Question

When the frequency of the $AC$ voltage applied to a series $LCR$ circuit is gradually increased from a low value, the impedance of the circuit

• A. monotonically increases
• B. first increases and then decreases
• C. first decreases and then increases
• D. monotonically decreases

Answer 1

Answer: (B)

first increases and then decreases

Answer 2

The impedance of LCR circuit
$Z=\sqrt{R^{2}+\left(\omega_{c}-\frac{1}{\omega_{c}}\right)^{2}}$
Where, $R=$ Resistance
$L=$ Inductance
$C=$ Capacitance
When frequency of AC voltage applied to a series $L C R$ circuit, it will first increase and resonance state $\omega_{L}=\frac{1}{\omega_{c}}$, it will decrease.
In that state $(Z=R)$, it will be minimum.
So, it will first increases and then decreases.