A 12 V battery is connected to a coil of resistance 6 Ω. The steady current is interrupted in 1 ms and the induced emf across the coil is 20 V. The inductance is:
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Question

A 12 V battery is connected to a coil of resistance 6 Ω. The steady current is interrupted in 1 ms and the induced emf across the coil is 20 V. The inductance is:

G1 Physics · Accepted Answer

Steady current in the coil is I = V/R = 12/6 = 2 A When the switch is opened, current changes from 2 A to 0 in Δt = 1 ms = 10⁻³ s Using |e| = L |ΔI/Δt| 20 = L × (2/10⁻³) Therefore, L = (20 × 10⁻³)/2 = 10 × 10⁻³ H = 10 mH Hence option B.