# Unraveling coil inducing EMF

I have a homework problem where there is a long copper wire around a toilet paper roll that is placed in a uniform magnetic field. The axis of the roll is aligned with the field.
I am given the radius of the roll, strength of the field, and a velocity at which the wire is unrolled.
How do i calculate the magnitude of the EMF induced in the wire??

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quasar987
Homework Helper
Gold Member
How do you associate a speed to the unrolling?!? I don't understand.
Could you post the problem exactly as it it written please?

Btw - you posted in the wrong forum. Next time, please post in the appropriate sub-forum among those:

https://www.physicsforums.com/forumdisplay.php?f=152

Note that as it's said in Faraday's Law EMF is equal to d(N*magnetic_flux)/dt where N is a total amount of wire turns and magnetic_flux is per each one.

In your example your, magnetic_flux is const. and equal to BS=pi (r)^2 B. And only N changes in time. Try to think about dependence between N and time

Danger
Gold Member
What I have a lot of trouble understanding is... how do people with some sort of science education consistently misinterpret the sticky at the top of the forum that says 'Do not post your homework questions here.'? There are forums for that, but this is not one of them.