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

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Homework Help Overview

The discussion revolves around an electromagnetic induction problem involving a magnet moving through a coil and the resulting induced emf over time. Participants are analyzing the relationship between the magnetic field and the induced emf as the magnet enters and exits the coil.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to describe the behavior of induced emf based on the magnetic field's changes as the magnet moves through the coil. Some participants question the measurement points for emf and the vector nature of the magnetic field.

Discussion Status

Participants are actively exploring different interpretations of the problem. Some guidance has been offered regarding the relationship between the magnetic field direction and the induced emf, but no consensus has been reached on the original poster's reasoning.

Contextual Notes

There is a noted discrepancy between the original poster's understanding and the textbook answer regarding the sign of the induced emf. The discussion includes considerations of vector relationships in the context of magnetic flux.

chound
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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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