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Unformatted text preview: D 22.8 Mutual and Self Induction Let’s place two coils side by side. Let’s connect one to an AC generator rimary coil) and the other to a voltmeter (secondary coil): (primary coil) and the other to a voltmeter (secondary coil): The primary coil creates a agnetic field and some of magnetic field, and some of those field lines pass thru the secondary coil. This produces a change in magnetic flux in the secondary coil, leading to an induced emf! This is called Mutual Inductance . From Faraday’s Law: , s M s ΔΦ ∝ ε where ε s is the induced emf in the secondary coil, and ΔΦ Ms is the change in mag. flux thru the secondary coil. The net flux thru the secondary coil is: s s N Φ Where N is the number of turns in the P I ∝ s secondary coil. Thus, the flux thru the secondary coil is proportional to the current in the primary. Make this an equality: P s s MI N = Φ P s s I N M Φ = ⇒ M is a quantity called the Mutual Inductance . e can substitute this into Faraday’s Law: We can substitute this into Faraday s Law: N s s ΔΦ − = ε N s s Φ Δ − = ) ( MI P Δ − = ) ( I M P Δ − = t Δ t Δ t Δ t Δ I M P Δ − = ⇒ ε Now it’s easy to see that the induced emf t s Δ in the secondary coil depends on the changing current in the primary coil. Units? [ ] [ ] H Henry → → ⎥ ⎤ ⎢ ⎡ ⋅ s V ⎦ ⎣ A So, inductance comes in henries. 1 H is a pretty big inductance. Often use mH or μ H. Self Inductance Consider just one coil connected to an AC generator: The AC current produces a changing magnetic field which produces a change in mag. flux ithin the coil within the coil....
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 Spring '08
 BLACKMON
 Physics, Magnetic Field, Faraday's law of induction, secondary coil

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