如果一條iron rod用力係一條平行既wire到向右行, magnetic field 係向下..
如果張iron 轉左用copper, 甘個speed會唔會有改變?????
收錄日期: 2021-04-13 16:14:23
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20081110000051KK01485