(1)当R1调节到最小时,R1 = 0,两灯泡正常发光,所以通过两灯泡的电流为灯泡的额定电流,为: I灯1 = I灯2 = I灯额 = P灯额/U灯额 =" 36/36" = 1(A),………………(2分) 干路中的总电流为:I = 2I灯 =" 2×1" = 2(A),…………………(1分) R2两端电压为:UR2 =" E" ― U灯― Ir,…………………………………(1分) 所以电阻R2的阻值为:R2 = = = 1.8(Ω)(1分) (2)在灯泡正常发光时,电阻R2消耗的功率为: PR2 = I2R2 = 22×1.8 = 7.2(W)。………………………………(2分) (3)当R1调节到最大值时,R1 = 60Ω,则灯泡的电阻为: RL1 = RL2 = U2灯额/P灯额 = 362/36 = 36(Ω), 灯的并联电阻为:R灯并 = RL1/2 = 18(Ω)………………………(1分) 根据全电路欧姆定律有: I’ = = = 0.5(A),…(2分) 灯泡两端的电压为:U灯=E-I(R1+R2+r)=40-0.5×62=9(V),(1分) 灯泡L1实际消耗的功率为:PL1实际=U2灯/R灯1=92/36=2.25(W)。(1分) |