Labour party recommended certain measures to their constituents, and the event proved their wisdom; yet it is fresh in our memories how soon the press began to teem with pamphlets and weekly papers against those very meadures.
【简答题】如图 4 所示, abcd 为一边长为 l 的正方形导线框,导线框位于光滑水平面内,其右侧为一匀强磁场区域,磁场的边界与线框的 cd 边平行,磁场区域的宽度为 2 l ,磁感应强度为 B ,方向竖直向下.线框在一垂直于 cd 边的水平恒定拉力 F 作用下沿水平方向向右运动,直至通过磁场区域. cd 边刚进入磁场时,线框开始匀速运动,规定线框中电流沿逆时针方向为正,则导线框从刚进入磁场到完全离开磁场...