初中电学学习阶段,经常会遇到这样一类的习题,当电路中出现断路或短路时,电表都会有一些不同的变化,如无示数、有示数、变大、变小等.学生遇到这样习题时,总是束手无策,不知如何去判断.在教学中,我和学生通过做实验总结了这样一些规律,使学生能很快地掌握了其判断方法.一、判断方法因为电流表的电阻非常的小,可忽略,它串联在电路里相当于一根导线;电压表的电阻非常大,在电路里 In junior high school electricity learning stage, we often encounter such a class of exercises. When there are open circuit or short circuit in the circuit, there will be some different changes in the meter, such as no indication, a number, a larger, smaller and so on. In this type of exercise, I always know what to do. I do not know how to judge. In the teaching, I and students through the experiment summed up some of these laws, so that students can quickly grasp its judgment methods. First, the judgment method because of the resistance of the ammeter Very small, negligible, it is equivalent to a wire in series in the circuit; the resistance of the voltmeter is very large, in the circuit