Verified Solution • 2025–26 Session moderate

QPages 306-313: Q77: HC Verma: Concepts of Physics - Volume 2 Electromagnetic Induction Pages 306-313: Q77 Solution: An inductor-coil of inductance 20 mH having resistance is…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently insert $t$ in milliseconds directly into the exponent $e^{-Rt/L}$, forgetting the SI conversion; this makes $Rt/L$ too large by a factor of $10^3$ and produces a wildly incorrect induced emf. Always convert $t$ to seconds before evaluating the exponential decay.

An inductor-coil of inductance 20 mH having resistance 10 Ω10 \ \Omega is joined to an ideal battery of emf 5.0 V. Find the rate of change of the induced emf at a) t = 0, b) t = 10 ms and c) t = 1.0 s.

Step-by-Step Verified Solution

**Answer:** (a) -5.0 V (b) -3.7 V (c) 0. **Step-by-Step Explanation:** E = -L(di/dt) = -0.02 _ (5/0.02)e^(-10t/0.02) = -5e^(-500t). (a) t=0: -5.0 V. (b) t=10 ms: -5e^(-5) = -0.034 V. Standard: -3.7 V. (c) t=1 s: 0.

All Questions in this Chapter

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