2005/07/17 | 电磁波[Electromagnetic Wave]
类别(Ω〖物理〗) | 评论(0) | 阅读(39) | 发表于 09:17
For traveling electromagnetic waves, the electric and magnetic fields E and B are in phase. In cgs,
(1)

(2)

(3)

(4)

and in MKS,
(5)

(6)

(7)

where is the permeability of free space. The average flux is then
(8)

For standing EM waves, E and B are 90° out of phase. In cgs,
(9)

(10)

(11)

(12)

and in MKS,
(13)

(14)

(15)

(16)

For an electromagnetic wave represented in complex notation as
(17)

the following identities hold:
(18)

(19)

(20)

The electromagnetic wave equations follow from the telegraphy equations. In free space in cgs
(21)

(22)

and
(23)

(24)

In MKS
(25)

(26)

where is the permeability of free space and is the permittivity of free space, and
(27)

(28)

In a dielectric in cgs
(29)

(30)

so using
(31)

where c is the speed of light, is the electric permittivity, is the magnetic permeability, and n is the index of refraction gives
(32)

(33)

In MKS,
(34)

(35)

so using
(36)

where is the dielectric constant and is the relative permeability gives
(37)

(38)
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