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)

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 $LCR$ 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.