12. An electron in the hydrogen atom makes a transition from the n=5 level to the n=2 level. What is the wavelength of the emitted photon? （q_e = –1.60×10⁻¹⁹ C, h=6.63×10⁻³⁴ J·s）
(A) 326 nm
(B) 435 nm
(C) 578 nm
(D) 662 nm
(E) 769 nm

8. A magnetic field given by B（t）=0.2t - 0.5t2 T is directed perpendicular to the plane of a circular coil containing 25 turns of radius 1.8 cm and whose total resistance is 1.5Ω . What is the power dissipation at 3 s ? (A) 2.28 mW (B) 3.38 mW (C) 4.52 mW (D) 5.56 mW (E) 6.72 mW

9. Suppose that the temperature at the center of the Sun is 2.00×107 K, what is the average translational kinetic energy of a proton in the Sun’s center? （kB=1.3810−23 × J/K） (A) 1.38×10−16J (B)4.14×10−16J (C) 5.52×10−16J (D) 7.64×10−16J (E) 8.96 ×10−16J

10. A nonconducting sphere of radius 10 cm has charge uniformly distributed throughout its volume. The electric field is directed radially outward and its strength at 5 cm from the center is 2000 N/C. What is the volume charge density of the sphere? (∈0 =8.85×10−12C2 /N·m 2 ）. (A) 1.06 µC/m3 (B) 2.12 µC/m3 (C) 3.16 µC/m3 (D) 4.06 µC/m3 (E) 5.18 µC/m3

11.When radiation of wavelength 350 nm is incident on a surface, the maximum kinetic energy of the photoelectrons is 1.2 eV. What is the stopping potential for a wavelength of 230 nm?（ h=6.63×10−34 J·s, qe = –1.60×10−19  C, c=3×108 m/s） (A) 1.65 V (B) 2.04 V (C) 2.55 V (D) 3.05 V (E) 4.82 V

13. A proton is projected toward a fixed nucleus of charge +Ze with velocity V0 . Initially the two particles are very far apart.When the proton is at a distance R from the nucleus, its velocity has decreased to1/2 V0 .How far from the nucleus will the proton be when its velocity has dropped to1/4 V0? (A) 1/16 R (B) 1/4 R (C) 1/2 R (D) 4/5 R (E) 6/7 R

14. An important observation that led Bohr to formulate his model of the hydrogen atom was the fact that . (A) the emission of light by an atom did not appear to conserve energy. (B) electrons were found to have a wave nature. (C) the peak of the blackbody radiation moved to shorter wavelengths as the temperature was increased. (D) neutrons formed a diffraction pattern when scattered from a nickel crystal. (E) a low density gas emitted a series of sharp spectral lines.

15. If the peak electric field in an electromagnetic wave is 1200 V/m , what is the peak magnetic field for the same wave? (A)2.2×10−6T  (B)3.4×10−6T (C)4.0 ×10−6T(D)8.7×10−6T (E)9.6×10−6T

16. The square plates of a 9000 pF capacitor measure 90 mm by 90 mm and are separated by a dielectric which is 0.29 mm thick. The voltage rating of the capacitor is 300 V. The dielectric strength of the dielectric, in kV/m , is closest to . (A) 930 (B) 1000 (C) 1100 (D) 1200 (E) 1300

17. Electromagnetic standing waves are set up in a conducting cavity resonator in the form of a hollow metal box. The waves bounce back and forth between two parallel surfaces separated by 0.8 cm. What is the minimum resonant frequency for such a resonator? (A) 3.30 GHz (B) 4.42 GHz (C) 12.4 GHz (D) 15.5 GHz (E) 18.8 GHz

18. The potential energy function of a particle moving in one dimension is U=kx2e−x2/a2where  a = 7.50nm . At what value of x is a point of stable equilibrium located? (A) 6.81 nm (B) 7.50 nm (C) 7.80 nm (D) 11.03 nm (E) 12.62 nm