10. A resistor of unknown resistance and a 15 Ω resistor are connected across a 20 V emf in such a way that a 2 A current is observed. What is the value of the unknown resistance?
(A) 5 Ω
(B) 7.5 Ω
(C) 12 Ω
(D) 30 Ω
(E) 75 Ω

6. A hydraulic press has one piston of diameter 2 cm and the other piston of diameter 8 cm. What force must be applied to the smaller piston to obtain a force of 1600 N at the larger piston? (A) 6 N (B) 25 N (C) 100 N (D) 400 N (E) 1600 N

7. The position of a particle is given by the expression x= 4 cos( 3 πt + π), where x is in meters and t is in seconds. What is the frequency? (A) 1.0 Hz (B) 1.5 Hz (C) 3.0 Hz (D) 4.0 Hz (E) 9.4 Hz

8. The average molecular translational kinetic energy of a gas molecule is ______. (The ideal gas constant is R. Boltzmann constant is kB. Temperature of gas is T.) (A) (3/2)kBT (B) (3/2)RT (C) (1/2)kBT (D) (1/2)RT (E) (n+3)kBT/2, where n is the number of internal degrees of freedom.

9. A gas in a cylinder starts from initial state i to finial state f through 4 different paths as shown in the figure. Regarding to the heat energy, work, and internal energy, which statements is incorrect?(A) Path 1 is isobaric expansion, gas must be heated. (B) Path 2 is isothermal expansion； no work is involved in this process. (C) Path 3 is adiabatic expansion, therefore no heat transfer occurred. (D) Path 4 is isochoric cooling； heat is extracted out of gas. (E) Gas do not do work for path 4 only.

11. A conducting sphere of radius R contains a positive charge. Which figure correctly represents the magnitude of the electric field E as a function of the distance r from the center of the sphere? (A) (B)(C)(D)(E)

12. Which equation is not one of Maxwell’s equations? (A) (B) (C) (D) (E)

13. The flux of the electric fieldN/C through a 2 m2 portion of the xz plane is ______. (A) 16 N●m2 /C (B) −48 N●m2 /C (C) 48 N●m2 /C (D) −60 N●m2 /C (E) 60 N●m2 /C

14. An object is 12 cm in front of a concave spherical mirror, and the image is 3 cm in front of the mirror. What is the focal length of the mirror? (A) 0.25 cm (B) 1.5 cm (C) 2.4 cm (D) 4 cm (E) 13 cm

15. A light from medium A with refractive index (nA) enters medium B and medium C with refractive index, nB and nC respectively. Which of the followings is correct?(A) nA ＞ nB ＞ nC (B) nA ＞ nC ＞ nB (C) nB ＞ nC ＞ nA (D) nB ＞ nA ＞ nC (E) nC ＞ nA ＞ nB

16. Complete the following nuclear reaction:The □ , A and B should be: (A) He, 249 and 86 (B) C, 244 and 98 (C) C, 249 and 92 (D) C, 249 and 98 (E) He, 244 and 98