Lecture_17

Lecture_17 - D 22.8 Mutual and Self Induction Let’s place...

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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 (primary coil) and the other to a voltmeter (secondary coil): The primary coil creates a 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 Δ Φ Δ Φ Δ Φ Δ Φ 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 s is the number of turns in the secondary coil. P I ∝ 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 . We can substitute this into Faraday’s Law: t N s s Δ ΔΦ- = ε t N s s Δ Φ Δ- = ) ( t MI P Δ Δ- = ) ( t I M P Δ Δ- = t I M P s Δ Δ- = ⇒ ε Now it’s easy to see that the induced emf in the secondary coil depends on the changing current in the primary coil. Units? [ ] [ ] H Henry → → ⋅ A s V 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 produces a change in mag....
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Lecture_17 - D 22.8 Mutual and Self Induction Let’s place...

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