Rate of current changing through an inductor

[supersunshine]

Homework Statement

At time t=0 a 45V potential difference is applied to the leads of a coil with inductance L=50 mH and resistance R=180 ohm. At what rate is the current through the coil increasing at t=1.2ms?

Homework Equations

1) L=EMF/ (di/dt)
2) L=N(flux)/i
3)emf=iR

The Attempt at a Solution

I thougt you could first find the current at t=o using EMF=iR= .25 A, then you could find the current at t=1.2 ms, by first finding the flux at this time to do this:

I thought -d(flux)/dt=EMF= 45V. Is it correct to say that the magnetic flux is changing at a rate of 45 wb/s ? and then multiply by time and use equation 2 , however we don't know the number of turns, which is where I am stuck

any hints would be appreciated

 

[Astronuc]

This is a simple RL circuit.

http://farside.ph.utexas.edu/teaching/302l/lectures/node88.html