笔者收集了一下各省市几年来的初中物理升学试卷,发现绝大多数的试卷上都有这类问题:给一个电路,并说明电路处在不同情况(某些电键的开闭、变阻器滑片的移动等)时某些物理量的数据,让考生求出另外某些未知物理量,由于电路处于不同情况时电路的联接方式一般要发生变化,所以我们就称这类问题为“变化电路”问题,例如,山西省1993年的一道中考题:如图1所示的电路,已知R_2=60Ω,电源电压不变.当K_1、K_2都接通时安培表A_1、A_2的示数分别为0.4A和0.2A;当K_1、K_2 The author has collected the junior high school physics examination papers of various provinces and municipalities for several years and found that the vast majority of examination papers have such problems: give a circuit, and explain that the circuit is in different situations (opening and closing of some keys, varistor slides When the data of some physical quantity is moved, etc.), the examinee obtains some other unknown physical quantity. Since the connection mode of the circuit is generally changed when the circuit is in different situations, we call this kind of problem a “change circuit” problem, for example, In Shanxi province in 1993, a middle exam question: The circuit shown in Fig.1 is known to have R2=60Ω, and the power supply voltage is unchanged. When K_1 and K_2 are both on, the numbers of the Amps A_1 and A_2 are 0.4A respectively. 0.2A; When K_1, K_2