# Determine Average Voltage

1. Mar 22, 2009

### wayneinsane

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

There is uniform magnetic field of 25 mT into paper in a region.
Where there is kink in a wire..

The initial diameter of the kink is 2 cm. The wire is pulled out and kink shrinks to dosimeter = 0 in 50 ms.

(i) Determine the average voltage between A and B. and the polarity of A and B.

(ii) Suppose the kink is undisturbed and the magnetic field increases to 100 mT in 4 x 10-3 s, then determine the average voltage between A and B and the polarity of A and B.

2. Relevant equations

magnetic flux = BAcos(theta)

emf = -N magnetic flux / delta T

3. The attempt at a solution

for (i), I did magnetic flux = BAcos(theta)... B = 2.5x10^-2 T, A = 3.14x10^-4, and cos theta = 1... so mag flux = 7.85x10^-6...so plug that into emf and you get 7.85x10^-6/50x10^-3s and you get 1.57x10^-4V....is this correct??

for (ii) i did change in flux so Bf x A - Bi x A which is 5.14x10^-5 T - 7.85 x 10^-6 T which gives 2.355 x 10^-5T.... you plug that into EMF equation and get 2.355x10^-5T/4x10^-3s which equals 5.89x10^-3V...is this correct??