错解分析:解题时只注重了公式的数学形式,没有理解实际的物理过程.实际上,当R_2阻值为零时,电路中电流最大,为0.6安;而当R_2阻值为最大值20欧时,电路中电流最小,为0.2安.即随着R_2阻值的增大,通过R_2的电流I_2减小,故我们无法直接根据公式U_2=I_2R_2确定在什么情况下R_2,两端的电压(即电压表示数)最大。电压表示数的变化规律可根据串 Misunderstanding analysis: When solving a problem, it only pays attention to the mathematical form of the formula and does not understand the actual physical process. In fact, when the R2 resistance is zero, the current in the circuit is the largest, 0.6 A, and when the R2 resistance is the maximum value. At 20 ohms, the current in the circuit is at a minimum of 0.2 amps. That is, as the resistance of R2 increases, the current I_2 through R_2 decreases, so we cannot determine the voltage at both ends of the R_2 directly under the formula U_2=I_2R_2. (ie, the number of voltage indications) is the largest. The number of voltage changes can be based on string