2008年全国高考Ⅱ卷理综试卷的第24题,综合性地考查了电磁感应、安培力、电流热效应等相关知识,尤其是对电流的有效值与平均值的考查,真是让人有“耳目一新”之感,非常值得回味.现将本人对此题的一点粗浅认识,与广大同仁探讨.图1原题.如图1所示,一直导体棒质量为m、长为l、电阻为r,其两端放在位于水平面内间距也为l的光滑平行导轨上,并与之密接;棒左侧两 2008 National Record II exam papers Volume 24, a comprehensive examination of the electromagnetic induction, ampere, current thermal effects and other related knowledge, especially the current RMS and the average of the test, really make people have “ Refreshing ”sense, very memorable. Now I am a little superficial understanding of this issue, with the majority of my colleagues to explore .Figure 1 original title. As shown in Figure 1, has been the quality of the conductor rod m, length l, the resistance is r, the ends of which are placed on smooth parallel rails with a spacing of 1 in the horizontal plane;