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JEE Main 2021 (25 Feb, Shift 1) · Series LCR Circuit

Series LCR Circuit question from JEE Main 2021 (25 Feb, Shift 1)

Q50JEE Main 2021 · 25 FEB · SHIFT 1Medium

Series LCR Circuit

The angular frequency of alternating current in a L-C-R circuit is 100 rad/s. The components connected are shown in the figure. Find the value of inductance of the coil and capacity of condenser.

Figure

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Answer: (b)

  1. Current through RR: I=1560=0.25I = \frac{15}{60} = 0.25 A; the same current flows through CC.
  2. XC=100.25=40 Ω⇒C=1ωXC=1100×40=250 μX_C = \frac{10}{0.25} = 40\ \Omega \Rightarrow C = \frac{1}{\omega X_C} = \frac{1}{100 \times 40} = 250\ \muF
  3. The R′R' branch is broken (gap shown), so the full 0.25 A goes through LL: XL=200.25=80 ΩX_L = \frac{20}{0.25} = 80\ \Omega
  4. L=XLω=80100=0.8L = \frac{X_L}{\omega} = \frac{80}{100} = 0.8 H
  5. So the answer is (b) 0.8 H and 250 μ\muF.
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