A plane-polarized electromagnetic wave is incident normally on a flat, perfectly conducting surface. Upon reflection at the surface, which of the following is true?
A. Both the electric vector and magnetic vector are reversed.
B. Neither the electric vector nor the magnetic vector is reversed.
C. The electric vector is reversed; the magnetic vector is not.
D. The magnetic vector is reversed; the electric vector is not.
E. The directions of the electric and magnetic vectors are interchanged.
EM wave: E ⊥ B (perpendicular to each other).
If E normal to the surface of conductor, B is tangential.
BC: Enormal ≠ 0 and Btangential ≠ 0
Only E is reversed.
B is not reserved, it's parallel to the surface.
Answer: C
A. Both the electric vector and magnetic vector are reversed.
B. Neither the electric vector nor the magnetic vector is reversed.
C. The electric vector is reversed; the magnetic vector is not.
D. The magnetic vector is reversed; the electric vector is not.
E. The directions of the electric and magnetic vectors are interchanged.
(GR9277 #36)
Solution:
Perfect conductor:
Its charge and current are distributed on the surface so that external fields can not penetrate it.
Boundary Condition (BC) on the surface of perfect conductor:
- Etangential = 0
- Enormal ≠ 0
- Btangential ≠ 0
- Bnormal = 0
EM wave: E ⊥ B (perpendicular to each other).
If E normal to the surface of conductor, B is tangential.
BC: Enormal ≠ 0 and Btangential ≠ 0
Only E is reversed.
B is not reserved, it's parallel to the surface.
Answer: C
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