科目：物理 Physics (9702)
年份：2018 夏季
试卷：Paper 42
总页数：24
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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5 Answer all the questions in the spaces provided. 1 (a) (i) A gravitational field may be represented by lines of gravitational force. State what is meant by a line of gravitational force. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ [1] (ii) By reference to lines of gravitational force near to the surface of the Earth, explain why the gravitational field strength $g$ close to the Earth’s surface is approximately constant. ..............................
6
2 (a) Use one of the assumptions of the kinetic theory of gases to explain why the potential energy of the molecules of an ideal gas is zero.
...............................................................................................................................
............................................................................................................................... [1]
(b) The average translational kinetic energy $E_K$ of a molecule of an ideal gas is given by the expression
$$
E_K = \frac{1}{2} m \langle c^2 \rangle = \frac{3}{2} kT
$$
where $m$ is the mass of a molecule and $k$ is the Boltzmann constant.
State the meaning of the symbol
(i) $\langle c^2 \rangle$ ,
.....................................................................................7 2. the increase in average kinetic energy of a molecule during the heating process. increase = ………………………………………… J [1] (ii) Use your answer in (i) part 2 to determine the final temperature $T$, in kelvin, of the gas in the cylinder. $T$ = ………………………………………… K 3 © UCLES 2018 9702/42/M/J/18 [Turn over
8 3 (a) During melting, a solid becomes liquid with little or no change in volume. Use kinetic theory to explain why, during the melting process, thermal energy is required although there is no change in temperature. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [3] (b) An aluminium can of mass 160g contains a mass of 330g of
9
Assuming no exchange of thermal energy with the surroundings,
(i) show that the loss in thermal energy of the can and the warm water is $2.3 \times 10^4 \, \text{J}$ ,
[2]
(ii) use the information in (i) to calculate a value $L$ for the specific latent heat of fusion of ice.
$$
L = \underline{\hspace{5cm}} \, \text{J} \, \text{g}^{-1} \, [2]
$$
[Total: 7]
© UCLES 2018 9702/42/M/J/18 [Turn over10
4 (a) State two conditions necessary for a mass to be undergoing simple harmonic motion.
1. ...............................................................................................................................
2. ...............................................................................................................................
[2]
(b) A trolley of mass 950g is held on a horizontal surface by means of two springs attached to fixed points P and Q, as shown in Fig. 4.1.
<!-- Image: Fig. 4.1 -->
Fig. 4.1
The springs, each having a spring constant $k$ of $230 \, \text{N} \, \text{m}^{-1}$ , are always extended.
The trolley is displaced along the line of the springs and then released.
The variation with time $t$ of the displacement $x$ of the trolley is shown i11 (i) 1. State and explain whether the oscillations of the trolley are heavily damped, critically damped or lightly damped. ............................................................................................................................... ............................................................................................................................... 2. Suggest the cause of the damping. ............................................................................................................................... ............................................................................................................................... .......................................................................................................................
12 5 (a) In radio communication, the bandwidth of an FM transmission is greater than the bandwidth of an AM transmission. State (i) what is meant by *bandwidth*, ............................................................................................................................... ............................................................................................................................... [1] (ii) one advantage and one disadvantage of a greater bandwidth. advantage: ............................................................................................................................... ............................................................................................................................... disadvantage: ........................
13
(iii) the minimum time between a maximum and a minimum transmitted frequency.
$$
\text{time} = \text{................................................... s [1]}
$$
[Total: 7]
© UCLES 2018 9702/42/M/J/18 [Turn over14
6 (a) Explain what is meant by the *capacitance* of a parallel plate capacitor.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [3]
(b) Three parallel plate capacitors each have a capacitance of $6.0\,\mu\mathrm{F}$ .
Draw circuit diagrams, one in each case, to show how the capacitors may be connected together to give a comb15
(i) Calculate the combined capacitance of the capacitors.
$$
\text{capacitance} = \underline{\hspace{5cm}} \, \mu\text{F} \, [1]
$$
(ii) Use your answer in (i) to determine, for the capacitor of capacitance $3.0 \, \mu\text{F}$ ,
1. the charge on one plate of the capacitor,
$$
\text{charge} = \underline{\hspace{5cm}} \, \mu\text{C}
$$
2. the energy stored in the capacitor.
$$
\text{energy} = \underline{\hspace{5cm}} \, \text{J} \, [4]
$$
[Total: 10]
© UCLES 2018 9702/42/M/J/18 [Turn over16 7 (a) Negative feedback is often used in amplifiers. State (i) what is meant by *negative feedback*, ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) two effects of negative feedback on the gain of an amplifier. 1. ............................................................................................................................... .....................................................................................................
17
(ii) Determine the output potential difference $V_{OUT}$ for an input potential difference $V_{IN}$ of
1. $+0.60\,V$,
$$
V_{OUT} = \underline{\hspace{5cm}}\,V
$$
2. $-2.1\,V$.
$$
V_{OUT} = \underline{\hspace{5cm}}\,V
$$
[2]
(iii) The gain of the amplifier shown in Fig. 7.1 is constant.
State one change that may be made to the circuit of Fig. 7.1 so that the amplifier circuit monitors temperature with the gain decreasing as the temperature rises.
$\underline{\hspace{10cm}}$ [1]
[Total: 8]
© UCLES 2018 9702/42/M/J/18 [Turn over18 8 (a) Explain how a uniform magnetic field and a uniform electric field may be used as a velocity selector for charged particles. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ...............................................................................................................................[3] © UCLES 2018 9702/42/M/J/18
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(b) Particles having mass $m$ and charge $+1.6 \times 10^{-19} \, \text{C}$ pass through a velocity selector. They then enter a region of uniform magnetic field of magnetic flux density $94 \, \text{mT}$ with speed $3.4 \times 10^4 \, \text{m} \, \text{s}^{-1}$ , as shown in Fig. 8.1.
<div style="text-align: center;">
<br/>
Fig. 8.1
</div>
The direction of the uniform magnetic field is into the page and normal to the direction in which the particles are moving.
The particles are moving in a vacuum in a circular arc of diameter $15.0 \, \text{cm}$ .
Show that the mass of one of the particles is $20 \, \mu \text{u}$ .
[4]
(c) On Fig. 8.1, sketch the path in the uniform magnetic field of a particle of mass $22 \, \mu \text{u}$ having the same charge and s20
9 (a) State what is meant by the *magnetic flux linkage* of a coil.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [3]
(b) A coil of wire has 160 turns and diameter 2.4 cm. The coil is situated in a uniform magnetic field of flux density 7.5 mT, as shown in Fig. 9.1.
<div style="text-align: center;">
 The magnetic flux density $B$ in the coil in (b) is now varied with time $t$ as shown in Fig. 9.2.  Fig. 9.2 Use data in (b) to show, on Fig. 9.3, the variation with time $t$ of the e.m.f. $E$ induced in the coil.  Fig. 9.3 4 © UCLES 2018 9702/42/M/J/18 [Turn over
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10 (a) Describe the photoelectric effect.
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(b) Data for the work function energy $\phi$ of two metals are shown in Fig. 10.1.
<table>
<tr>
<th></th>
<th> $\phi$ / J</th>
</tr>
<tr>
<td>sodium</td>
<td> $3.8 \times 10^{-19}$ </td>
</tr>
<tr>
<td>zinc</td>
<td> $5.8 \times 10^{-19}$ </td>
</tr>
</table>
Fig. 10.1
Light of wavelength 420 nm is incident on the surface24 11 (a) Describe the basic principles of CT scanning (computed tomography). ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ...........................................................................
25 (b) By reference to your answer in (a), suggest why (i) CT scanning was not possible before fast computers with large memories were available, ............................................................................................................................... ............................................................................................................................... ...............................................................................................................................[1] (ii) the radiation dose for a CT scan is much larger than for an X-ray image of a leg bone. ............................................................................................................................... .......................................
26 12 (a) State what is meant by radioactive decay. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) An unstable nuclide P has decay constant $\lambda_P$ and decays to form a nuclide D. This nuclide D is unstable and decays with decay constant $\lambda_D$ to form a stable nuclide S. The decay chain is illustrated in Fig
27
(i) On Fig. 12.2, use the symbols P, D and S to identify the curve for each of the three nuclides. [2]
(ii) The half-life of nuclide P is 60.0 minutes.
Calculate the decay constant $\lambda_P$ in s $^{-1}$ , of this nuclide.
$$
\lambda_P = \text{................................................... s}^{-1} \text{ [2]}
$$
(c) In the decay chain shown in Fig. 12.1, $\lambda_P$ is approximately equal to $5\lambda_D$ .
The decay chain of a different nuclide E is illustrated in Fig. 12.3.
<div style="text-align: center;">
<table>
<tr>
<td>nuclide E</td>
<td>decay constant $\lambda_E$ </td>
<td>nuclide F</td>
<td>decay constant $\lambda_F$ </td>
<td>nuclide G</td>
</tr>
</table>
</div>
Fig. 12.3
The decay constant $\lambda_F$ of nuclide F is ve