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

by chound
Tags: check, electro, induction, magnetic, simple, wehre
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chound
#1
Feb26-07, 12:18 AM
P: 239
1. The problem statement, all variables and given/known data

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

2. Relevant equations

emf = - Flux/Time

3. 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 ?
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dimensionless
#2
Feb26-07, 09:47 AM
P: 464
From what two points are you measuring the emf?
chound
#3
Feb26-07, 10:26 PM
P: 239
From either ends of the coil

Axiom_137
#4
Feb27-07, 01:17 AM
P: 7
Electro magnetic Induction problem. Simple one, but check wehre I am wrong.

Isn't the "B" in this system a vector?

(Those tricky vectors...)



~A137
chound
#5
Feb27-07, 02:13 AM
P: 239
Ya. But how will that matter?
chound
#6
Feb27-07, 02:32 AM
P: 239
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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