Rate of Magnetic Field Change

1. Apr 10, 2010

ihearyourecho

1. The problem statement, all variables and given/known data

A single conducting loop of wire has an area of 7.2×10−2m2 and a resistance of 120 ohms. Perpendicular to the plane of the loop is a magnetic field of strength 0.50 T.

At what rate must this field change if the induced current in the loop is to be 0.39A?

2. Relevant equations

emf=(-NdeltaIB)/(deltat)
Rate of change = emf/-N

3. The attempt at a solution

emf=(-NdeltaIB)/(deltat)
Rate of change = emf/-N

It's a single loop, so N should be 1
Rate of change - emf/-1

emf=v=IR

Rate of change = -IR
Rate of change = -(.39A)*120ohms=-46.8

This isn't right though.

Thanks for the help :)

Last edited: Apr 10, 2010
2. Apr 11, 2010

ihearyourecho

anyone? :)

3. Apr 11, 2010

kuruman

The correct equation is

emf = - dΦ/dt

where Φ is the magnetic flux through the loop which you need to calculate first.

4. Apr 11, 2010

ihearyourecho

Arggh, I've been reading it as magnetic field, not flux. Thanks!