# Resistance in emf - Faraday's Law

1. Apr 1, 2012

### tnbstudent

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

A rectangular wire loop measures 5.00 cm by 8.00 cm, and lies in the plane of the page. It has a resistance of 3.00 Ω. In this region, there exists a uniform magnetic field pointing into the page. Its magnitude, in Tesla, varies according to the equation B(t) = 10.0 − 0.300t2. (a) Calculate the magnitude of the magnetic flux through the loop at t = 2.50 s. (b) How much current is flowing in the loop at t = 2.50 s?

2. Relevant equations

ε=dF/dt (F=flux)
B=μ*B*n

3. The attempt at a solution
I thought that a seemed simple... I guess I was wrong.
Since B(t)=10-0.3t^2 I took the derivative of B with respect to t
dB/dt=-0.6t
for t=2.5 seconds
B't = 1.5T
Using ε=dF/dt (F=flux)
ε=A*(dB/dt)*cosθ
ε=(0.05m)*(0.08m)*(1.5T) = .006Tm^2
But, the answer is 0.0325Tm^2
I haven't used the resistance given in the problem and I'm not quite sure where it goes.

for part b I was thinking of using
B=μ*I/2πr
but, again I haven't used resistance and I'm not sure what I would use for r (distance)??