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

[chound]

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 ?

 

[dimensionless]

From what two points are you measuring the emf?

 

[chound]

From either ends of the coil

 

[Axiom_137]

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

(Those tricky vectors...)



~A137

 

[chound]

Ya. But how will that matter?

 

[chound]

I think I get it now.
Initially B and Area vectors are antiparallel, so flux is negative. Hence, the induced emf is positive.