Question

With increase in frequency of an $\text{AC}$ supply, the impedance of an $\text{LCR}$ series circuit

• A. Remains constant
• B. Decreases
• C. Increases
• D. Decreases at first, becomes minimum and then increases.

Answer 1

The correct option is C Increases

The impedance of an $RLC$ circuit is given by,

$Z=\sqrt{R^2+(X_L-X_C{)}^2}$

Here,
$X_L=2\pi fL$ and $X_C=\frac{1}{2\pi fC}$

$\Rightarrow X_L\propto f$ and $X_C\propto \frac{1}{f}$

$\therefore f\uparrow X_L\uparrow X_C\downarrow$

$\Rightarrow (X_L-X_C)$ will increase and hence, $Z$ will increase.

Hence, option $\left(C\right)$ is correct.