PHY108 - Chapter 30

# PHY108 Chapter 30 - Ch 30 Faradays Law We have demonstrated that a magnetic field can be produced by either a moving charged particle currents or

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Ch. 30: Faraday’s Law Faraday’s Law of Induction Motional EMF Lenz’s Law Inductance LR circuits Maxwell’s Equations! We have demonstrated that a magnetic field can be produced by either a moving charged particle, currents or by a time dependent electric field. Now we will see that an ELECTRIC field can be produced by a time dependent magnetic flux!

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Chapter 30: Faraday’s Law o What is magnetic flux? o How can magnetic flux change? o What happens if the magnetic flux through a circuit changes? o What is Faraday’s Law ? o How do you determine the direction of emf produced by changing flux? o How does Faraday’s Law enable power generation?
Magnet and Coil Demo: What do we notice? Magnet and Coil Demo: What do we notice? When the magnet is stationary relative to the coil there is no current through the coil. When the magnet is moved towards the coil or moved away from the coil, A CURRENT FLOWS THROUGH COIL EVEN A CURRENT FLOWS THROUGH COIL EVEN THOUGH THE COIL IS NOT ATTACHED TO ANY THOUGH THE COIL IS NOT ATTACHED TO ANY BATTERY OR POWER SUPPLY?!! BATTERY OR POWER SUPPLY?!! When the north pole of magnet inserted, the current through the coil is in the clockwise direction. When the north pole of the magnet is removed, the current flows in the counter clockwise direction. Michael Faraday and Joseph Henry in the early 1800’s developed an understanding of how changing magnetic fields can produce electric fields.

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Two Coils Demo- what do we notice? Two Coils Demo- what do we notice? If we put an DC voltage, independent of time, on the coil 1, the light does not light up, even though we measure a magnetic field. If we put an AC voltage, time alternating, across coil 1 and put coil 2 on top, the light bulb lights up, EVEN THOUGH THERE IS NO EMF SOURCE FOR COIL 2?!! If we make move coil 2 to reduce the area of overlap of the two coils, the light dims. If we move coil 2 so it is perpendicular to coil 1, the light turns off, no current in coil 2.
What do these demos suggest? What do these demos suggest? When the magnetic field flux flux through a conducting loop is changing in time, there is an EMF FARADAY’S LAW FARADAY’S LAW How can the magnetic flux through a conducting loop change in time? C time dependent magnetic field . Example: Switching on/off solenoid current. C time dependent surface area defined by loop. Example: Loop moving relative to field C time dependent surface normal relative to the field direction . Example: Rotating loop between magnetic poles B d d mf B dA dt dt Φ ε = - = - ur ur

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In fig.(a) we change B with time as we approach the bar magnet closer to the wire loop. In fig.(d) we we change the
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## This note was uploaded on 10/10/2010 for the course PHY 108 taught by Professor Iashvili during the Spring '08 term at SUNY Buffalo.

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PHY108 Chapter 30 - Ch 30 Faradays Law We have demonstrated that a magnetic field can be produced by either a moving charged particle currents or

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