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如图所示,在平面直角坐标系中,第一象限内有竖直向下的匀强电场,场强为E=20N/C,第四象限内有一个圆形区域的匀强磁场,方向垂直纸面向外,大小为B=4 2 ,未画出来.一个带正电的粒子质量为m=2×10-5kg,电量为q=5×10-3C,重力不计,从y中上的a点以v0=10m/s的速度垂直y轴射入电场.Oa长度为h=0.01m,粒子通过x轴上的b点进入第四象限,粒子经圆形磁场后从c点射出第四象限,出射的速度方向与y轴负方向成75°.(π=3.14)求:(1)粒子通过b点时的速度大小及方向.(2)磁场的最小面积是多少.
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