当开关$S_{1}$断开、$S_{2}$闭合，$L_{1}$与$L_{3}$串联，电压表$V_{1}$示数为$6V$

当开关$S_{1}$闭合、$S_{2}$断开，$L_{2}$与$L_{3}$串联，电压表$V_{1}$测量$L_{3}$两端电压，电压表$V_{2}$测量$L_{2}$两端电压

当开关$S_{1}$闭合、$S_{2}$断开，若$L_{3}$断路，则电流表示数减小为$0$，电压表$V_{1}$示数变为$3V$，电压表$V_{2}$示数变为$3V$

当开关$S_{1}$、$S_{2}$断开，三个小灯泡串联，若电压表$V_{1}$示数为$3V$，电压表$V_{2}$示数为$5V$，则小灯泡$L_{1}$两端电压为$2V$