12. A loop of wire locates at the upper side of a long wire carrying currents of 5A. When the loop falls down toward the wire at the speed ofy, what is the direction of force exerted on the loop by the long wire at this moment?

(A) upward,
(B) downward,
(C) left,
(D) right,
(E) impossible to determine.

8. If n moles of an ideal gas are expanded isothermally from an initial volume V1 to a final volume V2, the change in entropy is (A) nRT In (V2/V1), (B) nR In (V2 /V1), (C) nkB In (V2/V1), (D) n Cp ∫dT/T, (E) n Cp/T.

9. A body oscillates with simple harmonic motion along the x axis. Its displacement varies with time according to the equation x = 5.0 sin (πt + π/3). The velocity (in m/s) of the body at t = 2.0 s is (A)+8.0, (B) -8.0, (C) -5.0, (D) -14.0, (E) +14.0.

10. Calculate the average power needed to spin a uniform, solid disk of mass 2.2 kg and radius 0.70 m from rest to 10.0 rad/s in 2.3 s.(A)9.2W,(B)11.6 W, (C) 14.0 W, (D) 12.0 W, (E) 16.4 W.

11. Two long, parallel wires, separate by 10 cm. One carries a current of 5.0 A and another carries a current of 10,0 A in the opposite direction. Which of the following statements is true?(A) In region 1, the magnetic field is into the page and is never zero. (B) In region 2, the field is into the page and is never zero. (C) In region 3, the magnetic field is into the page and is never zero. (D) In region 3, the magnetic field is out of the page and can be zero. (E) There are no points where the field is zero.

13. A Wi-Fi signal uses 5GHz frequency band for electromagnetic sinusoidal wave transmission. When the amplitude of electrical field of the EM wave is 6 V/m, what is the wave function of magnetic field B(x,t)? (u0 = 4π✖ 10-7 N/A2,ε0 = 8,85✖ 10-12F/m). (A) 5 X 107 cos(16.67x-3.14✖1010t).(B)5 X 107 cos(104.72x-3.14✖1010t). (C)2X10-8cos(16.67x-3.14✖1010t).(D)2X10-8co(104.72x-3.14X1010t). (E)0.17cos(16.67x-3.14X1010t).

14. A plane electromagnetic (EM) sinusoidal wave propagates in the x direction. Suppose the wavelength is 500.0 nm and the electrical field has an amplitude of 300.0 V/m. What is the intensity (average of poyting vector) of this EM wave (uo = 4π X 10-7N/A2,ε0= 8.85x10-12 F/m) (A)477.5 J/s.m2, (B) 337.6 J/s.m2, (C) 238.7 J/s.m2 , (D) 168.8 J/s.m2, (E) 119.4 J/s.m2.

15. The switch of this circuit is closed at t=0, what is the voltage across capacitor (Vc) after a long time (>> time constant) when the capacitor and inductor are in the steady state? (A) IV, (B) 2V, (C) 3V, (D) 4V, (E) 6V.

16. A particle with charge IC is at the origin (x = 0.0 m). A particle with charge -4C is at x = 2.0 m on the x axis. What finite value(s) of x is the electric potential zero? (A) -2 and -2/3, (B) -2 and 2/3, (C) -2/3 and 2/3, (D) -2/3 and 2/5, (E) 2/3 and 2/5.

17. The electric dipole moment of O-H bond is 5x10-30 C.m. What is the magnitude of electric dipole moment for water molecule? (sin(52.5°) = 0.79, cos(52.5°) = 0.61) (A)3.05 x 10-30 C.m.(B) 3.95 X 10-30 C.m. (C) 6.10 X 10-30 C.m.(D) 7.90 x 10-30 C.m. (E) 9.65 X 10-30 C.m.

18. An optical fiber has an index of refraction, n=1.5, and diameter, d = 10.0 um. It is surrounded by vacuum (n=1.0). When light is sent into the fiber along its axis, find the minimum outside radius, R, permitted for a bend in the fiber if no light is to escape?(A) 16.7 um, (B) 20.0 um, (C) 25.0 um, (D) 30.0 um, (E) 50.0 um.