科目：物理 Physics (9702)
年份：2012 冬季
试卷：Paper 42
总页数：16
章节：12-13: Circular Motion & Gravitational Fields, 14-16: Temperature, Ideal Gases & Thermodynamics, 17: Oscillations, 19: Capacitance, 20: Magnetic fields, 22: Quantum physics, 24: Medical physics
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Section A
Answer all the questions in the spaces provided.
For Examiner's Use
1 (a) State Newton’s law of gravitation.
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(b) A satellite of mass $m$ is in a circular orbit of radius $r$ about a planet of mass $M$ . For this planet, the product $GM$ is $4.00 \times 10^{14} \, \text{N} \, \text{m}^2 \, \text{kg}^{-1}$ , where $G$ is the gravitational constant. The planet may be assumed to be isolated in5 Resistive forces cause the satellite to move into a new orbit of radius $7.30 \times 10^6$ m. Determine, for the satellite, the change in 1. kinetic energy, change in kinetic energy = ………………………………………… J [2] 2. gravitational potential energy. change in potential energy = ………………………………………… J [2] (iii) Use your answers in (ii) to explain whether the linear speed of the satellite increases, decreases or remains unchanged when the radius of the orbit decreases. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2] © UCLES 2012 9702/42/O/N/12 [Turn over For Examiner’s Use
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2 A student suggests that, when an ideal gas is heated from $100^\circ\text{C}$ to $200^\circ\text{C}$ , the internal energy of the gas is doubled.
(a) (i) State what is meant by *internal energy*.
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(ii) By reference to one of the assumptions of the kinetic theory of gases and your answer in (i), deduce what is meant by the internal energy of an ideal gas.
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3 (a) Two metal spheres are in thermal equilibrium.
State and explain what is meant by *thermal equilibrium*.
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(b) An electric water heater contains a tube through which water flows at a constant rate.
The water in the tube passes over a heating coil, as shown in Fig. 3.1.
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Fig. 3.1
The water flows into the tube at a temperature of8
4 A ball is held between two fixed points A and B by means of two stretched springs, as shown in Fig. 4.1.
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Fig. 4.1
The ball is free to oscillate horizontally along the line AB. During the oscillations, the springs remain stretched and do not exceed their limits of proportionality.
The variation of the acceleration $a$ of the ball with its displacement $x$ from its equilibrium position is shown in Fig. 4.2.
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Fig. 4.2
© UCLES 2012 9702/42/O/N/12
For Examiner's Use9 (a) State and explain the features of Fig. 4.2 that indicate that the motion of the ball is simple harmonic. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [4] (b) Use Fig. 4.2 to determine, for the oscillations of the ball, (i) the amplitude, amplitude = ........................................ cm [1] (ii) the frequency.
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5 (a) (i) Define capacitance.
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(ii) A capacitor is made of two metal plates, insulated from one another, as shown in Fig. 5.1.
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Fig. 5.1
Explain why the capacitor is said to store energy but not charge.
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...11 (i) Calculate the combined capacitance of the capacitors X, Y and Z. capacitance = ……………………………… $\mu$ F [2] (ii) Explain why, when the potential difference of 9.0V is applied, the charge on one plate of capacitor X is 72 $\mu$ C. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………… [2] (iii) Determine 1. the potential difference across capacitor X, potential difference = ……………………………… V [1] 2. the charge on one plate of capacitor Y. charge = ……………………………… $\mu$ C 2 UCLES 2012 9702/42/O/N/12 [Turn over For Examiner’s Use
12 6 (a) (i) State the condition for a charged particle to experience a force in a magnetic field. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) State an expression for the magnetic force $F$ acting on a charged particle in a magnetic field of flux density $B$. Explain any other symbols you use. ............................................................................................................................... .....................
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7 (a) State Lenz’s law.
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(b) A simple transformer with a soft-iron core is illustrated in Fig. 7.1.
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Fig. 7.1
(i) Explain why the core is
1. made of iron,
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..................................................14 8 (a) State what is meant by a photon. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) It has been observed that, where photoelectric emission of electrons takes place, there is negligible time delay between illumination of the surface and emission of an electron. State three other pieces of evidence provided by the photoelectric effect for the particulate nature of electromagnetic radiation. 1. ...............................................
15 BLANK PAGE Please turn over for Section B. © UCLES 2012 9702/42/O/N/12 [Turn over
16 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 three properties of an ideal op-amp. 1. ....................................................................................................................... 2. ....................................................................................................................... 3. ....................................................................................................................... [3] (b) A comparator circuit incorporating an ideal op-amp is shown in Fig. 9.1. Fig. 9.1 (i) In one application of the comparator, $V_2$ is kept constant at +1.5V. The variation with tim
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For Examiner's Use
Fig. 9.2
On Fig. 9.2, show the variation with time $t$ of the output potential $V_{OUT}$. [4]
(ii) Two light-emitting diodes (LEDs) R and G are connected to the output of the op-amp in Fig. 9.1 such that R emits light for a longer time than G.
On Fig. 9.1, draw the symbols for the two diodes connected to the output of the op-amp and label the diodes R and G. [3]
© UCLES 2012 9702/42/O/N/12 [Turn over18 10 Outline the principles of CT scanning. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................
19 11 (a) In modern communications systems, the majority of data is transmitted in digital form rather than analogue form. Suggest three advantages of the transmission of data in digital form. 1. ....................................................................................................................... 2. ....................................................................................................................... 3. ....................................................................................................................... [3] (b) A recording is made of some music. For this recording, the music is sampled at a rate of 44.1 kHz and each sample consists of a 16-bit word. (i) Suggest the effect on the quality of the recording of 1. sampling at a high