>
<td> ${}^1_0\text{n}$ </td>
<td>1.00863</td>
</tr>
<tr>
<td> ${}^0_{-1}\text{e}$ </td>
<td> $5.49 \times 10^{-4}$ </td>
</tr>
</table>
Fig. 12.1
(a) Determine, for thi23
(b) (i) Show that the energy equivalent to $1.00\,\text{u}$ is $934\,\text{MeV}$ .
[3]
(ii) Calculate the energy, in MeV, released in this reaction. Give your answer to three significant figures.
energy = ………………………………………… MeV [3]
(c) Suggest the forms of energy into which the energy calculated in (b)(ii) is transformed.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
……………………………………………………………………………………………………… 2
© UCLES 2017 9702/41/M/J/17