University:
Kentucky State University
Course:
PHY 212 | General Physics II
Academic year:

2020
Views:

142

Pages:

5
Author:

slypery5hy

**Ch30: Induction** **Magnetic Flux:** Φ = B.A = BAcosθ [Φ] = [B][A] = T.m² = Weber = Wb **Faraday's Law:** Ɛ_induced = -N(dΦ/dt) "Lenz's Law" dΦ/dt = { Changing "B" : dB/dt { Changing "A" : dA/dt { Rotating : d(BAcosθ)/dt = BA(-sinθ)dθ/dt Ɛ_induced = Ɛ_induced / R **Induced EMF** Induced EMF <--- Rectangle with a coil inside, labeled "Induced EMF" and "Induced Current" **Pg page 818:** Φ_B = 6t² + 7t (mWb) **a) Ɛ_induced (t = 2s)** Ɛ_induced = -N(dΦ/dt) = -d/dt (6t² + 7t) x 10^-3 = -(12t + 7) x 10^-3 At t = 2s, Ɛ_induced = -(12*2 + 7) x 10^-3 = -31 x 10^-3 V Ɛ_induced ----> +ve ⇒ Φ_B is decreasing Ɛ_induced ----> -ve ⇒ Φ_B is increasing **b) Induced Current I? Direction? R = 10 Ω** To the left, b-a I_induced = Ɛ_induced / R = |-31x10^-3| / 10 = 3.1 x 10^-3 A **Ex:** **1.** [Image of a bar magnet moving towards a coil] Φ_B increasing **2.** [Image of a bar magnet moving away from a coil] Φ_B decreasing **3.** [Image of a coil moving towards a bar magnet] Φ_B increasing **Pg page 819:** a = 2 m ε_batt = 20 V B(t) = (0.042 - 0.87t) T **a) Ɛ_induced** Ɛ_induced = -N * dΦ/dt = -d/dt (BA cosθ) = -A cosθ * dB/dt = -a²/2 * 1 * (-0.87) = 1.74 V **b) The direction of the net current is CCW** Ɛ_net = Ɛ_batt + Ɛ_induced = 20 + 1.74 = 21.74 V [Image of a square loop with sides of length 'a' and a magnetic field B perpendicular to the plane of the loop] **Pg page 819:** r = 12 cm = 0.12 m B(t) graph Ɛ_ind (0 to 2s) Ɛ_ind = -N (dΦ/dt) = -d/dt (BAcosθ) = -A cosθ (dB/dt) slope = -πr² (0.5-0 / 2-0) = 0.011 V