==> Beachboy.bbs@ptt.cc (天煞孤星) 提到:
>  有一題高中關於"點電荷"的選擇題是這樣的：
>  A.專指一帶電小質點
>  B.專指帶電之金屬球
>  C.指帶電體間之距離遠大於帶電體本身
>  D.指帶電體甚大於兩者間之距離
>  答案是C
>  我想問A可以選嗎
>  不能選的原因，是因為那個"專"的原因嗎？
>   thx.

   In physics, no such "single point source" exists in the real world.
   If you find a positive source somewhere, a corresponding negative
   source must exist elsewhere. :>

   if you wanna choose the answer "A", the description shall probably
   be modified to "a positive point source is located in origin of
   the Catesian coordinates, and a negative point source located
   in the infinite".
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☆ [Origin:椰林風情] [From: fiber7.ee.nthu.edu.tw] [Login: **] [Post: 10]