关于现代通信和电磁波,下列叙述正确的是( )
They considered ______ a computer ,which was considered ______ a great help in their work.
如图所示,一半径为r=10 cm的圆形线圈共100匝 ,在磁感应强度B= T的匀强磁场中,绕垂直于磁场方向的中心轴线OO′以n=600 r/min的转速匀速转动,当线圈转至中性面位置(图中位置)时开始计时.