【简答题】
如图所示,一根长为L的金属细杆ab绕竖直轴O<sub>1</sub>O<sub>2</sub>以角速度ω在水平面内旋转O<sub>1</sub>O<sub>2</sub>在离细杆a端L/5处若已知地磁场在竖直方向的分量为<img src="https://nimg.ppkao.com/2019-04/wangjue/2019042817180260924.jpg?sign=47d6ecb76a21f3bb05adfca656970650&t=62d5e628" />求ab两端间的电势差。<br /> <img src="https://nimg.ppkao.com/2019-04/wangjue/201904281718152814.jpg?sign=b3c71f9a6281aaaf9b3efce935899d0e&t=62d5e628" />