# Homework Help: Metal rod rotating in magnetic induction.

1. Feb 21, 2013

### amk_dbz

1. The problem statement, all variables and given/known data
A metal rod (1/sqrt(pi)) m long rotates about one of its ends in a plane perpendicular to magnetic induction of 5*10^-3 T. Calculate the number of revolutions made by the rod if EMF induced between the ends of the rod is 1.5 mV.

I have been thinking about this problem for a long time but in vain. I just don't understand where to start.Any help will be appreciated.
Thanks

2. Relevant equations
Faraday's law : EMF induced=- d∅/dt

3. The attempt at a solution
I have tried using Faraday's law but can't figure out equation for ∅. I just don't understand where to start.Any help will be appreciated.
Thanks

2. Feb 21, 2013

### rl.bhat

Consider a small element dx of the rod at a distance x from the fix end. Suppose it is moving with a velocity v in the circular orbit.
Then the induced emf in this element dε = -vBdx. Put v = ωx.
To find the total induced emf, find the integration from zero to the given length of the rod.
In the problem emf is given. Find ω, which gives you the number of rotation per second.

3. Feb 21, 2013