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Induction

Induction. Demonstration – Magnetic induction Roadmap - Magnetism and Induction Magnetic Flux / Faraday Induction Lenz’s Law Examples of Lenz’s Law Examples of Induction Generators Transformers . Demonstration. Galvanometer with coil Wave magnet in front

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Induction

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  1. Induction • Demonstration – Magnetic induction • Roadmap - Magnetism and Induction • Magnetic Flux / Faraday Induction • Lenz’s Law • Examples of Lenz’s Law • Examples of Induction • Generators • Transformers

  2. Demonstration • Galvanometer with coil • Wave magnet in front • Current generated only when magnet moves • Fundamental principle behind • Generators, Alternators • Transformers • Hard drive, magnetic tapes • Credit-card swipes

  3. Magnetism and Induction Flowchart • *Changing* magnetic field (flux) creates current

  4. Faraday Induction • Magnetic Flux ΦB = Bperp A = BA cosθ • Area perpendicular to B field • Area “normal” inline with field (cos θ) • Units weber • Faraday Induction emf = - ΔΦB / Δt (single turn) emf = - N ΔΦB / Δt (multiple turn) • units T-m2/s = (N/A m) m2 /s = (J/A)/s = J/C = V

  5. Direction of Induced Current • Lenz’s Law • Induced current will create magnetic field to oppose **change** that produced it • Natural logic – things are going to reinforce change that produces them – perpetual motion! • Flux can change in 3 ways • Area • Orientation • Magnetic Field

  6. Examples of Lenz’s Law • Figure 21- 6 • Figure 21-9 • Exercise B (p 589)

  7. Calculation of emf • Example 21-5 • B = 0.6 T • Width 5 cm • 100 turns • 0.1 s • R = 100 ohms • Find • Emf, current (1.5 v 15 mA) • Force required (.045 N) • Work done by that force (2.25 mJ) • Power, Work (22.5 mW, 2.25 mJ)

  8. Other examples Φ = B A cos(θ) • Change in B • Problem 11 • Change in A • Problem 13 • Problem 17 • EMF fromFlux (0.168V) • EMF fromqvB • Current (0.168V/27.5 ohm = 6.1 ma) • Force (0.64 mN) • Change in θ • Generator

  9. Generator • Φ = BA cos(ωt) • ε = N dφ/dt • ε = NBωA sin(ωt) • Lentz’s Law • Problems 20-25 • Prob 20 (42 loops)

  10. Generator and Transformer • Transformer • On Primary • Vp = NpΔΦ /Δt • On Secondary • Vs= NsΔΦ /Δt • Since changing flux is same • Vs/Vp= Ns/Np • Power is conserved • Is/Ip= Np/Ns • Problems 30-

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