题目

如图所示，50匝矩形闭合导线框ABCD处于磁感应强度大小B＝／10T的水平匀强磁场中，线框面积S＝0.5m2，线框电阻不计。线框绕垂直于磁场的轴OO′ 以角速度ω＝200 rad／s匀速转动，并与理想变压器原线圈相连，副线圈接入一只“220V，60W”灯泡，且灯泡正常发光，熔断器允许通过的最大电流为10A，下列说法正确的是（    ）                                        A．中性面位置穿过线框的磁通量为零       B．线框中产生交变电压的短文改错.Dear Joe,It has been a long time since we meet last time. How’s everything going?I use to be a happy boy. As I grow up day by day, I find life is not as relaxed as before. How I miss the days which I didn’t have so much homework. I could watching TV, read magazines or do sports.But now, my parents don’t allow me do anything except my lessons. They think it is a waste of time. They say, “You’ve grow up, you should work hard to achieve your dreams.’I know they love her and all these are good for me. But I feel stressed, not knowing how to do next. Luckily, my head teacher understands me. She tells me that growing up is a long way. Facing growing pains, I have been learnt a lot. What about you, Joe?Yours, Li Hua