# Homework Help: Calculating E/M for Helmholtz Coils -- help please

1. Oct 23, 2014

### grandpa2390

edit: wait... I think the discrepancy is that I calculated Coulombs per kg? and the accepted value I was looking at was in abcoulombs per kg. If that is indeed the case, then my answer is indeed close to the accepted value of 1.76 * 10^11 Coulomb/kg.

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

I am trying to calculate e/m for data I got from a laboratory experiment with a helmholtz coils. I am not sure if I have bad data, or if I have a mistaken unit somewheres. I am getting 1.96 * 1011 after I average all my e/m together. I should be getting 1.76 * 107

Am I doing something wrong, or is it my data? I am not going to put all my data up. I will just put some 1 measurement and please tell me if I am using wrong units somewheres.

2. Relevant equations

3. The attempt at a solution

my measurement is:

accelerated voltage = 40 volts
current for helmholtz coils = 2.46 Amps
Radius of coil = .33 meters
there are 72 turns on each coil
radius of the electron beam = .039 meters

I get 2.25 * 10^11
is this what my data gives me, or am I using the formula incorrectly? I should get 10^7

Last edited by a moderator: May 7, 2017
2. Oct 28, 2014