43. Suppose a coil has a magnetic dipole moment and is placed in a uniform magnetic field , where I and A are the current and area of the coil, respectively. What is the torque experienced by the coil? The vectors i,j,k are unit vectors corresponding to the x, y, and z axes, respectively.
(A)
(B)
(C)
(D)
(E)

39. When a driver is traveling at a speed of v1, they hear the frequency of a distant whistle as f₁. When they reduce their speed to v2, the frequency of the whistle is heard as f2. The car is moving toward the sound source. Assuming the sound source is stationary relative to the ground, what is the speed of sound? (A)(B)(C)(D)(E)

40. A moving hydrogen atom absorbs a photon and then comes to rest. Assume that the kinetic energy of the hydrogen atom can be neglected. Find the maximum possible wavelength of this photon. The ground state energy of the hydrogen atom is -13.6 eV. [hc=1240 eV.nm] (A) 121.6 nm (B) 243.2 nm (C) 178.6 nm (D) 289.1 nm (E) 342.5 nm

41. As shown in the Figure, a partition divides the space into two sections, A and B. The molar mass of the gas in section A is 14 g, while the molar mass of the gas in section B is 32 g. Assuming the total mass of the gases in A and B is the same, what is the ratio XA/XB of their lengths when equilibrium is reached? (A) 13/5 (B) 13/2 (C) 17/4 (D) 14/3 (E) 16/7

42. A parallel-plate capacitor has plates of area A = 8 m² and separation d = 1.5 mm. A dielectric sheet of the same area and thickness is placed between the plates. The dielectric constant is ɛ = 4.2. Determine the capacitance filled with the dielectric. [vacuum permittivity is ε0 = C/N·m²] (A)F (B)F (C)F (D) F (E)F

44. Two electric dipoles are placed horizontally along the x-axis, but one of them is oriented in the opposite direction, as shown in the Figure. Both electric dipoles have the same magnitude p. What is the electric potential V at point A on the z-axis at a distance L? (A)(B) (C)(D)(E)

45. During human respiration, oxygen passes through the alveoli (肺泡) into the bloodstream. Suppose an alveolus is approximated as a sphere with a volumn V = m³ and an internal pressure P = 1.2×105 Pa. The oxygen content inside the alveolus is 25%. If air is treated as an ideal gas and the human body temperature is 37 °C (310 K), what is the number N oxygen molecules in a single alveolus? [Boltzmann constant k = J/K] (A) (B)(C)(D)(E)

46. The sound intensity level is defined as L = 10-log10(1/10) with the unit dB, where I is the sound intensity in units of W/m² and I0 = W/m². If a machine generates a noise level of 84 dB, what will be the noise level if an additional identical machine is turned on? [ = 0.301] (A) 84 dB (B) 168 dB (C) 90 dB (D) 190 dB (E) 87 dB

47. Two stars of masses M and 2M are in a binary star system, orbiting a common center of mass. Which of the following statements is true about their orbital periods? (A) The star with mass Mhas a longer orbital period. (B) The star with mass 2M has a longer orbital period. (C) Both stars have the same orbital period. (D) The orbital periods depend on the distance between the stars. (E) The orbital periods are independent of the masses of the stars.

48. A sample of gas is held in a container at a constant pressure. If the volume is halved, how will the rms (root-mean-square)-speed of the molecules change compared with the original rms-speed? (A) √2 times smaller (B) √2 times greater (C) the same (D) 2 times greater (E) 2 times smaller

49. A person with a volume of 0.08 m³ floats in fresh water (density = 1000 kg/m³). What is the buoyant force acting on the person? (Assume the acceleration due to gravity g is 10 m/s²) (A) 8000 N (B) 800 N (C) 80 N (D) 8 N (E) 0 N