Practice question

**Induced emf due to B change** e = -N A dB/dt, N turns, A area (m²), dB/dt rate of change of field (T/s). For 110 turns area 0.035 m² B 0.09 T to 0 in 0.5 s, dB/dt=0.18 T/s, e=110×0.035×0.18=0.693 V, direction opposes decrease via Lenz's law. ε = L (Δ I/Δ t) . Δ I = 4 - 7 = -3 A , Δ t = 0.3 s . ε = 1.5 × (-3/0.3) = 1.5 × (-10) = -15 V , magnitude = 15 V. Using Φ = B A cosθ, e = -N dΦ/dt = -N A dB/dt = B l v