54. Three long wires parallel to the x axis carry currents as shown. If I = 20 A, what is the magnitude of the magnetic field at the origin point O? ( magnetic constant μ0 = 4π × 10^-7 T·m/A )
(A) 19 μT
(B) 28 μT
(C) 37 μT
(D) 47 μT
(E) 58 μT

50. A 5.0 nC point charge is embedded at the center of a nonconducting sphere (radius = 2.0 cm) which has a charge of -8.0 nC distributed uniformly throughout its volume. What is the magnitude of the electric field at a point that is 1.0 cm from the center of the sphere? (where electric constant k=9.0×109 N·m 2 /C2 ) (A) 9.0 × 104 N/C (B) 1.8 × 105 N/C (C) 2.7 × 105 N/C (D) 3.6 × 105 N/C (E) 7.2× 105 N/C

51. A 5.0 A current flows along a wire with The wire resides in a uniform magnetic field T. The magnetic force acting on the wire is described by What is the value of C+D+E? (A) 1.3 N (B) 6.3 N (C) 1.8 N (D) 4.3 N (E) 0.35 N

52. The current in an inductor (L = 40 mH) is described by with I in ampers and t in seconds. What is the magnitude of the emf induced in the inductor at t = 3.0 s? (A) 2.0 V (B) 0.080 V (C) 50 V (D) 0 V (E) 4.0 V

53. A stiff wire bent into a semicircle of radius a = 2.0 cm is rotated at constant angular speed 40 rev/s in a uniform 20 mT magnetic field. What is the amplitude of the emf induced in the loop? (A) 3.16 × 10-2 V (B) 3.16 × 10-3 V (C) 3.16 × 10-1 V (D) 1.98 × 10-2 V (E) 1.98 × 10-3 V

55. The coil shown below has 2 turns, a cross-sectional area of 0.20 m2 , and a field (parallel to the axis of the coil) with a magnitude given by B = (4.0 + 3.0t 2 ) T, where t is in s. What is the potential difference, VA - VC, at t = 3.0 s? (A) -7.2 V (B) +7.2 V (C) -4.8 V (D) +4.8V (E) -12 V

56. A series RLC circuit is connected to an ac source The resistance, capacitive reactance and inductive reactance are 40 Ω, 80 Ω, and 50 Ω respectively. What is the current () in the circuit? (A) 3.0 A (B) 0.040 A (C) 1.7 A (D) 1.4 A (E) 2.4 A

57. The rest mass of an electron isWhat is the kinetic energy of an electron with the speed of 0.80c? (The constant c is the speed of light in vacuum.) (A) (B) (C) (D) (E)

58. In the hydrogen spectrum, the ratio of the wavelengths for Lyman-α radiation (n = 2 to n = 1) to Balmer-α radiation (n = 3 to n = 2) is ______. (A)(B) (C) (D) 3 (E)

59. A sample of radioactive nuclei of a certain element can decay only by γ -emission and β -emission. If the half-life for γ -emission is 24 minutes and that for β -emission is 36 minutes, the half-life for the sample is (A) 30 minutes (B) 24 minutes (C) 20.8 minutes (D) 14.4 minutes (E) 6 minutes

60. The radioactive isotope  226Ra decays to 222 Rn with a half-life of 1600 years. The radioactive isotope  238U decays to234 Th  with a half-life of 4.5× 109 years. What is the ratio of the decay rate of 1 g  226Ra to that of 10 g238 U  ? (A) 3.0 × 106 (B) 3.0 × 10-7 (C) 3.0 × 105 (D) 3.0 × 10-6 (E) 3.0 × 107