初中阶段物理学中传统的“恒压”问题在试卷上出现的频率相当之高,诸如“电源电压恒定”、“用电器两端电压保持不变”等等的提法说得很多,但某路端“电流恒定”之类的试题在试卷上出现的频率则相应较少.如果我们不能顾及后种情况问题的讨论和研究,那么当试卷 The traditional “constant pressure” problem in junior high school physics appears on the test paper at a relatively high frequency, such as “constant power supply voltage”, “maintaining constant voltage across the appliance”, etc. There is a lot to say, but the frequency of certain items such as “a constant current” on the test paper is relatively small. If we can’t take into account the discussion and research of the latter situation, then when the test paper