複選題
16. Assume two electromagnetic waves (frequency f_A and f_B) enters a nonlinear material whose polarization field includes a term that is proportional to the square of the clectric field. Which of the following frequencies could one possibly observe at the output of the nonlincar material?
(A) f_A+ f_B
(B) 2f_A
(C) 2f_B 
(D) All of the above.

12. Which of the following statements is not correct in general? (A) Diamagnetism could be related to the orbital motion of electrons. (B)Paramagnetism could be related to the electronic spin. (C) Ferromagnetism becomes obvious above the Curie temperature. (D) Antiferromagnetism vanishes above the Neel temperature.

13. Consider a sheet current source at z = 0. The medium on either side of the sheet is free space. Which of the following statements for the region z ＞0 is not correct? (A) There will be a wave propagating in the +z direction. (B) The electric field and magnetic field are in phasc. (C) The instantaneous power flow out of an arbitrary closed surface is zero. (D) The average power flow is half of the peak power flow.

14. Consider a sheet current source at z =0. The medium on either side of the sheet is perfect dielectric. Assume the dielectric constant is higher in the z ＞0 region. Which of the following statcments is not correct? (A) The power flux is higher in the z＞0 region. (B) The power flux is higher in the z ＜0 region. (C) The power flux is the same in both regions (D) There is no power flux in both regions.

15. Assume the relation holds in a medium, where ε is a constant. What do we not imply for that medium? (A) The medium is linear. (B) The medium is isotropic. (C) The medium is nondispersive. (D) The medium is lossless.

17. Consider a situation that region 1 (z ＜0) is free space and region 2 (z ＜0) is an anisotropic lossless nonmagnetic material described by the following reiationship.  For a uniforn piane wave with the electric field incident on the interface z =0 form region I. What is the electric field of the reflected wave?(A) (B)(C) (D) None of the above.

18. Following the previous question, what is the electric field of the transmitted wave? (A) (B)(C)(D) None of the above.

19. A randomly polarized electromagnetic wave in free space is incident on a lossless medium with a diclectric constant of 3. At what incident angle does the reflected wave become linearly polarized? (A) 0 degree (B) 30 degrees (C) 60 degrees(D) None

20. Assume the electron density is 106 cm-3 in a certain layer of ionsphere. Which of the following frequency of electromagnetic waves that could pass through that layer? (A) 12 MHz (B) 8 MHz (C) 4 MHz (D) 1 MHz

21.If V/m. Find (z，t). (A)mA/m (B)mA/m (C)mA/m (D)m/Am

22. In an air-filled parallel-plate waveguide with dimension a = 4 cm, according to the expression of electric field distribution, E= E0(sin25πx+3sin50πx)sin(8x109πt) What is the value of phase constantβ2 of propagation wave? (A) 7.5 (B) 23.5 (C) 29.2 (D) 74 radm