用伏安法测电源电动势和内电阻的电路有两种方式：如图１、图２所示。习惯让人们将图１称为电流表内接法，将图２称为电流表外接法。由于电表内阻的非理想化———即实验原理的不完善而引起系统误差。这就迫使我们在教学生做该实验时，不得不提出这个问题，并进而加以分析和解? There are two ways to measure the voltage of the electromotive force and the internal resistance by volt-ampere measurement: as shown in Fig.1 and Fig.2. It is customary for people to refer to Figure 1 as an ammeter in-line method and Figure 2 as an ammeter external method. Due to the non-idealization of the internal resistance of the meter, ie the imperfect experimental principle, the system error is caused. This forced us to ask this question when teaching students to do the experiment, and then analyze it and solve it.