The World Cup ______ every four years. And the last one _____in South Africa. A. is taken place; was held B. takes place; was held C. is taken place; held D. takes place; held 答案:B
一矩形线圈,绕垂直于匀强磁场并位于线圈平面内的固定轴转动,线圈中的感应电动势e随时间t的变化规律如图所示,下列说法中正确的是
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A.
每当e转换方向时,通过线圈的磁通量的绝对值都为最大
B.
t2时刻通过线圈的磁通量绝对值最大
C.
t3时刻通过线圈的磁通量变化率的绝对值最大
D.
t1时刻通过线圈的磁通量为零