科目：物理 Physics (9702)
年份：2017 夏季
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
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Answer all the questions in the spaces provided.
1 (a) Define gravitational field strength.
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............................................................................................................................... [1]
(b) The mass of a spherical comet of radius 3.6 km is approximately $1.0 \times 10^{13}$ kg.
(i) Assuming that the comet has constant density, calculate the gravitational field strength on the surface of the comet.
field strength = ........................................... N kg⁻¹ [2]
(ii) A probe having a weight of 960 N on Earth lands on the comet.
Using your answer in (i), determine the weight of the probe on the surface of the 5 (c) A second comet has a length of approximately 4.5 km and a width of approximately 2.6 km. Its outline is illustrated in Fig. 1.1. Fig. 1.1 Suggest one similarity and one difference between the gravitational fields at the surface of this comet and at the surface of the comet in (b). similarity: ....................................................................................................................... ....................................................................................................................... difference: ................................................................................................................... ....................................................................................................................... 2 ©
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2 (a) The pressure $p$ and volume $V$ of an ideal gas are related to the density $\rho$ of the gas by the expression
$$
p = \frac{1}{3} \rho \langle c^2 \rangle.
$$
(i) State what is meant by the symbol $\langle c^2 \rangle$ .
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............................................................................................................................... [1]
(ii) Use the expression to show that the mean kinetic energy $E_K$ of a gas molecule is given by
$$
E_K = \frac{3}{2} kT
$$
where $k$ is the Boltzmann constant and $T$ is the thermodynamic temperature.
[3]
(b) (i) An ideal gas containing 1.0 mol of molecules is heated at constant volume. Use the expr7
(ii) Nitrogen may be assumed to be an ideal gas. The molar mass of nitrogen gas is $28 \, \text{g} \, \text{mol}^{-1}$ . Use the answer in (b)(i) to calculate a value for the specific heat capacity, in $\text{J} \, \text{kg}^{-1} \, \text{K}^{-1}$ , at constant volume for nitrogen.
specific heat capacity = ……………………………… $\text{J} \, \text{kg}^{-1} \, \text{K}^{-1}$ 2
© UCLES 2017 9702/42/M/J/17 [Turn over8 3 A bar magnet of mass 250 g is suspended from the free end of a spring, as illustrated in Fig. 3.1. Fig. 3.1 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 $t = 6.0$ s, the switch in the circuit is closed. © UCLES 2017 9702/42/MJ/17
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The variation with time $t$ of the vertical displacement $y$ of the magnet is shown in Fig. 3.2.
Fig. 3.2
(a) For the oscillating magnet, use data from Fig. 3.2 to calculate, to two significant figures,
(i) the frequency $f$ ,
$$
f = \underline{\hspace{5cm}} \text{ Hz [2]}
$$
(ii) the energy of the oscillations during the time $t = 0$ to time $t = 6.0$ s.
$$
\text{energy} = \underline{\hspace{5cm}} \text{ J [3]}
$$
© UCLES 2017 9702/42/M/J/17 [Turn over10
(b) (i) State Faraday’s law of electromagnetic induction.
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(ii) Use Faraday’s law and energy conservation to explain why the amplitude of the oscillations of the magnet reduces after time $t = 6.0\,\text{s}$ .
.................................................................11 4 (a) Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ......................
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(b) A parallel beam of ultrasound has intensity $I_0$ as it enters a muscle of thickness 4.6 cm, as illustrated in Fig. 4.1.
<div style="text-align: center;">
<br/>
Fig. 4.1
</div>
The intensity of the beam just before it leaves the muscle is $I_T$ .
The ratio $I_0/I_T$ is found to be 2.9.
Calculate the linear attenuation (absorption) coefficient $\mu$ of the ultrasound in the layer of muscle.
$$
\mu = \underline{\hspace{5cm}} \text{ cm}^{-1} \text{ [3]}
$$
[Total: 9]
© UCLES 2017 9702/42/M/J/1713 5 (a) State two advantages of the transmission of data in digital form rather than in analogue form. 1. ............................................................................................................................... 2. ............................................................................................................................... [2] (b) An analogue signal $S_I$ is converted into a digital signal D using an analogue-to-digital converter (ADC). After transmission of the digital signal, it is converted back to an analogue signal $S_T$ using a digital-to-analogue converter (DAC), as illustrated in Fig. 5.1. plaintext analogue signal ADC digital signal DAC analogue signal S_I → D → S_T ``` Fig.
14 6 (a) State Coulomb’s law. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Two charged metal spheres A and B are situated in a vacuum, as illustrated in Fig. 6.1. <div style="text-align: center;">  </div> Fig. 6.1 The shortest distance between the surfaces of the spheres is 6.0 cm. A movable point P lies along the line joining the centres of the two spheres, a distance $x$ from the surface of sphere A. The variation
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(i) Use Fig. 6.2 to explain whether the two spheres have charges of the same, or opposite, sign.
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(ii) A proton is at point P where $x = 5.0 \, \text{cm}$ .
Use data from Fig. 6.2 to determine the acceleration of the proton.
acceleration = .................................16 7 A capacitor consists of two parallel metal plates, separated by an insulator, as shown in Fig. 7.1. <div style="text-align: center;">  <br/> Fig. 7.1 </div> (a) Suggest why, when the capacitor is connected across the terminals of a battery, the capacitor stores energy, not charge. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Define the *capacitance* of the capacitor. ...........................................
17 8 A student designs a circuit incorporating an operational amplifier (op-amp) as shown in Fig. 8.1. Fig. 8.1 (a) (i) On Fig. 8.1, draw a circle around the output device. [1] (ii) State the purpose of this circuit. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) The resistors X and Y each have resistance $R$. When conducting, the LED labelled B emits blue light and the LED labelled G emits green light. (i) State whether blue light or green l
18 (ii) State and explain what is observed as the resistance of component C is reduced. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [3] (c) Suggest the function of the variable resistor. .........
19 9 A Hall probe is placed near to one end of a current-carrying solenoid, as shown in Fig. 9.1.  Fig. 9.1 The probe is rotated about the axis XY and is then held in a position so that the Hall voltage is maximum. (a) Explain why (i) a Hall probe is made from a *thin slice* of material, ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) in order for consistent measurements of magnetic flux density to be made, the current i
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(b) The probe is now rotated through an angle of $360^\circ$ about the axis XY.
At angle $\theta = 0$ , the Hall voltage $V_H$ has maximum value $V_{MAX}$ .
On Fig. 9.2, sketch the variation with angle $\theta$ of the Hall voltage $V_H$ for one complete revolution of the probe about axis XY.
<div style="text-align: center;">
<br/>
Fig. 9.2
</div>
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10 (a) Briefly describe two phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light.
1. ...............................................................................................................................
2. ...............................................................................................................................
[2]
(b) The21
(ii) The variation with $\frac{1}{\lambda}$ of $E_{\text{MAX}}$ for the metal surface is shown in Fig. 10.1.
Fig. 10.1
1. Use Fig. 10.1 to determine the magnitude of $\lambda_0$ .
$\lambda_0 = \underline{\hspace{5cm}} \text{ m [1]}$
2. Use the gradient of Fig. 10.1 to determine a value for the Planck constant $h$ .
$h = \underline{\hspace{5cm}} \text{ Js [3]}$
(c) The metal surface in (b) becomes oxidised.
Photoelectric emission is still observed but the work function energy is increased.
On Fig. 10.1, draw a line to show the variation with $\frac{1}{\lambda}$ of $E_{\text{MAX}}$ for the oxidised surface. 2
© UCLES 2017 9702/42/M/J/17 [Turn over22
11 An electron has charge $-q$ and mass $m$ . It is accelerated from rest in a vacuum through a potential difference $V$ .
(a) Show that the momentum $p$ of the accelerated electron is given by
$$
p = \sqrt{2mqV}.
$$
[2]
(b) The potential difference $V$ through which the electron is accelerated is 120 V.
(i) State what is meant by the *de Broglie wavelength*.
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(ii) Calculate the de Broglie wavelen23
12 One nuclear reaction that can take place in a nuclear reactor may be represented, in part, by the equation
$$
{}^{235}_{92}\text{U} + {}^1_0\text{n} \rightarrow {}^{95}_{42}\text{Mo} + {}^{139}_{57}\text{La} + 2{}_^1_0\text{n} + \ldots\ldots\ldots + \text{energy}
$$
Data for a nucleus and some particles are given in Fig. 12.1.
<table>
<tr>
<th>nucleus or particle</th>
<th>mass/u</th>
</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> ${}^1_1\text{p}$ </td>
<td>1.00728</td>
</tr>
<tr>
<td> ${}_0^1\text{e}$ </td>
<td> $5.49 \times 10^{-4}$ </td>
</tr>
</table>
Fig. 12.1
(a) Complete the nuclear reaction shown above. [1]
(b) (i) Show tha