[领域]普物 (题目相关领域) [来源]serway 6th 26-74 (课本习题、考古题、参考书...) [题目] Yoy are optimizing coaxial cable design for a major manufacturer. Show that for a given outer conductor radius b, maximum potential difference capability is attained when the radius of the inner conductor is a=b/e where e is the base of natural logarithms. [瓶颈] (写写自己的想法，方便大家为你解答) http://www.zshare.net/image/8829355f8ecef1/ (这是网路上标准答案) 但a越小电位差不是越大? 为何在题目説 a=b/e 会有最大值 而且正解的Emax不也是a的函数 在对a微分时为何没对Emax微? --

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