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AIIMS 201926 May
Exam
AIIMS
Year
2019
Date
26 May
Subject
Physics
Chapter
Electromagnetic Induction

AIIMS 2019 · 26 May · Physics · Electromagnetic Induction

A uniform coil of self-inductance 1.8 × 10^ -4 H and resistance 6...

A uniform coil of self-inductance 1.8×10−4H1.8 \times 10^{-4} \mathrm{H} and resistance 6Ω6 \Omega is broken up into two identical coils. These two coils are then connected in parallel across a 12 V12 \mathrm{~V} battery. The circuit time constant and steady state current through the battery respectively are

Options

  1. A30μs,8 A30 \mu \mathrm{s}, 8 \mathrm{~A}
  2. B30 ms,8 mA30 \mathrm{~ms}, 8 \mathrm{~mA}
  3. C30 s,8 A30 \mathrm{~s}, 8 \mathrm{~A}
  4. D300 s,800 A300 \mathrm{~s}, 800 \mathrm{~A}

Correct answer

A. 30μs,8 A30 \mu \mathrm{s}, 8 \mathrm{~A}

Step-by-step solution

When coil is broken into two identical parts, then resistance of each part R′=R2=62=3ΩR^{\prime}=\frac{R}{2}=\frac{6}{2}=3 \Omega Inductance of each part L′=L2=1.82×10−4=0.9×10−4HL^{\prime}=\frac{L}{2}=\frac{1.8}{2} \times 10^{-4}=0.9 \times 10^{-4} \mathrm{H} Now, time constant τ=L′R′\tau=\frac{L^{\prime}}{R^{\prime}} τ=L2×R2=LR=1.8×10−46=30μs\tau=\frac{L}{2 \times \frac{R}{2}}=\frac{L}{R}=\frac{1.8 \times 10^{-4}}{6}=30 \mu \mathrm{s} Now, effective resistance when both coils are connected in parallel R′′=R′×R′R′+R′=3×33+3=96ΩR^{\prime \prime}=\frac{R^{\prime} \times R^{\prime}}{R^{\prime}+R^{\prime}}=\frac{3 \times 3}{3+3}=\frac{9}{6} \Omega So, maximum current drawn from battery I=VR′′=129/6=8 AI=\frac{V}{R^{\prime \prime}}=\frac{12}{9 / 6}=8 \mathrm{~A}
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