论文部分内容阅读
我们认为,高考1978年第七题和1989年第32题的命题、题解,有可商榷之处,而很多高中物理参考书上也都有类似这样的题目和题解。 1978年第七题:如图1所示,一个U形导体框架,宽度l=1米,其所在平面与水平面交角α=30°,其电阻可以忽略不计。设匀强磁场与U形框架的平面垂直,磁感应强度B=0.2特斯拉。今有一条形导体ab,其质量m=0.2千克,其有效电阻R=0.1欧姆,跨放在U形框架上,并且能无摩擦地滑动。求: (1)导体ab下滑的最大速度v_m; (2)在最大速度v_m时,在ab上释放出来的电功率。所提供的题解如下: (1)感应电动势=Blv。
We think that the propositions and solutions to the seventh question of the college entrance examination in 1978 and the 32nd question in 1989 are arguable. Many high school physics reference books also have similar questions and solutions. In 1978, the seventh question: As shown in Figure 1, a U-shaped conductor frame, width l = 1 meter, its plane and the horizontal plane angle α = 30 °, its resistance can be ignored. The uniform magnetic field is perpendicular to the plane of the U-shaped frame, and the magnetic induction intensity B=0.2 Tesla. There is a strip-shaped conductor ab, whose mass m is 0.2 kg, and whose effective resistance R is 0.1 ohms, straddles the U-shaped frame, and can slide without friction. Seeking: (1) The maximum speed v_m at which the conductor ab slides; (2) The electric power released at ab at the maximum speed v_m. The solutions provided are as follows: (1) The induced electromotive force = Blv.