一个矩形线圈在匀强磁场中绕垂直于磁场的转轴从中性面开始匀速转动，经过（为周期）产生的感应电动势为2V，则感应电动势的有效值为_____V．
At present there are many online courses and we can choose some to study by （we）．
Deep in his heart， Nelson Mandela wanted to help the black people to live （free）．
Miss White often has us （tell） interesting stories in her English class．
根据句意用所给单词的适当形式填空．
Look! Your room is really （tidy）． You should learn to be organized．
Qian Xuesen （consider） as "Father of Missile（导弹）in China"．
（
为周期）产生的感应电动势为2V，则感应电动势的有效值为_____V．
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