如图1所示,两个电阻串联后接到电压为U的电源上.设电阻R_1和R_2上的电压分别为U_1和U_2.则(1)当R_1变大,而R_2不变时,串联电路的总电阻变大,电流变小.由欧姆定律可知,U_2=IR_2变小,由U_1+U_2=U可知,U_1变大. As shown in Figure 1, the two resistors are connected in series and connected to a power supply with voltage U. The voltages on the resistors R_1 and R_2 are U_1 and U_2, respectively. (1) When R_1 becomes large and R_2 does not change, the series connection The total resistance of the circuit becomes larger and the current becomes smaller. It is known from Ohm’s law that U_2=IR_2 becomes smaller, and U_1+U_2=U shows that U_1 becomes larger.