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NEET PHYSICSMedium

An inductor 20 mH20 \text{ mH}, a capacitor 50μF50 \mu\text{F}, and a resistor 40Ω40 \, \Omega are connected in series across a source of emf V=10sin(340t)V = 10\sin(340t). The power loss in the AC circuit is:

A

0.67 W

B

0.78 W

C

0.89 W

D

0.46 W

Step-by-Step Solution

From the given voltage equation V=10sin(340t)V = 10\sin(340t), the peak voltage is Vm=10V_m = 10 V and the angular frequency is ω=340\omega = 340 rad/s. The inductive reactance is XL=ωL=340×20×103=6.8ΩX_L = \omega L = 340 \times 20 \times 10^{-3} = 6.8 \, \Omega. The capacitive reactance is XC=1ωC=1340×50×106=10.01758.82ΩX_C = \frac{1}{\omega C} = \frac{1}{340 \times 50 \times 10^{-6}} = \frac{1}{0.017} \approx 58.82 \, \Omega. The impedance of the series LCR circuit is Z=R2+(XCXL)2=402+(58.826.8)2=402+52.0221600+2706=430665.62ΩZ = \sqrt{R^2 + (X_C - X_L)^2} = \sqrt{40^2 + (58.82 - 6.8)^2} = \sqrt{40^2 + 52.02^2} \approx \sqrt{1600 + 2706} = \sqrt{4306} \approx 65.62 \, \Omega. The RMS current is Irms=VrmsZ=Vm/2Z=102×65.62I_{rms} = \frac{V_{rms}}{Z} = \frac{V_m / \sqrt{2}}{Z} = \frac{10}{\sqrt{2} \times 65.62}. The power loss in the circuit is dissipated only in the resistor and is given by P=Irms2RP = I_{rms}^2 R . P=(102×65.62)2×40=1002×4306×40=200043060.46P = \left( \frac{10}{\sqrt{2} \times 65.62} \right)^2 \times 40 = \frac{100}{2 \times 4306} \times 40 = \frac{2000}{4306} \approx 0.46 W.

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