Question

In the resonance condition, the current drawn from the source by a parallel resonant (L-C) circuit is:

• A. infinite
• B. zero
• C. fixed
• D. none of these

Hint:

At parallel resonance the two branch currents are equal and opposite, so the impedance is maximum and the line current is minimum.

Answer 1

The Correct Option is B

Step 1: Compare series and parallel resonance.
The key idea is that resonance makes reactances cancel, but the effect on line current is opposite for the two arrangements. In a parallel L-C tank the source sees a very high impedance.

Step 2: Think in terms of branch currents.
At resonance the capacitor branch current and inductor branch current are equal in size, \(I_L = I_C\), but they are \(180^{\circ}\) out of phase. When they meet at the source node they add up to \(I_L - I_C = 0\).

Step 3: Conclusion from cancellation.
Because the two branch currents cancel in the external line, no net current flows from the supply, even though a large current keeps oscillating inside the L-C loop.

Step 4: State the result.
Hence the current taken from the source is (ideally) zero, which is why the parallel resonant circuit is used as a rejector or band-stop element.
\[\boxed{I = 0}\]