[電磁]
A conducting sphere of radius R and charge Q covered by a dieletric
spherical shell of dieletric constant k with outer radius 2R
問:How much energy is needed to build up this electrical field distribution?
這題只有答案 沒有算式 但我算的跟答案有些許不同
有沒有空閒的大大要幫我CHECK一下哪裡有問題?
我是用能量密度法來算的
1.r < R , E = 0
Q 2R
2.R < r < 2R , E = -------------- , Ue=∫ 1/2(kε)E^2 * 4πr^2 dr
4π(kε) r^2 R
Q^2
= -------------
16π(kε)R
Q ∞
3.r > 2R , E = ---------- , Ue=∫ 1/2(ε)E^2 * 4πr^2 dr
4πεr^2 2R
Q^2
= ------------
16π(ε)R
然後2個再相加.....
Q^2
不過答案是給 ----------(1/2 + 1/K)
16πεR
先謝了～
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