# Homework Help: What is the value of the B field in Teslas, inside the Helmholz coils?

1. Oct 19, 2014

### Eddie10

1. The problem statement, all variables and given/known data
For a current of 2.5 amps, what is the value of teh B field in Teslas, inside the Helmholz coils in the e/m apparatus?

2. Relevant equations

B = 7.7 x 10^4 x I , I is the current in amps.
3. The attempt at a solution
B = B = 7.7 x 10^4 x 2.5 amps = .001925 = 1.925 x 10^-3

Did I do this correctly? This is for the E/M Experiment.

2. Oct 19, 2014

### Staff: Mentor

It's impossible to say whether your result is correct, without knowing the radius of the coils and the number of turns of wire in each coil. You can see the complete formula here:

http://en.wikipedia.org/wiki/Helmholtz_coil

3. Oct 19, 2014

### Eddie10

Hmmm...I don't have any of that information for this problem, and it was not given as part of the lab.

The reason I don't have this information is because I have not conducted any type of experimental data collection, as I am fulfilling a pre-lab questionnaire for credit.

Would it even be possible to say that I am, generally, in the right track with my answer?

Last edited: Oct 19, 2014
4. Oct 20, 2014

### Staff: Mentor

When you plug the radius, number of turns, and $\mu_0$ into the formula on the Wiki page, you get a constant times I. Apparently they pre-calculated the constant for you, so you just have to trust that they got it right. You wrote the exponent as 4, but the result of your calculation indicates that you used -4, which is more likely to be correct than +4. Even 1.0 Tesla is much larger than you're likely to produce in an introductory physics lab. The world record appears to be about 90 Tesla.

(When I taught labs that used Helmholtz coils, I told my students the number of turns, and asked them to measure R for themselves and calculate B using the Wiki formula. You guys have it easy. )