lecture17 - Physics 2102 Spring 2007 Physics 2102 Spring...

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Unformatted text preview: Physics 2102 Spring 2007 Physics 2102 Spring 2007 Lecture 17 Lecture 17 Ch30: Ch30: Induction and Inductance I Induction and Inductance I Physics 2102 Spring 2007 Jonathan Dowling QuickTimeoe and a decompressor are needed to see this picture. dA Faradays Law Faradays Law A time varying magnetic FLUX creates an induced EMF Definition of magnetic flux is similar to definition of electric flux B n dt d EMF B - = = S B dA n B ) r Take note of the MINUS sign!! The induced EMF acts in such a way that it OPPOSES the change in magnetic flux (Lenzs Law). Example Example When the N pole approaches the loop, the flux into the loop (downwards) increases The loop can oppose this change if a current were to flow clockwise, hence creating a magnetic flux upwards. So, the induced EMF is in a direction that makes a current flow clockwise. If the N pole moves AWAY, the flux downwards DECREASES, so the loop has a counter clockwise current! Example Example A closed loop of wire encloses an area of 1 m 2 in which in a uniform magnetic field exists at 30 to the PLANE of the loop. The magnetic field is DECREASING at a rate of 1T/s. The resistance of the wire is 10 . What is the induced current? P P = S B dA n B ) r 2 ) 60 cos( BA BA = = dt dB A dt d EMF B 2 = = dt dB R A R EMF i 2 = = A s T m i 05 . ) / 1 ( ) 10 ( 2 ) 1 ( 2 = = 30 n Is it clockwise or counterclockwise? Example Example 3 loops are shown....
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lecture17 - Physics 2102 Spring 2007 Physics 2102 Spring...

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