==> 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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