# Magnetic Field from a Graph?

1. Mar 9, 2007

### candyq27

1. The problem statement, all variables and given/known data
I have a graph of an emf of a generator vs time, and i know the cross-sectional area per turn is 0.03m^2 and there are 160 turns. From the wave graph I figured out the frequency of the generator is 2.4Hz and the angular speed is 14.96rad/s. I need to figure out the magnetic field.

2. Relevant equations
e=-NAcos0B/t

3. The attempt at a solution

I found the frequency and angular speed from the graph but I have no idea how to find the magnetic field from a graph. Please help. Thank you.

2. Mar 10, 2007

### dobry_den

It's important to realise that the emf is directly proportional to the change of magnetic flux:

$$\Phi = BS\cos{\omega}t$$

$$emf = -N \frac{d\Phi}{dt}$$,

that is:

$$emf = -NBS \frac{d}{dt}\cos{\omega}t = -NBS\omega\sin{\omega}t$$

Then rearrange it to get the formula for B.

Last edited: Mar 10, 2007
3. Mar 10, 2007

### candyq27

Ok so I rearranged the formula to get B=emf/-NAwsinwt
= 28/(-160)(.03)(14.96)(sin(14.96*.315))
=28/71.808
=0.38993
Is that correct? Thanks!