Electric field in a ring between two magnets

[critter]

Homework Statement

A metal ring 4.50cm in diameter is placed between the north and south poles of large magnets with the plane of its area perpendicular to the magnetic field. These magnets initially produce a magnetic field of 1.12T, but are gradually pulled apart, causing the field to remain uniform, but decrease at a rate of 0.250T/s. What is the magnetic field induced in the ring?

Homework Equations

See attachment, I wasn't sure how to put some of the symbols in here.

The Attempt at a Solution

I am not sure how to approach it since there is no velocity given. If I could somehow relate the change in the B field to velocity, I think I could solve it. Here is the equation for B:
B=1.12-0.25t
dB/dt=-0.25T
How can I use that in my solution?

 

[gomboc]

Are you sure the question isn't asking for the EMF induced in the ring, rather than the magnetic field? Induced magnetic field doesn't make any sense.

In that case, you know the rate of change of the magnetic field dB/dt. Multiply that by the loop's area, and you have the rate of change of magnetic flux $$d\phi /dt$$, which is equal to the induced EMF.