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Faraday Induction Animation – Faraday induction Magnetism and Induction Roadmap Magnetic Flux / Induced emf Lenz’s Law Examples of Lenz’s Law Examples of Induced emf Generators Transformers

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Induction animation https://phet.colorado.edu/en/simulation/faradays-law

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Magnetism and Induction Flowchart lawchangefieldCurrentforcedirectexamples Force Law 1B →qv →F = qv x BRHR 1charge deflection picture tube Force Law 2B →il →F = il x BRHR 12 wires, motor, loudspeaker Ampere’s Law B = μ o i/2πr← iRHR 2electromagnet solenoid Faraday Induction d/dt →Φ = B*A →ε = dΦ/dt i = ε/R Lentzgenerator transformer Changing magnetic field creates current

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Magnetic flux and induced emf

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Direction of Induced Current

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Examples of Lenz’s Law – Fig 21-6 Fig 21-6 Flux down -> flux less down, change up, oppose change down, current CW Fig 21-7

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Examples of Lenz’s Law – Fig 21-9 a)Flux up -> flux less up, change down, oppose change up, current CCW b)Flux down -> flux less down, change up, oppose change down, current CW c)Flux down -> flux more down, change down, oppose change up, current CCW d)Magnetic field parallel to plane, no flux, no change in flux, no induced emf e)Flux zero, flux increasing to left, change to left, oppose change right, current CW

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Examples of Lenz’s Law – Fig a)Flux down -> flux more down, change down, oppose change up, current CCW b)Flus down -> flux less down, change up, oppose change down, current CW c)No changing flux, no induced current. d)Flux down -> flux more down, change down, oppose change up, current CCW

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Calculation of induced emf (1) Know – B = 0.6 T – Width 5 cm – 100 turns – Time 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 )

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Calculation of induced emf (2) i

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Calculation of induced emf (3)

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Other examples

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

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

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Generator and Transformer Transformer – On Primary V p = N p ΔΦ /Δt – On Secondary V s = N s ΔΦ /Δt – Since changing flux is same V s /V p = N s /N p – Power is conserved I s /I p = N p /N s – Problems 30-

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Applications – Electric generators – Car alternators – Transformers (why our power is AC) – Hard drives, magnetic tapes – Credit-card readers (why you always “swipe”)

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