JEE Main · 2022 · 25 Jul 2022 · Shift 1 · Alternating Current

To increase the resonant frequency in series LCR circuit,

(A)Source frequency should be increased
(B)Another resistance should be added in series with the first resistance.
(C)Another capacitor should be added in series with the first capacitor✓ Correct
(D)The source frequency should be decreased

Answer: (C)

Solution

The resonant frequency of a series LCR circuit is:

f = \frac{1}{2 π L C}

To increase

f

, we need to decrease the product

L C

.

Adding another capacitor in series decreases the effective capacitance (

\frac{1}{C _{eff}} = \frac{1}{C _{1}} + \frac{1}{C _{2}}

), which decreases

L C

and thus increases the resonant frequency.

Note: Changing the source frequency does not change the resonant frequency of the circuit itself.

JEE Main · 2022 · 25 Jul 2022 · Shift 1 · Single correct option