Question

With increase in frequency of an ac supply, the impedance of an $L-C-R$ series circuit

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

Answer 1

The correct option is B increases

We know that in an L-C-R circuit impedance is given by,
$Z=\sqrt{R^2+{(X_L-X_C)}^2}$
When $X_L=\omega L$ is less than $X_C=1/\omega C$
With increase in $\omega$ impedance decrease and become minimum when $X_L=X_C$
After that $X_L=\omega L$ will be greater than $X_C=1/\omega C$