A conducting sphere of radius R and charge Q covered by a dieletric spherical shell of dieletric constant k with outer radius 2R 问:How much energy is needed to build up this electrical field distribution? 这题只有答案 没有算式 但我算的跟答案有些许不同 有没有空闲的大大要帮我CHECK一下哪里有问题? 我是用能量密度法来算的 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个再相加..... Q^2 不过答案是给 ----------(1/2 + 1/K) 16πεR 先谢了～ --

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