Magnitude of the non-coulomb electric field around a solenoid.

[Pepjag]

Homework Statement

A metal ring of radius r = 24 cm surrounds a
solenoid of radius R = 2 cm and 10000 turns.
The magnetic field inside the solenoid changes from 5 T to 3 T in
0.1 s. Find the magnitude of the non-Coulomb
electric field along the ring.
Answer in units of V/m

Homework Equations

emf = -N*d(flux)/dt = -N*db/dt*A
emf = integral of E*dl

The Attempt at a Solution

Ok, so i pretty much just plugged in numbers. for the emf:

emf = -10000*(3-5)/0.1*pi*0.02^2 = 251.3 volts.

For the electric field:

E = emf/L = 251.3/2*pi*0.24 = 166.7 V/m

Unfortunately, the computer keeps saying I'm wrong. Am I really doing something wrong? This seemed pretty straight forward.

 

[aralbrec]

Ok, so i pretty much just plugged in numbers. for the emf:

emf = -10000*(3-5)/0.1*pi*0.02^2 = 251.3 volts.

Am I really doing something wrong?

You're looking at the emf induced in the metal ring. How many turns of wire does a metal ring have?

 

[Pepjag]

Wait, so you have to use the emf equation from the ring's perspective?

emf = (3-5)/0.1*pi*0.24^2 = 3.62 volts.

E = emf/L = 251.3/2*pi*0.24 = 2.40 V/m

Or do I still use the solenoid's area for the emf?

 

[Pepjag]

I have until 11:30 ct to finish this one problem, can anyone please give input.