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

  • Thread starter chound
  • Start date
  • #1
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Electro magnetic Induction problem. Simple one, but plz 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 ?
 

Answers and Replies

  • #2
From what two points are you measuring the emf?
 
  • #3
158
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From either ends of the coil
 
  • #4
7
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Isn't the "B" in this system a vector?

(Those tricky vectors...)

:cool:

~A137
 
  • #5
158
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Ya. But how will that matter?
 
  • #6
158
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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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