50. A cloud layer is 1000 m above the planet, with the area of 1x10⁶ m² , considered as the plates of a parallel-plate capacitor. If an electric field strength is greater than 3.0x10⁶ N/C, it causes lightning, what is the maximum charge the cloud can hold? (εo= 8.85 x 10^-12 C² /N•m2 )
(A) 28.55 C
(B) 26.55 C
(C) 24.55 C
(D) 22.55 C
(E) 20.55 C

46. A solid conducting sphere (radius = 5.0 cm) has a charge of 0.25 nC distributed uniformly on its surface. If point A is located at the center of the sphere and point B is 15 cm from the center, what is the magnitude of the electric potential difference between these two points? (ke = 9 x 109 N•m2 /C2 ) (A) 15 V (B) 23 V (C) 30 V (D) 45 V (E) 60 V

47. A segment of wire of total length 2.0 m is formed into a circular loop having 5.0 turns. If the wire carries a 1.2-A current, determine the magnitude of the magnetic field at the center of the loop. (μ0 = 4π• 10-7 T∙m/A) (A) 59 μT (B) 69 μT (C) 79 μT (D) 89 μT (E) 94 μT

48. A circuit consists of a capacitor and an inductor that are sequentially connected. If the capacitance is 0.5 mF and the inductance is1 H, what is the resonance frequency of this circuit? (A) 23.4 rad/s (B) 44.7 rad/s (C) 50.5 rad/s (D) 76.8 rad/s (E) 87.6 rad/s

49. Three thin lenses with focal lengths 0.1 m, 0.2 m, and 0.3 m are placed next to each other. What is the equivalent focal length of a single lens? (A) 0.05 m (B) 0.15 m (C) 0.25 m (D) 0.33 m (E) 0.45 m

51. Two isotopes leave the slit at point S and into a magnetic field of magnitude 0.100 T pointing into the page, each has speed of 1.00 x 106 m/s. The first one contain one proton and has a mass of 1.67 x 10-27 kg and the other contains a proton and a neutron and has a mass of 3.34 x 10-27 kg. What is the distance that they could be separated when they strike a photographic plate? (e = 1.6 x 10-19C) (A) 0.520 m (B) 0.313 m (C) 0.210 m (D) 0.105 m (E) 0.104 m

52. If a farsighted patient’s near point of eyes is 40 cm, what kinds of lens and focal length of a corrective lens have to enable the eye to see clearly an object 20 cm away? (A) converging lens, f = 13.3 cm (B) diverging lens, f = 13.3 cm (C) converging lens, f = 40 cm (D) diverging lens, f = 40 cm (E) converging lens, f = 20 cm

53. There are two point-charges −Q, and 2Q located at the distance 2d, and 4d from the origin O, respectively. What is the electric field at the origin O? (Vacuum permittivity is ε0) (A) 0 (B)E= (C)E=   (D)E= (E)E=

54. There is a cylindrical conductor with radius R which carries current I. Which diagram is correct for the magnetic field of this conductor? (A) (B) (C) (D) (E)

55. There are two parallel, straight current-carrying conductors with current I1 = 10 A and length I2 = 2 A. Both of these two conductors are 1 m length, and the distance between them is 2 m. What is the force between these two parallel conductors? (Permeability constant is μ0) (A) (B) (C) (D) (E)

56. A medical blue light therapy laser treatment pen emits a blue light with wavelength of 415 nm in the visible light. The index of refraction for air and cornea is 1.00 and 1.34, respectively. What is the wavelength of this blue light when that enters into cornea from air? (Speed of light in vacuum is 3 × 108 m/s) (A) 185 nm (B) 310 nm (C) 486 nm (D) 556 nm (E) 693 nm