First slide
Power in a.c. circuit
Question

An LCR series circuit with a resistance of 100 ohm is connected to an ac source of 200 V (r.m.s.) and angular frequency 300 rad/s. When only the capacitor is removed, the current lags behind the voltage by 60o . When only the inductor is removed the current leads the voltage by 60o . The average power dissipated is  

 

Moderate
Solution

tanϕ=XLR=XCRtan60=XLR=XCRXL=XC=3R  i.e. Z=R2+XLXC2=R  So average power P=V2R=200×200100=400W

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