科目：物理 Physics (9702)
年份：2012 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, 20: Magnetic fields, 21: Alternating currents, 22: Quantum physics, 23: Nuclear physics, 24: Medical physics
4 Section A Answer all the questions in the spaces provided. For Examiner's Use 1 (a) State Newton’s law of gravitation. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) The Earth and the Moon may be considered to be isolated in space with their masses concentrated at their centres. The orbit of the Moon around the Earth is circular with a radius of $3.84 \times 10^5$ km. The period of the orbit is 27.3 days. Show that (i) the angular speed
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(c) The mass of the Moon is $7.4 \times 10^{22} \, \text{kg}$ .
(i) Using data from (b), determine the gravitational force between the Earth and the Moon.
force = ………………………………………… N [2]
(ii) Tidal action on the Earth’s surface causes the radius of the orbit of the Moon to increase by 4.0 cm each year.
Use your answer in (i) to determine the change, in one year, of the gravitational potential energy of the Moon. Explain your working.
energy change = ………………………………………… J [3]
For Examiner’s Use
© UCLES 2012 9702/42/M/J/12 [Turn over
Note: The vertical text "For Examiner’s Use" is preserved as a side note in the Markdown structure. The mathematical expressions are rendered in LaTeX notation as requested. The footer information is preserved exactly as it appears.6 2 A ball of mass 37 g is held between two fixed points A and B by two stretched helical springs, as shown in Fig. 2.1. <div style="text-align: center;">  <br /> Fig. 2.1 </div> The ball oscillates along the line AB with simple harmonic motion of frequency 3.5 Hz and amplitude 2.8 cm. (a) Show that the total energy of the oscillations is 7.0 mJ. [2] (b) At two points in the oscillation of the ball, its kinetic energy is equal to the potential energy stored in the springs. Calculate the magnitude of the displacement at which this occurs. displacement = ______________________ cm [3] © UCLES 2012 9702/42/M/J/12 For Examiner’s Use
7 (c) On the axes of Fig. 2.2 and using your answers in (a) and (b), sketch a graph to show the variation with displacement $x$ of (i) the total energy of the system (label this line T), [1] (ii) the kinetic energy of the ball (label this line K), [2] (iii) the potential energy stored in the springs (label this line P). [2] <div style="text-align: center;">  <br/> Fig. 2.2 </div> (d) The arrangement in Fig. 2.1 is now rotated through $90^\circ$ so that the line AB is vertical and the ball oscillates in a vertical plane. Suggest one form of energy, other than those in (c), that must be taken into consideration when plotting new graphs to show energy changes with displacement. .................................................................................
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9 3 (a) State what is meant by the *internal energy* of a system. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) State and explain qualitatively the change, if any, in the internal energy of the following systems: (i) a lump of ice at 0°C melts to form liquid water at 0°C, ............................................................................................................................... .............................................
10 4 A charged point mass is situated in a vacuum. A proton travels directly towards the mass, as illustrated in Fig. 4.1. <div style="text-align: center;">  </div> Fig. 4.1 When the separation of the mass and the proton is $r$, the electric potential energy of the system is $U_p$. The variation with $r$ of the potential energy $U_p$ is shown in Fig. 4.2. <div style="text-align: center;">  </div> Fig. 4.2 © UCLES 2012 9702/42/M/J/12 For Examiner's Use Note: The images referenced in the markdown are placeholders since actual image data cannot be extracted or rendered here. In a real implementation, these would be replaced with the actual image files or URLs.
11 (a) (i) Use Fig. 4.2 to state and explain whether the mass is charged positively or negatively. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) The gradient at a point on the graph of Fig. 4.2 is $G$ . Show that the electric field strength $E$ at this point due to the charged point mass is given by the expression $$ Eq = G $$ where $q$ is the charge at this point. ...........................................................................
12 5 (a) Define the *tesla*. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [3] (b) A horseshoe magnet is placed on a balance. A stiff metal wire is clamped horizontally between the poles, as illustrated in Fig. 5.1.  Fig. 5.1 The magnetic flux density in the space between the poles of the magnet is unif
13 (ii) Calculate the magnitude of the magnetic flux density between the poles of the magnet. For Examiner's Use flux density = ………………………………………… T [2] (c) A low frequency alternating current is now passed through the wire in (b). The root-mean-square (r.m.s.) value of the current is 5.6 A. Describe quantitatively the variation of the reading seen on the balance. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2] © UCLES 2012 9702/42/M/J/12 [Turn over
14 6 (a) Describe the main principles of the determination of the charge on an oil drop by Millikan’s experiment. You may draw a diagram if you wish. For Examiner’s Use ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ................................................................................................................
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7 The photoelectric effect may be represented by the equation
$$
\text{photon energy} = \text{work function energy} + \text{maximum kinetic energy of electron}.
$$
(a) State what is meant by *work function energy*.
...............................................................................................................................
............................................................................................................................... [1]
(b) The variation with frequency $f$ of the maximum kinetic energy $E_K$ of photoelectrons emitted from the surface of sodium metal is shown in Fig. 7.1.
Fig. 7.1
Use the gradient of the graph of Fig. 7.1 to determine a value for the Planck constant $h$ . Show your working.
$h = \underline16 (c) The sodium metal in (b) has a work function energy of 2.4 eV. The sodium is replaced by calcium which has a work function energy of 2.9 eV. On Fig. 7.1, draw a line to show the variation with frequency $f$ of the maximum kinetic energy $E_K$ of photoelectrons emitted from the surface of calcium. [3] For Examiner’s Use © UCLES 2012 9702/42/M/J/12
17 8 The element strontium has at least 16 isotopes. One of these isotopes is strontium-89. This isotope has a half-life of 52 days. (a) State what is meant by isotopes. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) Calculate the probability per second of decay of a nucleus of strontium-89. probability = ........................................ s⁻¹ [3] (c) A laboratory prepares a strontium-89 source. The activity of this source is measured
18 Section B Answer all the questions in the spaces provided. For Examiner's Use 9 An operational amplifier (op-amp) may be used as part of the processing unit in an electronic sensor. (a) State four properties of an ideal operational amplifier. 1. ............................................................................................................... 2. ............................................................................................................... 3. ............................................................................................................... 4. ............................................................................................................... [4] (b) A comparator circuit incorporating an ideal op-amp is shown in Fig. 9.1. F
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(c) The output potential $V_{OUT}$ is to be displayed using two light-emitting diodes (LEDs). A diode emitting red light is to indicate when $V_{OUT}$ is positive and a diode emitting green light is to be used to indicate when $V_{OUT}$ is negative.
Complete Fig. 9.3 to show the connections of the two LEDs to the output of the op-amp. Label each LED with the colour of light that it emits.
<div style="text-align: center;">
<br/>
Fig. 9.3
</div>
[3]
For Examiner's Use
© UCLES 2012 9702/42/M/J/12 [Turn over
Note: The image placeholder is used since the actual image cannot be rendered in Markdown. In practice, you would replace `image_placeholder` with the actual image file path or URL.20 10 (a) An aluminium block is placed near to a small source of X-ray radiation, as shown in Fig. 10.1. <div style="text-align: center;">  </div> Fig. 10.1 X-rays from the source are detected at point A and at point B. State two reasons why the intensity of the X-ray beam at point B is not as great as the intensity at point A. 1. ............................................................................................................................... 2. ............................................................................................................................... [2] (b) A cross-section through a model of a finger is shown in Fig. 10.2. <div style="text-align: center;">  </div> Fig. 10.2 The thickness of the mo
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Data for the linear attenuation (absorption) coefficient $\mu$ for the bone and the soft tissue in the model are given in Fig. 10.3.
<table>
<tr>
<td></td>
<td> $\mu / \text{cm}^{-1}$ </td>
</tr>
<tr>
<td>bone</td>
<td>3.0</td>
</tr>
<tr>
<td>soft tissue</td>
<td>0.27</td>
</tr>
</table>
Fig. 10.3
Calculate the ratio
$$
\frac{\text{intensity of X-ray beam incident on the model}}{\text{intensity of X-ray beam emergent from the model}}
$$
for
(i) the beam AB,
ratio = ………………………………………… [2]
(ii) the beam CD.
ratio = ………………………………………… [2]
(c) Use your answers in (b) to suggest why, for this model, an X-ray image with good contrast may be obtained.
……………………………………………………………………………………………………… [1]
© UCLES 2012 9702/42/M/J/12 [Turn over
For Examiner’s 22 11 A signal that is transmitted over a long distance will be attenuated and it will pick up noise. (a) State what is meant by (i) attenuation, ........................................................................................................................... [1] (ii) noise. ........................................................................................................................... [2] (b) Explain why regenerator amplifiers do not amplify the noise that has been picked up on digital signals. ........................................................................................................................... [2] (c) A transmitter on Earth produces a signal of power 2.4 kW. This signal, when received by a satellite, is attenuated by 195 dB. Calculate
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12 An incomplete simplified block diagram of the circuitry for a mobile-phone handset is shown in Fig. 12.1.
For Examiner's Use
plaintext
aerial
|
switch
/ \
amplifier tuning circuit
| |
X demodulator
| |
oscillator Y
| |
parallel- to-serial converter DAC
| |
ADC amplifier
| |
amplifier loudspeaker
|
microphone
```
Fig. 12.1
(a) State the name of the block labelled
(i) X,
...........................................................................................................[1]
(ii) Y.
.....................................................