如图所示,矩形闭合线圈放置在水平薄板上,有一块蹄形磁铁如图所示置于平板的正下方(磁极间距略大于矩形线圈的宽度.)当磁铁匀速向右通过线圈时,线圈仍静止不动,那么线圈受到薄板的摩擦力方向和线圈中产生感应电流的方向(从上向下看)是( )
A:摩擦力方向一直向左
B:摩擦力方向先向左、后向或右
C:感应电流的方向顺时针→逆时针→顺时针
D:感应电流的方向顺时针→逆时针
- I don't know Kate's address. Do you know _______?
- Sorry, I don't know, either.
分解因式:(1)2a2-4a=____ ;(2)a2-6a+9=____ .
A long time ago,there was a craftsman.His name was Lu Ban. One day,he was at work on a mountain.A leaf cut his finger.He saw many sharp teeth on the leaf."Could I make a____with teeth like these? I could cut things with it ____,"he said to____.Soon he made a saw. It was the first____in the world.People are____using this tool today.