# Homework Help: Electrons in a beam of televison tube

1. Mar 18, 2005

### Gonger

Ive got a question where I have to find the acceleration of a single electron due to the magnetic field. Now here is what I did. I tired to find Velocity using KE = .5mv^2. Solving for v. Then knowing that F=qvB and F=ma I made the equation qvb/m=a. But I cant get this to work. Is there some thing that I'm doing wrong. This is a related question with the numbers in it:
I think my problem is with converting uT to T for the electric field. And converting my 24 keV to J. Anyone have some help. Thanks.

2. Mar 18, 2005

### Andrew Mason

Your approach is correct except that the force is:

$$\vec F = q\vec v \times \vec B = qvBsin\theta$$

What is the angle of $\vec v$ to the magnetic field?$\vec B$ Why not show us what you have done? It is a little hard to figure out where you may have gone wrong otherwise.

AM

3. Mar 18, 2005

### witze

Well, the vertical component of B was given in the problem, so I don't think you need to do the cross product. You're probably just having problems with unit converstions.

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