Question

In an LCR circuit R = 100 ohm. When capacitance C is removed, the current lags behind the voltage by π / 3 . When inductance L is removed, the current leads the voltage by π / 3 . The impedance of the circuit is

(a) 50 ohm

(b) 100 ohm

(c) 200 ohm

(d) 400 ohm

Answer 1

The correct option is (b) 100 ohm.

Explanation:

When C is removed circuit becomes RL circuit hence tan π/3 = XL/R ......(i)

When L is removed circuit becomes RC circuit hence tan π/3 = XC/R ......(ii)

From equation (i) and (ii) we obtain XL = XC. This is the condition of resonance and in resonance Z = R = 100Ω.