# Solving for a neutralizing B0 in a Thomson Cathode Ray (Algebra?)

## Homework Statement:

In your experiment, you measure a total deflection of 4.12 cm when an electric field of 1.10×103V/m is established between the plates (with no magnetic field present). When you add the magnetic field as described in Part C, to what value do you have to adjust its magnitude B0 to observe no deflection?

Assume that the plates are 6.00 cm long and that the distance between them and the screen is 12.0 cm.

## Relevant Equations:

deltaY = eE0d(d+2L)/2m(v0)^2

V0 = E0/B0
I've attached a picture from the problem, the given equations, and my work so far.

I knew I had a problem when My units wouldn't check out. This should just be simple algebra but It's not working. Please help me to understand what I am doing wrong.

#### Attachments

• 12.2 KB Views: 39
• 222 KB Views: 54

Related Introductory Physics Homework Help News on Phys.org
collinsmark
Homework Helper
Gold Member
I haven't gone through your whole attempted solution yet, but regarding your units,

$\mathrm{T = \frac{kg}{s \cdot C} = \frac{N \cdot s}{m \cdot C}}$

These are all the same units, equivalent to 1 Tesla. You've indicated near the end of your work that they are not the same, but they in fact are the same. If it helps, recall that

$\mathrm{N = \frac{kg \cdot m}{s^2}}$

This is unfortunate. I confirmed what you told me about the units but my answer is still wrong.

I have double checked the values they gave me, adjusted the resolution of my constants (eg. the charge and mass of the electron) and even tried changing signs. My answer makes sense to me but is apparently wrong. And the units agree with the setup being right so I believe it has to be my values

... I forgot to raise everything to the 1/2 power...... Well at least I learned something valuable about the units of magnetic field. I'll make sure to add that to my note cards. (Units are life)

Thank you for your help and have a good night.

collinsmark