Practice question

**Solenoid carries steady current** second coil experiences emf only when current in solenoid changes because dΦ/dt ≠0 only when I changes, steady current gives constant flux, no induction, illustrating Faraday's law requires changing flux, not static field. Δ Φ = B A = 0.12 × 0.08 = 0.0096 Wb . ε = N (Δ Φ/Δ t) = 130 × (0.0096/0.4) = 130 × 0.024 = 3.12 V . Using Φ = B A cosθ, e = -N dΦ/dt = -N A dB/dt = B l v = N B A ω sinωt, L = μ₀ N²A/l, M = e/(dI/dt) and U = ½ L I²,