[理工] [電磁]平面波

[big1p (biglp)]

1.
                              _   _
    A uniform plane wave with E = axEx propagates in a lossless simple medium

(εr=4, μr=1, σ=0) in the +z direction. Assume that Ex is sinusoidal with a

                                               -4
frequency 100 MHz and has a maximum value of 10  (V/m) at t=0 and z=1/8(m).

                                                                -8
Determine the locations where Ex is a positive maximum when t=10  (s).


2.

    The instantaneous expression for the magnetic field intensity of a uniform

plane wave propagating in the +y direction in air is given by

                   _   _     -6      7
                   H = az4*10  cos(10πt-ky+π/4) (A/m)

Determine the locations where Hz vanishes at t=3(ms).



對這種題目沒什麼概念..


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◆ From: 111.249.158.90
※ 編輯: big1p           來自: 111.249.158.90       (11/18 10:08)
推 popintaco:這李長岡分類題庫的題目吧?!
推 akisora:第一題記得是DKCheng的例題　10^-4是振幅　σ=0所以沒α
推 akisora:εr=4是給Up的資訊  100MHz就是頻率
→ akisora:寫出電場瞬時式 ax^振幅cos(ωt-βz)　上面的代一代
推 akisora:對了t=0 and z=1/8代表除了上面的式外　後面還有多相角
→ akisora:最後t=10^-8代進式子中　再令cos=0　寫出來就OK
→ akisora:第二題　磁場消失　把t=3代進去　然後cos角度=(2n-1)pi/2
→ akisora:這時三角函數項會等於0　解掉就ok