一、论述证明题例1:如图所示,质量为m、边长为L的正方形线框abcd,从垂直纸面向里的水平有界匀强磁场的上方h高度处由静止自由下落,磁场高度为H,线框下落过程中始终在同一竖直平面内且cd边与磁场边界都沿水平方向。请证明线框进入磁场的过程中任意时刻线框克服安培力做功的功率等于线框的电功率。 I. Proof of Proof Example 1: As shown in the figure, a square wire frame abcd with a mass of m and a side length of L is free to fall from a stationary position at the height h above the horizontally bounded uniform magnetic field from the vertical paper inward. The height is H, the wireframe is always in the same vertical plane during the falling process, and the cd edge and the magnetic field boundary are in the horizontal direction. Please prove that the power of the wireframe to overcome the Ampere force at any time during the process of the wireframe entering the magnetic field is equal to the power of the wireframe.