Question

An LCR series circuit with 100 W resistance is connected to an AC source of 200 V and angular frequency 300 radians per second. When only the capacitance is removed, the current lags behind the voltage by 60ŗ. When only the inductance is removed, the current leads the voltage by 60ŗ. Then the current and power dissipated in LCR circuit are respectively

• A. 1A, 200 watt
• B. 1A, 400 watt
• C. 2A, 200 watt
• D. 2A, 400 watt

Answer 1

Answer: (D)

2A, 400 watt

Answer 2

When capacitance is removed

tan q = $\frac{\omega L}{R}$ or wL = 100 tan 60⁰…(1)

when inductance is removed

tan f = $\frac{1}{(\omega C)(R)}$ or $\frac{1}{\omega C}$ = 100 tan 60⁰ ….(2)

So Z = R = 100 W

I = V/R = 200/100 = 2A

Power P = I² R = 4 × 100 = 400 W