Question

With gradual increase in frequency of an a.c. supply, the impedance of an LCR series circuit

• A. increases
• B. decreases
• C. remains constant
• D. first decreases, becomes minimum and then increases

Hint:

Impedance falls to its minimum at resonance and then rises.

Answer 1

The Correct Option is D

Step 1: Shape of the curve:
Current in an LCR circuit peaks at resonance, so the impedance $Z = V/I$ is lowest there.

Step 2: Both sides:
Away from resonance, in either direction, $|X_L - X_C|$ grows, so $Z$ grows.

Step 3: Result:
Rising frequency takes the circuit through the minimum, option (D).

Final Answer:
Impedance falls, reaches a minimum, then rises. \[ \boxed{\text{(D) }\text{first decreases, becomes minimum and then increases}} \]