# Motional emf i think . change in area and magnetic field

1. Oct 29, 2008

### goWlfpack

motional emf i think..... change in area and magnetic field

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

A rectangular loop is located in a uniform magnetic field of magnitude 0.29 T directed perpendicular to the plane of the coil. If the area of the coil increases at the rate of 5.2 10-3 m2/s, what is the magnitude of the emf induced in the coil?

2. Relevant equations

ummmm maybe emf=blv
emf=-L (I/t)

3. The attempt at a solution

honestly i don't even understand conceptually what is going on in this problem so it is hard for me to find any equation(s) to help me solve it. The area of the coil decreases? that doesnt make sense to me and i have no idea what correlation that has to magnetic field other then flux=BA.... so help?

2. Oct 29, 2008

### Staff: Mentor

Re: motional emf i think..... change in area and magnetic field

Faraday's law relates EMF to the rate of change of the flux. (See: Faraday's Law.) What's the rate of change of the flux?

3. Oct 29, 2008

### goWlfpack

Re: motional emf i think..... change in area and magnetic field

Well the change in magnetic flux would be flux=B(deltaA)

so the change in flux should equal .001508

then faraday's law is emf=-N (change in flux)/change in time

but there arent any turns in this wire and also there is no time given. but if you put in 1 for each you get the change in flux which got a red x...ugh

4. Oct 29, 2008

### Staff: Mentor

Re: motional emf i think..... change in area and magnetic field

Try this:

Flux = BA, but B is fixed so only A changes.

Δ(Flux)/Δt = Δ(BA)/Δt = B ΔA/Δt

5. Oct 29, 2008

### goWlfpack

Re: motional emf i think..... change in area and magnetic field

ok so that gives me the change in flux. But how do i go about getting the emf without having a value for "N" or the number of turns?

6. Oct 29, 2008

### Staff: Mentor

Re: motional emf i think..... change in area and magnetic field

It's a single loop--so what do you think N is?