一、问题的提出供山西省课程改革试验同步试用的《教学目标与检测》一书中 ,有如下一道习题 .如图 1图 1所示 ,有一恒定电流 I流过长方体金属块 ,金属块置于与其垂直的匀强磁场 B中 ,则金属块的上、下表面哪个表面电势高 ?这道习题与 2 0 0 0年高考理科综合能力测试 (江、浙、 First, the problem proposed for the Shanxi Province curriculum reform trial trial “teaching objectives and testing” a book, there is a problem as follows. As shown in Figure 1 Figure 1, there is a constant current I flow through the cuboid metal block, metal block home In the homogeneous magnetic field B perpendicular to it, which of the surface potentials of the upper and lower surfaces of the metal block is high? This exercise and the comprehensive ability test of the 2001 college entrance examination science (Jiang, Zhe,