下图是等离子体发电机示意图,平行金属板间匀强磁场的磁感应强度 B=0.5T,两板间距离为0.2m,要使输出电压为220V,则等离子体垂直射入磁场的速度v0=____m/s,a是发电机的____极。 (发电机内阻不计)
一天早晨的气温是﹣7℃,中午上升了11℃,晚上又下降了9℃,晚上的气温是( )
We were amused at his movements in doing morning exercises.