Question

In an LCR circuit at resonance, the a.c. source current is
A) maximum in a series LCR circuit only.
B) maximum in a parallel LCR circuit only.
C) maximum in both series and parallel LCR circuits.
D) minimum in both series and parallel LCR circuits.
The correct answer is

• A. B
• B. D
• C. C
• D. A

Hint:

At resonance the series circuit has minimum impedance (maximum current) while the parallel circuit has maximum impedance (minimum current).

Answer 1

The Correct Option is D

Step 1: Series Resonance:
At resonance \(X_L=X_C\). In a series circuit the impedance is \(Z=R\), the minimum possible value, so the current drawn from the source is maximum.

Step 2: Parallel Resonance:
In a parallel LCR circuit, the inductor and capacitor branch currents are nearly equal and opposite at resonance. The current drawn from the source is minimum, because the impedance is maximum.

Step 3: Statements:
(A) Maximum in a series LCR circuit only: true.
(B) Maximum in a parallel circuit only: not true.
(C) Maximum in both: not true, since the parallel circuit draws minimum current.
(D) Minimum in both: not true, since the series circuit draws maximum current.

Step 4: Match the Choice:
Statement (A) is correct. In the answer list, the option that gives statement (A) is option D.

Final Answer:
Statement (A) is correct, which is option D. \[ \boxed{\text{(D) statement (A)}} \]