科目：物理 Physics (9702)
年份：2010 夏季
试卷：Paper 43
总页数：16
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, 23: Nuclear physics, 24: Medical physics
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Section A
Answer all the questions in the spaces provided.
For Examiner's Use
1 (a) Define gravitational potential at a point.
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(b) The Earth may be considered to be an isolated sphere of radius $R$ with its mass concentrated at its centre. The variation of the gravitational potential $\phi$ with distance $x$ from the centre of the Earth is shown in Fig. 1.1.
<div style="text-align: center;">
![5 (ii) A meteorite is at rest at infinity. The meteorite travels from infinity towards the Earth. Calculate the speed of the meteorite when it is at a distance of $2R$ above the Earth’s surface. Explain your working. speed = ……………………………… ms⁻¹ [4] (iii) In practice, the Earth is not an isolated sphere because it is orbited by the Moon, as illustrated in Fig. 1.2. initial path of meteorite Earth Moon Fig. 1.2 (not to scale) The initial path of the meteorite is also shown. Suggest two changes to the motion of the meteorite caused by the Moon. 1. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… 2. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… [2] © UCLES 2010 9702/43/M/J/10 [Turn over For Examiner’s
6 2 A long strip of springy steel is clamped at one end so that the strip is vertical. A mass of 65 g is attached to the free end of the strip, as shown in Fig. 2.1. <div style="text-align: center;">  <br/> Fig. 2.1 </div> The mass is pulled to one side and then released. The variation with time $t$ of the horizontal displacement of the mass is shown in Fig. 2.2. <div style="text-align: center;">  <br/> Fig. 2.2 </div> The mass undergoes damped simple harmonic motion. (a) (i) Explain what is meant by damping. ............................................................................................................................... ...............................................................................................
7 (ii) Suggest, with a reason, whether the damping is light, critical or heavy. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) (i) Use Fig. 2.2 to determine the frequency of vibration of the mass. frequency = ........................................ Hz [1] (ii) Hence show that the initial energy stored in the steel strip before the mass is released is approximately 3.2 mJ. [2] (c) After eight complete oscillations of the mass, the amplitude o
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3 (a) The resistance of a thermistor at $0^\circ \text{C}$ is $3840\ \Omega$ . At $100^\circ \text{C}$ the resistance is $190\ \Omega$ . When the thermistor is placed in water at a particular constant temperature, its resistance is $2300\ \Omega$ .
(i) Assuming that the resistance of the thermistor varies linearly with temperature, calculate the temperature of the water.
temperature = ……………………………… °C [2]
(ii) The temperature of the water, as measured on the thermodynamic scale of temperature, is $286\ \text{K}$ .
By reference to what is meant by the thermodynamic scale of temperature, comment on your answer in (i).
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4 Two point charges A and B each have a charge of $+6.4 \times 10^{-19} \, \text{C}$ . They are separated in a vacuum by a distance of $12.0 \, \mu\text{m}$ , as shown in Fig. 4.1.
<div style="text-align: center;">
</div>
Fig. 4.1
Points P and Q are situated on the line AB. Point P is $3.0 \, \mu\text{m}$ from charge A and point Q is $3.0 \, \mu\text{m}$ from charge B.
(a) Calculate the force of repulsion between the charges A and B.
force = _________________________ N [3]
(b) Explain why, without any calculation, when a small test charge is moved from point P to point Q, the net work done is zero.
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5 (a) State two functions of capacitors in electrical circuits.
1. .......................................................................................................................
2. .......................................................................................................................
[2]
(b) Three capacitors, each marked ‘30 $\mu$ F, 6V max’, are arranged as shown in Fig. 5.1.
Fig. 5.1
Determine, for the arrangement shown in Fig. 5.1,
(i) the total capacitance,
$$
\text{capacitance} = \underline{\hspace{3cm}} \, \mu\text{F} \, [2]
$$
(ii) the maximum potential difference that can safely be applied between points A and B.
$$
\text{potential difference} = \underline{\hspace{3cm}} \, \text{V} \, [2]
$$
© UCLES 2010
9702/43/M/J/10
For Examiner’s Use
N11
(c) A capacitor of capacitance $4700\,\mu\text{F}$ is charged to a potential difference of $18\,\text{V}$ . It is then partially discharged through a resistor. The potential difference is reduced to $12\,\text{V}$ . Calculate the energy dissipated in the resistor during the discharge.
energy = ……………………………… J [3]
For Examiner’s Use
© UCLES 2010 9702/43/M/J/10 [Turn over
Note: The vertical line on the right side of the page is not represented in Markdown as it is a layout element and not textual content. The "For Examiner’s Use" label is placed to the right of the main text block as per the image. The footer information is placed at the bottom as shown.12 6 (a) A uniform magnetic field has constant flux density $B$ . A straight wire of fixed length carries a current $I$ at an angle $\theta$ to the magnetic field, as shown in Fig. 6.1. <div style="text-align: center;">  <br/> Fig. 6.1 </div> (i) The current $I$ in the wire is changed, keeping the angle $\theta$ constant. On Fig. 6.2, sketch a graph to show the variation with current $I$ of the force $F$ on the wire. <div style="text-align: center;">  <br/> Fig. 6.2 </div> [2] © UCLES 2010 9702/43/M/J/10 For Examiner’s Use
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(ii) The angle $\theta$ between the wire and the magnetic field is now varied. The current $I$ is kept constant.
On Fig. 6.3, sketch a graph to show the variation with angle $\theta$ of the force $F$ on the wire.
$\begin{array}{c}
F \\
\uparrow \\
0 \quad 30 \quad 60 \quad 90 \\
\theta /^\circ
\end{array}$
Fig. 6.3
[3]
(b) A uniform magnetic field is directed at right-angles to the rectangular surface PQRS of a slice of a conducting material, as shown in Fig. 6.4.
$\begin{array}{c}
\text{uniform magnetic field} \\
\downarrow \\
\text{Q} \quad \text{R} \\
\text{P} \quad \text{S} \\
\text{direction of movement of electrons}
\end{array}$
Fig. 6.4
Electrons, moving towards the side SR, enter the slice of conducting material. The electrons enter the slice at right-angles to side SR14 7 (a) Explain what is meant by the root-mean-square (r.m.s.) value of an alternating voltage. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) An alternating voltage $V$ is represented by the equation $$ V = 220 \sin(120\pi t), $$ where $V$ is measured in volts and $t$ is in seconds. For this alternating voltage, determine (i) the peak voltage, peak voltage = ........................................ V [1] (ii) the r.m.s. voltage, r.m.s. v
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8 Americium-241 is an artificially produced radioactive element that emits $\alpha$ -particles.
A sample of americium-241 of mass $5.1\,\mu\text{g}$ is found to have an activity of $5.9 \times 10^5\,\text{Bq}$ .
(a) Determine, for this sample of americium-241,
(i) the number of nuclei,
number = ………………………………………… [2]
(ii) the decay constant,
decay constant = ………………………………………… s $^{-1}$ [2]
(iii) the half-life, in years.
half-life = ………………………………………… years [2]
(b) Another radioactive element has a half-life of approximately 4 hours.
Suggest why measurement of the mass and activity of a sample of this element is not appropriate for the determination of its half-life.
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© UCLES 2010 9702/43/M/J/10 [Turn over
For Examiner’s Use
Note: Th16 Section B Answer all the questions in the spaces provided. For Examiner's Use 9 (a) Negative feedback may be used in amplifier circuits. State (i) what is meant by negative feedback, ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) two effects of negative feedback on an amplifier incorporating an operational amplifier (op-amp). 1. ..............................................................................................................
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(ii) the resistance of the resistor R.
resistance = ………………………………………… $\Omega$ [2]
(c) The maximum potential produced by the microphone at point P on Fig. 9.1 is 95 mV.
The power supply for the operational amplifier may be either $+/- 5 \text{ V}$ or $+/- 9 \text{ V}$ .
State which power supply should be used. Justify your answer quantitatively.
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For Examiner’s Use
© UCLES 2010 9702/43/M/J/10 [Turn over18 10 (a) State the name of an electrical sensing device that will respond to changes in (i) length, ................................................................................................................... [1] (ii) pressure. ................................................................................................................... [1] (b) A relay is sometimes used as the output of a sensing circuit. The output of a particular sensing circuit is either $+2V$ or $-2V$. On Fig. 10.1, draw symbols for a relay and any other necessary component so that the external circuit is switched on only when the output from the sensing circuit is $+2V$. <div style="text-align: center;">  <br/> Fig. 10.1 </div> [4] For Examiner’s Use © UCLES 2010 9
19 11 Explain the main principles behind the generation of ultrasound to obtain diagnostic information about internal body structures. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ..................