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

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

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? （qe = –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

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.

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

19. A proton with speed  v = 3.00×105m/s orbits just outside a charged sphere. The radius of the orbit is 1.0 cm. What is the charge on the sphere? (The mass of a proton is 1.67×10−27kg.) (A)1.04×10−9C  (B)3.47×10−8C (C)6.23×10−8C (D)6.50×10−8C (E)8.28×10−7C

20. A 1.0µF capacitor with an initial stored energy of 0.50 J is discharged through a 1.0 MΩ resistor. What is the current through the resistor when the discharge starts? (A)1.0×10−3A  (B)2.0×10−3A  (C)1.0×10−2A  (D)2.0×10−2A  (E)5.0×10−2A 

21. A hollow sphere of inner radius 8.0 cm and outer radius 9.0 cm floats half-submerged in a liquid of density 800kg/m3 . What is the density of the material of which the sphere is made? (A)1.1×103kg/m3  (B)1.3×103kg/m3(C)1.8×103kg/m3 (D)2.4×103kg/m3 (E)4.8×103kg/m3