科目：物理 Physics (9702)
年份：2025 夏季
试卷：Paper 44
总页数：20
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, 25: Astronomy and cosmology
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1 (a) Define gravitational field.
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(b) The gravitational field strength $g$ at a distance $x$ from the centre of a uniform spherical planet of mass $M$ is given by the expression
$$
g = \frac{GM}{x^2}
$$
where $G$ is the gravitational constant and distance $x$ is greater than the radius of the planet.
(i) Describe the pattern of the field lines outside the planet that represent the gravitational field due to the planet.
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(ii) Explain why, for small changes in vertical height near the surface of the planet, *0000800000005* DFD 5 (ii) Calculate the gravitational potential at the Earth’s surface. Give a unit with your answer. gravitational potential = ………………………………………… unit …………… [2] (d) Explain why the gravitational potential energy of two point masses is always negative. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… 2 © UCLES 2025 9702/44/M/J/25 [Turn over] DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN
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2 (a) State what is meant by two objects being in thermal equilibrium.
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(b) A mass $X$ of ice at $0^\circ \text{C}$ is placed in a beaker containing a mass $M$ of water at Celsius temperature $t$ . The beaker is perfectly insulated and has negligible heat capacity. After some time, the ice that was added reaches thermal equilibrium with the original water in the beaker.
The specif*0000800000007*
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3 (a) State what is meant by an ideal gas.
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(b) An ideal gas at a pressure of $1.6 \times 10^5$ Pa has a density of $1.9 \, \text{kg} \, \text{m}^{-3}$ .
(i) Show that the root-mean-square (r.m.s.) speed of molecules of this gas is approximately $500 \, \text{m} \, \text{s}^{-1}$ .
[3]
(ii) One molecule of the gas has a mass of $4.7 \times 10^{-26} \, \text{kg}$ .
Determine the*0000800000008* DFD 8 4 (a) State what is meant by simple harmonic motion. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (b) A small sphere is suspended from a fixed point P by a string of negligible mass, as shown in Fig. 4.1.  Fig. 4.1 The sphere is given a small horizontal displacement and is then released. The variation with time of the horizontal velocity $v$ of the sphere is shown in Fig. 4.2. 
*0000800000009* DFD 9 (i) State two times at which the sphere is passing in the same direction through the equilibrium position. time ………………… and time ………………… [1] (ii) The time interval between $t_1$ and $t_6$ is 2.2 s. Calculate the frequency of oscillation of the sphere. frequency = ………………………………… Hz [2] (c) The sphere in (b) is undergoing simple harmonic motion. Use your answer in (b)(ii) and data from Fig. 4.2 to determine the maximum displacement of the sphere from its equilibrium position. maximum displacement = ………………………………… m 3 © UCLES 2025 9702/44/M/J/25 [Turn over] DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN
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5 (a) Define electric potential at a point.
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(b) An isolated solid metal sphere of radius $r$ is given a positive charge.
The potential at the surface of the sphere is $9.0 \times 10^4 \, \text{V}$ . At a distance of $3r$ from the centre of the sphere, the electric field strength is $2.0 \times 10^5 \, \text{N} \, \text{C}^{-1}$ .
(i) Determine the electric field strength at the*0000800000011* DFD 11 (iv) Use your answer in (b)(iii) to determine the capacitance of the sphere. capacitance = ................................................... F 2 © UCLES 2025 9702/44/M/J/25 [Turn over] DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN
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6 A rectangular coil PQRS of wire is free to rotate about its axis XY, as shown in Fig. 6.1.
Fig. 6.1 (not to scale)
The coil has length QR of 5.4 cm, width PQ of 2.5 cm and has 190 turns of wire.
The plane of the coil is at an angle $\theta$ to a uniform magnetic field of flux density $5.2 \times 10^{-3}$ T.
The axis XY of the coil is normal to the field.
The current in the coil is 1.2 A.
(a) (i) Calculate the magnitude of the force on side QR of the coil.
force = ………………………………………… N [3]
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(ii) Use your answer in (a)(i) to show that the torque $\tau$ on the coil is given by
$$
\tau = 1.6 \times 10^{-3} \cos \theta \, \text{N m}.
$$
[2]
(iii) Using the expression in (a)(ii) sketch, on the axes of Fig. 6.2, a graph to show the variation of the torque $\tau$ with angle $\theta$ for values of $\theta$ between $0$ and $360^\circ$ . Label the $\tau$ axis with an appropriate scale.
$\tau / 10^{-3} \, \text{N m}$
$\theta / ^\circ$
Fig. 6.2
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(b) The coil is now replaced by an identical coil wound on a ferrous core.
Suggest, with a reason, how the torque on this coil compares with the torque on the original coil.
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......*0000800000014* DFD 14 7 A bar magnet is suspended from a spring. One pole of the magnet oscillates freely in a coil of wire, as shown in Fig. 7.1.  Fig. 7.1 The switch S is initially open. (a) The switch S is now closed. As a result, the oscillations of the magnet are lightly damped. (i) State what is meant by damping. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) Describe what is observed to indicate that the dampi
*0000800000015* DFD 15 (b) The procedure in (a) is repeated after replacing the resistor with one of greater resistance. Suggest, with a reason, the effect of this change on the oscillations. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... 2 © UCLES 2025 9702/44/M/J/25 [Turn over] DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGI
*0000800000016* DFD 16 8 An incomplete circuit diagram of a bridge rectifier is shown in Fig. 8.1.  Fig. 8.1 (a) Complete Fig. 8.1 for the bridge rectifier such that the point A is at a positive potential with respect to point B. [2] (b) The variation with time $t$ of the potential difference (p.d.) $V$ across the load resistor is shown in Fig. 8.2.  Fig. 8.2 A capacitor is now connected between points C and D of the bridge rectifier. This results in smoothing of the p.d. across the load resistor. The difference between the maximum and minimum values of the smoothed p.d. is 33% of the peak p.d. $V_0$. (i) On Fig. 8.2, draw a line to show the variation of the potential difference $V$ across the load resistor with time $t$. Your line shoul
*0000800000017* DFD 17 (ii) Use your line in (b)(i) to determine, in terms of $T$, the time constant of the smoothing circuit. time constant = ………………………………………… $T$ [3] (iii) The resistance of the load resistor is now increased. The capacitance of the capacitor is unchanged. State and explain the effect of this change on the smoothed output p.d. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ……………………………………………………………………………………………………… 2 © UCLES 2025 9702/44/M/J/25 [Turn over] DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN
*0000800000018* DFD 18 9 (a) (i) Describe what is meant by wave–particle duality. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) State the relationship between the de Broglie wavelength $\lambda$ of a particle and its momentum $p$ . State the meaning of any other symbols that you use. ............................................................................................................................... ...............................
*0000800000019* DFD 19 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Fig. 9.2 (not to scale) (i) Explain why the pattern in Fig. 9.2 provides experimental evidence to indicate a wave nature for the electrons. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [2] (ii) The speed of the electrons is increased. Suggest, with a reas
*0000800000020* DFD 20 --- **10 (a)** Describe how the piezoelectric crystal in a transducer generates ultrasound waves for use in medical diagnosis. ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... ............................................................................................................................... [3] **(b)** A parallel ultrasound beam is incident on the boundary between two media, as illustrated in Fig. 10.1. <div style="d
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(c) A parallel ultrasound beam of intensity $I_0$ enters a region of soft tissue. After passing a distance of 2.1 cm through this tissue, the intensity of the ultrasound is $0.62 I_0$ .
Calculate the linear attenuation coefficient $\mu$ of ultrasound in the soft tissue. Give a unit with your answer.
$\mu = \underline{\hspace{3cm}} \text{ unit } \underline{\hspace{3cm}} [2]$
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11 The deuterium nucleus ( $^{2}_{1}\text{H}$ ) has a mass defect of 0.002388 u. The helium-4 nucleus ( $^{4}_{2}\text{He}$ ) has a mass defect of 0.030377 u. Helium-4 is formed from deuterium in a nuclear reaction that can be represented by the equation
$$
3\,^{2}_{1}\text{H} \longrightarrow ^{4}_{2}\text{He} + ^{1}_{1}\text{p} + ^{1}_{0}\text{n}.
$$
(a) (i) State the name of this type of nuclear reaction.
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(ii) Show that the energy released when one nucleus of helium-4 is formed from deuterium is $3.47 \times 10^{-12}$ J.
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(b) A star has a radius of $6.96 \times 10^{8}$ m. Helium-4 is produced in this star, from deuterium, at a mass rat