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NEET PHYSICSMedium

A series LCR circuit containing 5.0 H5.0\text{ H} inductor, 80 μF80\text{ }\mu\text{F} capacitor and 40 Ω40\text{ }\Omega resistor is connected to 230 V230\text{ 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

A

25 rad/s25\text{ rad/s} and 75 rad/s75\text{ rad/s}

B

50 rad/s50\text{ rad/s} and 25 rad/s25\text{ rad/s}

C

46 rad/s46\text{ rad/s} and 54 rad/s54\text{ rad/s}

D

42 rad/s42\text{ rad/s} and 58 rad/s58\text{ rad/s}

Step-by-Step Solution

The resonance frequency of LCR series circuit is given as ω0=1LC=15×80×106=50 rad/s\omega_0 = \frac{1}{\sqrt{LC}} = \frac{1}{\sqrt{5 \times 80 \times 10^{-6}}} = 50\text{ rad/s}. Now half power frequencies are given as ω=ω0±R2L\omega = \omega_0 \pm \frac{R}{2L}. i.e., ωL=50402×5=46 rad/s\omega_L = 50 - \frac{40}{2 \times 5} = 46\text{ rad/s} and ωH=50+402×5=54 rad/s\omega_H = 50 + \frac{40}{2 \times 5} = 54\text{ rad/s}.

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