Lenz's Law: Direction of Flux & Current

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SUMMARY

The discussion centers on Lenz's Law and its application to a solenoid placed in a vertical magnetic field. When the magnetic field is suddenly switched off, a current is induced in the solenoid, which flows counter-clockwise to oppose the change in magnetic flux. This phenomenon is explained through the principles of electromagnetic induction, specifically how the induced current generates a magnetic field that counters the initial field. The participants clarify that the induced current arises from the solenoid's internal structure, as it seeks to maintain the original magnetic flux direction.

PREREQUISITES
  • Understanding of Lenz's Law and its implications in electromagnetism
  • Familiarity with electromagnetic induction principles
  • Knowledge of solenoid construction and behavior in magnetic fields
  • Basic concepts of magnetic flux and its measurement
NEXT STEPS
  • Study the mathematical formulation of Lenz's Law in electromagnetic theory
  • Explore Faraday's Law of electromagnetic induction for deeper insights
  • Investigate applications of Lenz's Law in electrical engineering and circuit design
  • Learn about the behavior of inductors in AC circuits and their role in energy storage
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Students of physics, electrical engineers, and educators seeking to deepen their understanding of electromagnetic principles, particularly in relation to solenoids and magnetic fields.

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Homework Statement



I don't have the question with me, it was on a test I did. It was something like this though:

A coil is placed vertically on a table. The magnetic field there is also vertical. If the magnetic field is suddenly switched off, in which direction would the current in the solenoid move?

A) Clockwise
B) Counter-clockwise
C) There would be no current
-and I forgot the rest of the choices.

The Attempt at a Solution



Well it would look something like this:

http://img43.imageshack.us/img43/2058/emfb.jpg

So, current is produced when there is a change in the magnetic field, so there is obviously would be current if the field is turned off. And that current's field would try to counter the flux.

But some things aren't clear to me;

1) Since the field is even on all points of the solenoid, which side of the solenoid (inner or outer) would be the one that creates the "counter-"magnetic field against the flux? Would the field be countered from within or from the outside?

2) Which direction would the flux be (that creates the current) if the "field is suddenly switched off"?
 
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Your current would be counterclockwise. Lenz's Law states that this coil will attempt to fight the change in flux that is brought about when the B field is switched off. Since that original B field was pointed up, the current must be CCW to produce a B field in that same direction in an attempt "to fight" the change in flux from some flux to zero.
 

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