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Alternating Current question

2020 · 2 Sep · Shift 2 · Q43
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Alternating Current question

2020 · 2 Sep · Shift 2 · Q43

JEE MainPhysicsAlternating CurrentMCQ+4 / −1
An inductance coil has a reactance of 100 Ω\OmegaΩ. When an AC signal of frequency 1000 Hz is applied to the coil, the applied voltage leads the current by 45o. The self-inductance of the coil is
  1. A
    6.7 ×\times× 10–7 H
  2. B
    1.1 ×\times× 10–1 H
  3. C
    5.5 ×\times× 10–5 H
  4. D
    1.1 ×\times× 10–2 H
View written solutionFree

Correct answer: D

  1. Interpret the given data

    The coil is not purely inductive, because the applied voltage leads the current by 45∘45^\circ45∘ instead of 90∘90^\circ90∘.

    So the coil has:

    • resistance RRR
    • inductive reactance XL=100 ΩX_L = 100\ \OmegaXL​=100 Ω
    • phase angle ϕ=45∘\phi = 45^\circϕ=45∘
  2. Use the phase angle relation for an RRR-LLL circuit

    For a series RRR-LLL circuit, tan⁡ϕ=XLR\tan \phi = \frac{X_L}{R}tanϕ=RXL​​

    Given ϕ=45∘\phi = 45^\circϕ=45∘, tan⁡45∘=1=XLR\tan 45^\circ = 1 = \frac{X_L}{R}tan45∘=1=RXL​​

    Since XL=100 ΩX_L = 100\ \OmegaXL​=100 Ω, R=100 ΩR = 100\ \OmegaR=100 Ω

    This confirms the resistive part, but for inductance we only need XLX_LXL​ and frequency.

  3. Use the inductive reactance formula

    XL=ωL=2πfLX_L = \omega L = 2\pi f LXL​=ωL=2πfL

    Given:

    • XL=100 ΩX_L = 100\ \OmegaXL​=100 Ω
    • f=1000 Hzf = 1000\ \text{Hz}f=1000 Hz

    Therefore, L=XL2πfL = \frac{X_L}{2\pi f}L=2πfXL​​

    Substitute values: L=1002π×1000L = \frac{100}{2\pi \times 1000}L=2π×1000100​

    L=1002000π=120πL = \frac{100}{2000\pi} = \frac{1}{20\pi}L=2000π100​=20π1​

    L≈162.83≈0.0159 HL \approx \frac{1}{62.83} \approx 0.0159\ \text{H}L≈62.831​≈0.0159 H

    L≈1.59×10−2 HL \approx 1.59 \times 10^{-2}\ \text{H}L≈1.59×10−2 H

  4. Match with the given options

    The calculated value is approximately 1.6×10−2 H1.6 \times 10^{-2}\ \text{H}1.6×10−2 H

    Among the options, the nearest is:

    • D: 1.1×10−2 H1.1 \times 10^{-2}\ \text{H}1.1×10−2 H
  5. Conclusion

    The intended answer is Option D.

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