推 free94531:可以請問大大B=(1/w) kX E 怎麼來的阿@@ 06/27 21:02
※ 引述《free94531 (FreeBlizzard)》之銘言：
: 題目
: http://ppt.cc/SEbF
: 告訴我算法就好了 不用真的算出來
: (a)我知道這一題是用波數(wave number)k 和w(omega)算
: 就是比較波動的公式 對吧?!@@
: (b)這題我沒什麼頭緒@@
: (c)好像是用u_av 公式算?!
: 請各位大大解答~!!!感激~!!!!!!
Problem3(15 points)
Suppose the magnetic field(B) in a plane electromagnetic wave is given by
B=jBy, where j is the unit vector along the y-direction,
By=2*10^(-7)sin(0.5*10^3*x+1.5*10^11*t)
Tesla, and the SI unit is adopted.
(a)What are the wavelength and the frequency of this electromagnetic wave?
wavelength: λ*0.5*10^3=2π λ=4π*10^(-3)
frequency: T*1.5*10^11=2π f=1/T=(1.5*10^11)/2π
(b)Write an expression for the electric field vector, including its direction.
B=(1/ω) k×E
E=iEx, where i is the unit vector along the x-direction,
Ex=60sin(0.5*10^3*x+1.5*10^11*t)
(c)What is the average intensity of this electromagnetic wave?
I=(1/2)*c*ε*60^2
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