Electro magnetic Induction problem. Simple one, but check wehre I am wrong.

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SUMMARY

The discussion centers on a problem involving electromagnetic induction, specifically the induced electromotive force (emf) in a coil as a magnet moves through it. The participant initially misinterprets the sign of the induced emf, stating it becomes negative as the magnetic field (B) increases. However, upon further analysis, it is clarified that the magnetic field and area vectors are antiparallel initially, resulting in a positive induced emf. The correct interpretation is that the emf first appears positive as the magnet enters the coil, forming a V shape in the graph of emf versus time.

PREREQUISITES
  • Understanding of electromagnetic induction principles
  • Familiarity with Faraday's Law of Induction
  • Knowledge of vector analysis in physics
  • Ability to interpret graphical representations of physical phenomena
NEXT STEPS
  • Study Faraday's Law of Induction in detail
  • Learn about the relationship between magnetic flux and induced emf
  • Explore vector analysis in electromagnetic contexts
  • Practice plotting graphs of induced emf with varying magnetic field scenarios
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Students of physics, educators teaching electromagnetic theory, and anyone interested in understanding the principles of electromagnetic induction and its applications.

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Electro magnetic Induction problem. Simple one, but please check wehre I am wrong.

Homework Statement



A magnet moving down, goes through a coil and exits it below. Plot the graph showing variation of induced emf in coil with time.

Homework Equations



emf = - Flux/Time

The Attempt at a Solution


As the magnetic field B increases, emf becomes more and more negative.
Then while leaving, B decreases, emf becomes more and more positive.

Hence

The emf is first negative, forms a V shape in the negative emf region and then an inverted V in the positive emf region when it leaves.

4.Answer in the textbook
The emf is first positive ... in other words just the opposite of what I said.

Where did I go wrong ?
 
Physics news on Phys.org
From what two points are you measuring the emf?
 
From either ends of the coil
 
Isn't the "B" in this system a vector?

(Those tricky vectors...)

:cool:

~A137
 
Ya. But how will that matter?
 
I think I get it now.
Initially B and Area vectors are antiparallel, so flux is negative. Hence, the induced emf is positive.
 

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