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Question

A solenoid of 500 turns per meter and area 0.01 m² has a current change from 3 A to 0 A in 0.5 s. What
is the self-induced emf? (\( \mu_0 = 4\pi \times 10^{-7} \, \text{H/m} \))

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Explanation

**Energy in inductor** cannot change instantaneously because that would require infinite power, current through inductor continuous, voltage may jump, principle used in chokes, inductive kick, back emf, explaining why inductor opposes change in current. L = μ₀ n² A l , assume l = 1 m . L = 4π × 10⁻⁷ × (500)² × 0.01 × 1 = 0.00314 H . ε = L (Δ I/Δ t) = 0.00314 × (0 - 3/0.5) = 0.01884 V ≈ 0.019 V . Using Φ = B A cosθ, e = -N dΦ/dt = -N A dB/dt = B l v = N B A ω sinωt,

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