科目：物理 Physics (9702)
年份：2019 冬季
试卷：Paper 41
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
4 Answer all the questions in the spaces provided. 1 (a) State Newton’s law of gravitation. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) A geostationary satellite orbits the Earth. The orbit of the satellite is circular and the period of the orbit is 24 hours. (i) State two other features of this orbit. 1. ............................................................................................................................... ........
5
2 (a) The kinetic theory of gases is based on a number of assumptions about the molecules of a gas.
State the assumption that is related to the volume of the molecules of the gas.
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(b) An ideal gas occupies a volume of $2.40 \times 10^{-2} \, \text{m}^3$ at a pressure of $4.60 \times 10^5 \, \text{Pa}$ and a temperature of $23^\circ \text{C}$ .
(i) Calculate the number of molecules in the gas.
number6 BLANK PAGE © UCLES 2019 9702/41/O/N/19
7 3 (a) State what is meant by *specific latent heat*. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) A student determines the specific latent heat of vaporisation of a liquid using the apparatus illustrated in Fig. 3.1.  Fig. 3.1 The heater is switched on. When the liquid is boiling at a constant rate, the balance reading is noted at 2.0 minute intervals. After 10 minutes, the current in the heater is reduced and the bal
8
The readings of the ammeter and of the voltmeter are given in Fig. 3.2.
<table>
<tr>
<th></th>
<th>ammeter reading /A</th>
<th>voltmeter reading /V</th>
</tr>
<tr>
<td>from time 0 to time 10 minutes</td>
<td>1.2</td>
<td>230</td>
</tr>
<tr>
<td>after time 10 minutes</td>
<td>1.0</td>
<td>190</td>
</tr>
</table>
Fig. 3.2
The variation with time of the balance reading is shown in Fig. 3.3.
<!-- Image: Fig. 3.3 -->
Fig. 3.3
© UCLES 2019
9702/41/O/N/199
(i) From time 0 to time 10.0 minutes, the mass of liquid evaporated is 56g.
Use Fig. 3.3 to determine the mass of liquid evaporated from time 12.0 minutes to time 22.0 minutes.
$$
\text{mass} = \underline{\hspace{5cm}} \text{g [1]}
$$
(ii) Explain why, although the power of the heater is changed, the rate of loss of thermal energy to the surroundings may be assumed to be constant.
$\underline{\hspace{10cm}}$
$\underline{\hspace{10cm}}$ [1]
(iii) Determine a value for the specific latent heat of vaporisation $L$ of the liquid.
$$
L = \underline{\hspace{5cm}} \text{Jg}^{-1} \text{[4]}
$$
(iv) Calculate the rate at which thermal energy is transferred to the surroundings.
$$
\text{rate} = \underline{\hspace{5cm}} \text{W [2]}
$$
[Total: 10]
© UCLES 2019 9702/41/O/N/19 [Turn over10 4 A mass is suspended vertically from a fixed point by means of a spring, as illustrated in Fig. 4.1. Fig. 4.1 The mass is oscillating vertically. The variation with displacement $x$ of the acceleration $a$ of the mass is shown in Fig. 4.2. Fig. 4.2 (a) (i) State what is meant by the *displacement* of the mass on the spring. ............................................................................................................................... ............................................................................................................................... [1] © UCLES 2019 9702/41/O/N/19
11
(ii) Suggest how Fig. 4.2 shows that the mass is not performing simple harmonic motion.
........................................................................................................................... [1]
(b) (i) The amplitude of oscillation of the mass may be changed.
State the maximum amplitude $x_0$ for which the oscillations are simple harmonic.
$$
x_0 = \text{................................................ cm} \quad [1]
$$
(ii) For the simple harmonic oscillations of the mass, use Fig. 4.2 to determine the frequency of the oscillations.
frequency = ................................................ Hz [3]
(c) The maximum speed of the mass when oscillating with simple harmonic motion of amplitude $x_0$ is $v_0$ .
On Fig. 4.3, show the variation with displacement $12 5 (a) A section of a coaxial cable is shown in Fig. 5.1.  Fig. 5.1 (i) Suggest two functions of the copper braid. 1. ............................................................................................................... ............................................................................................................ 2. ............................................................................................................... ............................................................................................................... [2] (ii) Suggest one application of a coaxial cable for the transmission of electrical signals. ........................................................................................................
13
(ii) The input power of the signal to the transmission cable is $2.6\,\text{W}$ . The attenuation per unit length of the cable is $6.3\,\text{dB}\,\text{km}^{-1}$ .
Use your answer in (i) to determine the maximum uninterrupted length $L$ of cable along which the signal may be transmitted.
$$
L = \underline{\hspace{5cm}}\,\text{km [2]}
$$
[Total: 7]
© UCLES 2019 9702/41/O/N/19 [Turn over14 6 (a) State an expression for the electric field strength $E$ at a distance $r$ from a point charge $Q$ in a vacuum. State the name of any other symbol used. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Two point charges A and B are situated a distance 10.0 cm apart in a vacuum, as illustrated in Fig. 6.1. charge A P x 10.0 cm charge B Fig. 6.1 A point P lies on the line joining the charges A and B. Point P is a distance $x$ from A.
15 State and explain whether the charges A and B: (i) have the same, or opposite, signs ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) have the same, or different, magnitudes. ............................................................................................................................... ............................................................................................................................... .............
16
7 (a) An ideal operational amplifier (op-amp) has infinite bandwidth and zero output impedance.
State what is meant by:
(i) *infinite bandwidth*
............................................................................................................................ [1]
(ii) *zero output impedance.*
............................................................................................................................ [1]
(b) The circuit for a non-inverting amplifier incorporating an ideal op-amp is shown in Fig. 7.1.
Fig. 7.1
The light-emitting diode (LED) emits light when the potential difference across it is at least 2.0 V.
The current in the LED must not be greater than 20 mA.
(i) Calculate the gain of the amplifier circuit.
$$
\text{gain} = \quad \text{..........17
(ii) Determine the value of $V_{IN}$ for which the value of $V_{OUT}$ is +2.0 V.
$$
V_{IN} = \underline{\hspace{5cm}} \text{ V [1]}
$$
(iii) State the maximum value of the output potential $V_{OUT}$ .
maximum potential = $\underline{\hspace{5cm}}$ V [1]
(iv) When the op-amp is saturated, the potential difference across the LED is 2.2 V.
Calculate the minimum resistance of resistor R so that the current in the LED is limited to 20 mA.
$$
\text{resistance} = \underline{\hspace{5cm}} \Omega \text{ [2]}
$$
[Total: 8]
© UCLES 2019 9702/41/O/N/19 [Turn over18
8 (a) A long straight vertical wire carries a current $I$ . The wire passes through a horizontal card EFGH, as shown in Fig. 8.1 and Fig. 8.2.
<div style="display: flex; justify-content: space-between;">
<div style="text-align: center;">
<br>
Fig. 8.1
</div>
<div style="text-align: center;">
<br>
Fig. 8.2 (view from above)
</div>
</div>
On Fig. 8.2, draw the pattern of the magnetic field produced by the current-carrying wire on the plane EFGH. [3]
(b) Two long straight parallel wires P and Q are situated a distance 3.1 cm apart, as illustrated in Fig. 8.3.
<div style="text-align: center;">
<br>
Fig. 8.3
</div>
The current in wire P is 6.2 A. The current in wire Q is 8.5 A.
The19
Calculate:
(i) the magnetic flux density at wire Q due to the current in wire P
$$
\text{flux density} = \underline{\hspace{5cm}} \text{T [2]}
$$
(ii) the force per unit length, in N m⁻¹, acting on wire Q due to the current in wire P.
$$
\text{force per unit length} = \underline{\hspace{5cm}} \text{N m}^{-1} \text{[2]}
$$
(c) The currents in wires P and Q are different in magnitude.
State and explain whether the forces per unit length on the two wires will be different.
$\underline{\hspace{10cm}}$
$\underline{\hspace{10cm}}$
$\underline{\hspace{10cm}}$ [2]
[Total: 9]
© UCLES 2019
9702/41/O/N/19
[Turn over20 BLANK PAGE © UCLES 2019 9702/41/O/N/19
21 9 Diagnosis using nuclear magnetic resonance imaging (NMRI) requires the use of a non-uniform magnetic field superimposed on a constant magnetic field of large magnitude. Explain the purpose of: (a) the large constant magnetic field ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) the non-uniform magnetic field. ...
22
10 A bridge rectifier using four ideal diodes is shown in Fig. 10.1.
Fig. 10.1
The sinusoidal alternating electromotive force (e.m.f.) applied between points A and B has a root-mean-square (r.m.s.) value of 7.0 V.
(a) (i) On Fig. 10.1, circle the diodes that conduct when point B is positive with respect to point A. [1]
(ii) Calculate the maximum potential difference $V_{MAX}$ across resistor R.
$$
V_{MAX} = \text{................................................... V [1]}
$$
© UCLES 2019 9702/41/O/N/1923 (b) A capacitor is connected into the circuit to produce smoothing of the potential difference across resistor R. The variation with time $t$ of the potential difference $V$ across resistor R is shown in Fig. 10.2.  Fig. 10.2 (i) On Fig. 10.1, draw the symbol for a capacitor, connected so as to produce smoothing. [1] (ii) State the effect, if any, on the magnitude of the ripple on $V$ when, separately: 1. a capacitor of larger capacitance is used ............................................................................................................................... 2. the resistor R has a smaller resistance. ............................................................................................................................... 2 © UCLES 2019
24
11 (a) With reference to the photoelectric effect, state what is meant by work function energy.
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(b) The work function energy of a clean metal surface is $5.5 \times 10^{-19}$ J.
Electromagnetic radiation of wavelength 280 nm is incident on the metal surface. The metal is in a vacuum.
(i) Calculate:
1. the photon energy
photon energy = ................................................... J [2]
2. t25
(c) The electromagnetic radiation incident on the metal surface may change in intensity or in frequency.
Complete Fig. 11.1 by inserting either ‘increases’ or ‘decreases’ or ‘no change’ to describe the effects of the changes shown on the maximum speed and on the rate of emission of electrons.
<table>
<tr>
<th>change</th>
<th>maximum speed of electrons</th>
<th>rate of emission of electrons</th>
</tr>
<tr>
<td>reduced intensity at constant frequency</td>
<td>........................................</td>
<td>........................................</td>
</tr>
<tr>
<td>increased frequency at constant intensity</td>
<td>........................................</td>
<td>........................................</td>
</tr>
</table>
Fig. 11.1
26
12 One possible nuclear reaction that takes place is
$$
{}^{235}_{92}\text{U} + {}^1_0\text{n} \rightarrow {}^{95}_{42}\text{Mo} + {}^{139}_{57}\text{La} + 2{}_0^1\text{n} + 7{}_1^0\text{e}
$$
Data for nuclei in this reaction are given in Fig. 12.1.
<table>
<tr>
<th>nucleus</th>
<th>mass/u</th>
<th>total mass of separate nucleons/u</th>
<th>mass defect/u</th>
<th>binding energy per nucleon/MeV</th>
</tr>
<tr>
<td>${}^{95}_{42}\text{Mo}$</td>
<td>94.906</td>
<td>95.765</td>
<td>0.859</td>
<td>8.443</td>
</tr>
<tr>
<td>${}^{139}_{57}\text{La}$</td>
<td>138.906</td>
<td>140.125</td>
<td>1.219</td>
<td>8.189</td>
</tr>
<tr>
<td>${}^{235}_{92}\text{U}$</td>
<td>235.044</td>
<td>236.909</td>
<td>1.8627
(c) Calculate the total energy, in MeV, released in this nuclear reaction.
energy = ………………………………………… MeV [2]
(d) The nuclei in $1.2 \times 10^{-7}$ mol of uranium-235 all undergo this reaction in a time of 25 ms.
Calculate the average power release during the time of 25 ms.
power = ………………………………………… W 3
© UCLES 2019 9702/41/O/N/19