試題詳解

21.A dipole for which p m is in a uniform field E 7 10⁴ N /C  . What is the external work needed to rotate the dipole from alignment with the field to angle 60° to the field? ( cos60 ^o 0.5;sin 60^o 0.9   )
(A)
(B)  
(C)  
(D)
(E)