Practice portal › Alternating Current › Resonance in Series LCR

When does the impedance of a series L–C–R (AC) circuit become minimum?

Asked in RS Academy GUJCET booklet · Resonance condition and tuning

• (1) when the resistance is equal to zero
• (2) when the impedance is equal to zero
• (3) when the electric current is equal to zero
• (4) when the imaginary part of the impedance is equal to zero

Step-by-step solution

Why the other options are wrong

• (1) The resistance is a fixed part of the circuit and does not change with frequency. The minimum of Z comes from the reactances cancelling, and that minimum is R itself, not zero.
• (2) Circular, and impossible: Z=√R²+(X_L-X_C)² can never fall below R, so it cannot become zero while the circuit has resistance.
• (3) Zero current goes with infinite impedance, the opposite extreme. At minimum impedance the current is at its maximum.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.