Obtain the resonant frequency and Q-factor of a series LCR circuit with L = 3.0 H, C = 27 μF, and R = 7.4Ω. It is desired to improve the sharpness of the resonance of the circuit by reducing its ‘full width at half maximum’ by a factor of 2. Suggest a suitable way.


Given: L = 3.0 H

C = 27 μF,


In Farad, capacitance C = 27 × 10-6F


R = 7.4Ω


Angular frequency is given by the relation:


ωR = 1/√LC


ωR = 1(√27 × 10-6F × 3 H)


On calculating, we get


ωR = 111.11 rad/s


Q factor can be calculated as follows:


Q = ωRL/R


Q = (111.11(rad/s) × 3H)/7.4(Ω)


Q = 45.0446


The sharpness of the resonance of the circuit by reducing its ‘full width at half maximum’ by a factor of 2 by reducing R to half.


i.e. R = R/2 = 7.4(Ω)/2 = 3.7Ω


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