4. When a charged particle (charge q and mass m) moves with velocity u through a region of space where both electric field E and magnetic induction field B are present. The charged particle would experience a force F. In vector form, the force is
(A) F=qE+uxB
(B) F=qExB
(C) F=qu(E.B)
(D) F=q(E+uxB) .
阿摩線上測驗
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