[理工] [電磁]平面波

看板Grad-ProbAsk作者 (biglp)時間14年前 (2011/11/18 10:07), 編輯推噓4(404)
留言8則, 2人參與, 最新討論串1/3 (看更多)
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.. 煩請各位高手指點一下 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 111.249.158.90 ※ 編輯: big1p 來自: 111.249.158.90 (11/18 10:08)

11/18 22:43, , 1F
這李長岡分類題庫的題目吧?!
11/18 22:43, 1F

11/18 22:58, , 2F
第一題記得是DKCheng的例題 10^-4是振幅 σ=0所以沒α
11/18 22:58, 2F

11/18 23:00, , 3F
εr=4是給Up的資訊 100MHz就是頻率
11/18 23:00, 3F

11/18 23:01, , 4F
寫出電場瞬時式 ax^振幅cos(ωt-βz) 上面的代一代
11/18 23:01, 4F

11/18 23:03, , 5F
對了t=0 and z=1/8代表除了上面的式外 後面還有多相角
11/18 23:03, 5F

11/18 23:05, , 6F
最後t=10^-8代進式子中 再令cos=0 寫出來就OK
11/18 23:05, 6F

11/18 23:06, , 7F
第二題 磁場消失 把t=3代進去 然後cos角度=(2n-1)pi/2
11/18 23:06, 7F

11/18 23:07, , 8F
這時三角函數項會等於0 解掉就ok
11/18 23:07, 8F
文章代碼(AID): #1EnRts9y (Grad-ProbAsk)
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文章代碼(AID): #1EnRts9y (Grad-ProbAsk)