Magnetic Flux & Current in a Dropped Magnet & Wire Loop

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SUMMARY

The discussion centers on the behavior of induced current in a wire loop when a bar magnet is dropped above it, specifically analyzing the effects of Lenz's Law and Faraday's Law. As the south end of the magnet approaches the loop, the induced current flows counterclockwise. Once the magnet passes through the loop and begins to move away, the current reverses and flows clockwise. The key takeaway is that the direction of the induced current is determined by the change in magnetic flux, not the magnetic flux itself.

PREREQUISITES
  • Understanding of Lenz's Law
  • Familiarity with Faraday's Law of Electromagnetic Induction
  • Basic knowledge of magnetic fields and flux
  • Concept of induced electromotive force (emf)
NEXT STEPS
  • Study the applications of Lenz's Law in electromagnetic systems
  • Explore advanced concepts in Faraday's Law, including practical experiments
  • Investigate the relationship between magnetic flux and induced current in various configurations
  • Learn about the effects of different magnet orientations on induced currents
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Students of physics, educators teaching electromagnetism, and anyone interested in understanding the principles of electromagnetic induction and their applications in real-world scenarios.

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Homework Statement


A bar magnet is held above the center of a wire loop lying in the horizontal plane, as shown in the figure below. The south end of the magnet is toward the loop. After the magnet is dropped, what is true of the current in the resistor as viewed from above? (Select all that apply.)
20-mc-figure-11.gif

It is counterclockwise as the magnet falls toward the loop.
It is clockwise as the magnet falls toward the loop.
It is always clockwise.
It is clockwise after the magnet has moved through the loop and moves away from it.
It is first counterclockwise as the magnet approaches the loop and then clockwise after it has passed through the loop.

Homework Equations


Lenz's law and Faraday's Law

The Attempt at a Solution


This is my conceptual picture of what's going on.

Untitled.png

As the magnet is falling in the field lines are going N to S as always. So Just at the moment when the bottom of the South pole of the magnets hits the area inside the circle the field lines are coming toward us (as viewed from the top). As the magnet falls through and the N side is facing us, the field lines are again, coming toward us.
In both cases the current will be induced in such a way that the magnetic flux through the surface is constant. So it seems to me that it should flow clockwise in both cases. This is, however, incorrect. Where am I going wrong?
 
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The induced emf is proportional to the change in (i.e., time derivative of) the magnetic flux, not to the magnetic flux itself.
 
Yes, that is what my pictures are trying to illustrate.
 
So how is the flux changing when the magnet falls into the loop? How is it changing when it falls out of the loop?
 

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