用电压表测量用电器的电压时,应将电压表与被测用电器并联 (如图1)。若电压表与被测用电器串联,就不能测出用电器的电压(如图 2)．这是因为电压表对电流的阻碍作用很大,电路中的电流非常小, 小灯泡不亮,此时小灯泡(对电流的阻碍作用远远小于电压表)相当于一根导线,电压表的负接线柱相当于与电源负极相连,电压表测的是 When using a voltmeter to measure the voltage of the appliance, the voltmeter should be connected in parallel with the appliance being tested (Figure 1). If the voltmeter is connected in series with the electrical appliance under test, the voltage of the appliance cannot be measured (see Figure 2). This is because the voltmeter has a great hindrance to the current, the current in the circuit is very small, and the small light bulb is not bright. At this moment, the small light bulb (the hindrance to the current is much smaller than the voltmeter) is equivalent to a wire, and the voltage meter is The negative terminal is equivalent to the negative terminal of the power supply. The voltage meter measures