Q.

A series LCR circuit containing 5.0 H inductor, 80 μF capacitor and 40 Ω resistor is connected to 230 V variable frequency AC source. The angular frequencies of the source at which power transferred to the circuit is half the power at the resonant angular frequency are likely to be    [2021]
 

1 42 rad/s and 58 rad/s  
2 25 rad/s and 75 rad/s  
3 50 rad/s and 25 rad/s  
4 46 rad/s and 54 rad/s  

Ans.

(4)

ωr=1LC=15×80×10-6=50 rad/s

Power transferred = half of power at resonance

So, frequencies at which power transferred is half =ωr±Δω    Δω=R2L=402×5=4 rad/s

So, range is ωr±Δω=50±4=54 rad/s and 46 rad/s