一、一道物理习题的错解所引起的思考笔者曾用到这样一道物理习题测试学生:如图1所示,水平面上固定一个间距l=1m的光滑平行金属导轨,整个导轨处在竖直方向的磁感应强度B=1T的匀强磁场中,导轨一端接阻值R=9Ω的电阻,导轨上有质量m=1kg、电阻r=1Ω、长度也为1m的导体棒,在外力的作用下从静止开始沿平行导轨方向做匀变速直线运动,加速度a=2m/s~2,不计导轨电阻。求:(1)t=4s时导体棒受到的安培力的大小; First, a misunderstanding of physical exercises caused by thinking I have used such a physical exercise test students: As shown in Figure 1, the level of a fixed pitch l = lm smooth parallel metal rails, the entire rail in the vertical direction Of the magnetic flux density B = 1T uniform magnetic field, one end of the guide resistance R = 9Ω resistance, the guide rail has a mass m = 1kg, the resistance r = 1Ω, length of 1m conductor rod, under the action of external force from Still start along the direction of parallel rails do uniform variable speed linear motion, acceleration a = 2m / s ~ 2, excluding track resistance. Seeking: (1) the magnitude of ampere force that conductor rod receives when t = 4s;