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Lenzs Law

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Minus Sign There is a minus sign in Faradays Law. There is a minus sign in Faradays Law. Relates flux change to polarity of emfRelates flux change to polarity of emf Lenzs Law restates this connection. Lenzs Law restates this connection. The induced emf will produce a current that acts to oppose the change in magnetic field.

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Opposing Change As the magnetic flux increases the current increases. As the magnetic flux increases the current increases. The current creates a magnetic field in an opposite direction to the increasing external field. The current creates a magnetic field in an opposite direction to the increasing external field. As the field decreases the induced current creates a field that replaces the lost field. As the field decreases the induced current creates a field that replaces the lost field.

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Squashed Coil A looped coil has 200 turns, resistance of 5 and an area of 0.25 m 2. A looped coil has 200 turns, resistance of 5 and an area of 0.25 m 2. It is in a 0.40 T downward field and is squashed to zero area in 100 ms. It is in a 0.40 T downward field and is squashed to zero area in 100 ms. What happens to the current? What happens to the current? The flux is reduced by the shrunk area. The flux is reduced by the shrunk area. = -.100 T m 2 The current will flow to create a replacing magnetic field. The current will flow to create a replacing magnetic field. The current will flow counterclockwise seen from above. The current will flow counterclockwise seen from above.

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Maglev Magnetic levitation uses opposing magnetic fields. Magnetic levitation uses opposing magnetic fields. Current in the track sets up a field to oppose moving magnets in the train. Current in the track sets up a field to oppose moving magnets in the train. The force can lift the entire train off the ground. The force can lift the entire train off the ground.

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Eddy Currents next A solid metal plate is affected by Lenzs Law. A solid metal plate is affected by Lenzs Law. A current can move through the metal. A current can move through the metal. Eddy currents will circulate to oppose the change in field. The motion can also slow to resist the change. The motion can also slow to resist the change.

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Copyright © 2009 Pearson Education, Inc. Chapter 31: Faraday’s Law.

Copyright © 2009 Pearson Education, Inc. Chapter 31: Faraday’s Law.

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