# Homework Help: Induced emf in a square loop

1. Jul 7, 2007

### supersunshine

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

"A square loop of wire is held in a uniform magnetic field of .24 T directed perpendicular to the plane of the loop. The length of each side of the square is decreasing at a constant ratee of 5.0 cm/s. What is the emf induced in the loop when the length 12 cm?

2. Relevant equations

EMF= -d(flux)/dt = B . d(area)

3. The attempt at a solution

I think once the rate of change for the area is determined you can multiply it by the magnetic field. however, im confused about determining the change in flux from the given variables. Is there going to be flux on each side of the square or only on certain sides? for dA can you mu ltiply the rate of change of the side by the length of a side and square that value?

thanks

2. Jul 7, 2007

### nrqed

I am not sure what you mean by this. You care only about the flux through the surface enclosed by th eloop
$A = L^2$. So what is $\frac{dA}{dt}$?