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When the electric current in a coil steadily changes from +2 A to -2 A in 0.05 s, an induced emf of 8 V is generated in it. Then the self-inductance of the coil is ....... H.

Asked in RS Academy GUJCET booklet · Self-inductance and self-induced EMF

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

Step-by-step solution

Why the other options are wrong

• (1) Comes from taking the change in current as 2 A: (8×0.05)/2=0.2 H. Going from +2 A through zero to -2 A is a change of 4 A.
• (2) Comes from stopping at ε Δ t=8×0.05=0.4 and never dividing by the change in current.
• (3) No single slip produces 0.8 H. Sanity check: L=(ε Δ t)/(|Δ I|)=(8×0.05)/4 fixes it at 0.1 H.

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