# Homework Help: Grade 12 Physics - Equations relating current and radius of a beam

1. Oct 18, 2011

### GR + QM

1. The problem statement, all variables and given/known data
Okay, the assignment involves electron beams of various voltages, currents, and radii
Basically, the situation is, several of these beams were measured for the aforesaid values.
The values as follow are in the following order - Voltage (J/c) - Current in Helmholtz Coils (A) - Diameter of Electron Beam (cm)

1. 42.5 - 2.30 - 6.0
2. 44.0 - 1.90 - 7.5
3. 45.0 - 1.70 - 8.7
4. 46.0 - 1.40 - 10.3
5. 46.5 - 1.20 - 12.0
6. 47.0 - 1.15 - 12.5

With the following values, I'm told to graph the relationship between the current and the radius, and to graph the relationship between voltage and radius.

I have done that, BUT, the problem is that I'm not supposed to guess a line of best fit, but I'm supposed to formulate equations showing what the line must look like. This is what gets me.

I'm quite lost because afterwards, I have to make a THIRD graph showing the straight line relationship between voltage and radius.

2. Relevant equations
All equations relevant to magnetic fields and electrons, such as
F$_{}m$= qvB

All equations here are allowed to be used http://education.alberta.ca/media/3091847/01 p30-3797_ft_databooklet-2011.pdf

3. The attempt at a solution

I've graphed the first two given graphs, I plotted the dots but now I cannot proceed because I can't figure out an equation relating the radius and current.

Thank you in advance for all supportive and productive comments, the help is greatly appreciated. I am excelling at the moment, but this has stumped me and I've spent hours with no avail.

2. Oct 18, 2011

### GR + QM

Never mind! I got it all, the lab was supposed to end up with finding the charge : mass ratio of an electron, and I got it all.