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試卷名稱：108年 - 108 學士後西醫：物理#76808
年份：108年
科目：學士後西醫-物理
53. There are two point-charges −Q, and 2Q located at the distance 2d, and 4d from the origin O, respectively. What is the electric field at the origin O? (Vacuum permittivity is ε0) 
(A) 0
(B)E=
(C)E= 
(D)E=
(E)E=
