4.5正弦稳态电路的功率 例2.如图电路，已知U=100V,I=100mA,电路吸收的功率P =6W,X1=1.25k2,Xc=0.45k2。电路呈感性，求r和XL c0s0= P6=0.6 UI 10 由于电路呈感性，故0=53.13° Z=D53.13?103?0.6j103?0.8600+j800 U Z1=Z-jX1=600+j800-j1250=600-j450 由于 1 11 五，-xcZ, Z, ZX。=(600-j450)j450-(600-j450j450=337.5+j450 Z+Xc600-j450+j450 600 r=337.52,X=4502例2. 如图电路，已知U = 100V，I = 100mA，电路吸收的功率P = 6W，XL1 = 1.25kΩ， XC = 0.45kΩ。电路呈感性，求r和XL。 j XL1 j XL - jXC r U I  0.6 1 0 6 cos = = = U I P  由于电路呈感性，故θ= 53.13° 3 3 53.13 10 0.6 10 0.8 600 800 U Z j j I = ? ? ? + Ð Z1 = Z – jXL1 = 600 + j800 – j1250 = 600 – j450 由于 C Z r Z j X 1 1 1 1 + − = r = 337.5 Ω， XL = 450 Ω 4.5 正弦稳态电路的功率 Z Z1 Zr 1 1 (600 450) 450 (600 450) 450 337.5 450 600 450 450 600 C r C Z jX j j j j Z j Z jX j j − − = = = = + + − +