# Lect09 - 1 Lecture 9 Faraday’s Law Lenz’s Law October...

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Unformatted text preview: 1 Lecture 9: Faraday’s Law, Lenz’s Law October 11 Physics 104, Fal 2009 1 Changing Magnetic Fields create Electric Fields Inductance LR Circuit Magnetic Flux Examples October 11 Physics 104, Fal 2009 2 A conducting loop is inside a solenoid B=μnI What happens to the flux through the loop when Increase area of solenoid Increase area of loop Increase current in solenoid Rotate loop slightly about vertical axis Nothing Increases Φ = B A cos( ϕ ) Increases Decreases Magnetic Flux Examples II October 11 Physics 104, Fal 2009 3 A solenoid (B= μ nI) is inside a conducting loop. What happens to the flux through the loop when Increase area of solenoid Increase area of loop Increase current in solenoid Increases Nothing Increases Φ = B A cos( ϕ ) Faraday’s Law (Magnitude) Emf = Change in magnetic Flux/Time October 11 Physics 104, Fal 2009 4 ε = − N ΔΦ Δ t = − N Φ f − Φ i t f − t i N- is number of turns in the loop ΔΦ is change in magnetic flux Magnetic flux, Φ = B A cos( θ ) , depends on: 1. Area of loop A 2. Magnetic field B 3. Angle θ between A and B Lenz’s Law (Direction) October 11 Physics 104, Fal 2009 5 Emf opposes change in flux EMF does NOT oppose B field, or flux! EMF opposes the CHANGE in flux Direction: Lenz’s law October 11 Physics 104, Fal 2009 6 2 Change B Which way is the magnet moving if it is inducing a current as shown? 1) Up 2) Down October 11 Physics 104, Fal 2009 7 S N N S Current creates flux up. This must be opposing increase in flux down. So magnet must be falling down Change B If I reduce the resistance in the wire, the magnet will fall 1) faster 2) slower 3) at the same speed October 11 Physics 104, Fal 2009 8 S N N S Decreasing R, increases I. Increases opposing field, which makes magnet fall slower....
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## This note was uploaded on 11/30/2011 for the course PHYSICS 104 taught by Professor Dasu/karle during the Fall '11 term at University of Wisconsin.

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Lect09 - 1 Lecture 9 Faraday’s Law Lenz’s Law October...

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