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Alternating Current question

2025 · 7 Apr · Shift 2 · Q73
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Alternating Current question

2025 · 7 Apr · Shift 2 · Q73

JEE MainPhysicsAlternating CurrentNumerical+4 / −1
An inductor of reactance 100Ω100 \Omega100Ω, a capacitor of reactance 50Ω50 \Omega50Ω, and a resistor of resistance 50Ω50 \Omega50Ω are connected in series with an AC source of 10 V,50 Hz10 \mathrm{~V}, 50 \mathrm{~Hz}10 V,50 Hz. Average power dissipated by the circuit is ‾\underline{\hspace{2cm}}​ W.
Numerical answer
View written solutionFree

Correct answer: 1

  1. Given data
  • Inductive reactance: XL=100 ΩX_L = 100\,\OmegaXL​=100Ω
  • Capacitive reactance: XC=50 ΩX_C = 50\,\OmegaXC​=50Ω
  • Resistance: R=50 ΩR = 50\,\OmegaR=50Ω
  • AC source voltage: V=10 VV = 10\,\text{V}V=10V

For a series RLCRLCRLC circuit, average power dissipated is

P=Irms2RP = I_{\text{rms}}^2 RP=Irms2​R

So first we find the current.

  1. Net reactance

In series,

X=XL−XC=100−50=50 ΩX = X_L - X_C = 100 - 50 = 50\,\OmegaX=XL​−XC​=100−50=50Ω

  1. Impedance of the circuit

Z=R2+X2=502+502Z = \sqrt{R^2 + X^2} = \sqrt{50^2 + 50^2}Z=R2+X2​=502+502​

Z=2500+2500=5000=502 ΩZ = \sqrt{2500 + 2500} = \sqrt{5000} = 50\sqrt{2}\,\OmegaZ=2500+2500​=5000​=502​Ω

  1. Current in the circuit

Assuming the given AC voltage 10 V10\,\text{V}10V is the rms value,

Irms=VrmsZ=10502=152 AI_{\text{rms}} = \frac{V_{\text{rms}}}{Z} = \frac{10}{50\sqrt{2}} = \frac{1}{5\sqrt{2}}\,\text{A}Irms​=ZVrms​​=502​10​=52​1​A

  1. Average power dissipated

Only the resistor dissipates average power:

P=Irms2RP = I_{\text{rms}}^2 RP=Irms2​R

P=(152)2×50P = \left(\frac{1}{5\sqrt{2}}\right)^2 \times 50P=(52​1​)2×50

P=150×50=1 WP = \frac{1}{50} \times 50 = 1\,\text{W}P=501​×50=1W

  1. Final answer

1 W\boxed{1\,\text{W}}1W​

  1. Comparison with stored answer

Stored correct answer: 111

Our derived answer is also 111, so it agrees.

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