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When the electric current in a coil changes from +2 A to -2 A in 0.05 s, an induced emf of 8.0 V is generated in it. The self-inductance of the coil is ______ H.

Asked in GSEB Board March 2016 · Self-inductance and self-induced EMF

• (1) 0.4
• (2) 0.2
• (3) 0.8
• (4) 0.1

Step-by-step solution

Why the other options are wrong

• (1) 0.4 is ε Δ t = 8.0 × 0.05 on its own: the division by the change in current (4 A) was left out.
• (2) 0.2 comes from taking the change in current as 2 A: (8.0 × 0.05)/2 = 0.2. The current reverses from +2 A to -2 A, so it changes by 4 A.
• (3) No single slip gives 0.8 H. Sanity check: with L = 0.8 H the emf would be 0.8 × 4/(0.05) = 64 V, not 8.0 V.

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