# Induced emf

1. Jan 29, 2006

### Pixter

If we have a loop with radius 12 cm that lies in a uniform magnetic field of 1.5T.

The magnetic field is in the positive z direction and the loop lies in the horizontal xy-plane. Now if the loop is removed from the field in a time interval of 2.0x10^-3 s what will the average induced emf be.

Right now first I thaught it might be zero but then seeing as the b field will be constant and A will change.

therefore it has to be emf= - -b x dA/dt

but how can i describe the rate of change of A?

ps:am I even on the right track? =)

Last edited: Jan 29, 2006
2. Jan 29, 2006

### PPonte

If I understood well the magnetic field is perpendicular to the loop:
the A will decrease from it's maximum value (the area of the loop: 4,52 x 10^-2 m^2) to zero.

3. Jan 29, 2006

### Pixter

yeah so the average emf induced would be d(A/2)/dt ?

4. Jan 29, 2006

### PPonte

In my opinion, we could simplify the formula:
emf induced = B.A/dt

B= 1,5 T
A (of the loop) = 4,52 x 10^-2 m^2
dt = 2,0 x 10^-3 s
emf = 33,9 V

But wait for the experts, it's possible that I am mistaken.

Last edited by a moderator: Jan 29, 2006
5. Jan 29, 2006

### Psi-String

I thinks it is

$$\frac{\Delta \Phi_B}{\Delta t}$$

since it asks average value not instantanious one, I think 33.912 V is a correct answer.

6. Jan 29, 2006

### Pixter

but surely the average A confined in the magentic field during dt must be half A.. therefore the average Induced emf must be -d(A/2)/dt

or?

7. Jan 29, 2006

### PPonte

It is not an average A but a variation of A.
Phi=B.A.costheta

and

efm = dPHi/dt

PS- Sorry, but I don't know to latex.

Last edited by a moderator: Jan 29, 2006