4 9、一长直导线通有电流I,旁边放置一个正方形线圈,几何尺寸及与长直导线的相对位置-|||-如下图所示,当长直导线中通有电流 =(I)_(0)sin omega t 时,求线圈中感应电动势的大小为:-|||-4-|||-心-|||-I a-|||-a a-|||-(5.0分)-|||-A、 dfrac ({10)^2(I)_(0)aomega cos (3)^t}(2pi )(ln )^2(m)^3-|||-B dfrac ({mu )_(0)(I)_(0)acos theta }(2pi )ln 2-|||-dfrac ({mu )_(0)(I)_(0)acos omega }(2pi )ln 3-|||-D dfrac ({mu )_(0)(I)_(0)acos theta }(2pi )ln at