# Circulating Charged Particle

1. Oct 20, 2009

### exitwound

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

An electron of kinetic energy 1.20keV circles in a plane perpendicular to a uniform magnetic field. The orbit radius is 25.0cm. Find a.) The electron's speed. b.) the magnetic field magnitude c.)the circling frequency, and d) the period of the motion.

2. Relevant equations

$$F=m\frac{v^2}{r}$$
$$qvB=m\frac{v^2}{r}$$
$$r= \frac{mv}{qB}$$
$$T=\frac {2\pi r}{v}$$

3. The attempt at a solution

1.2 keV = 1.92 x10^-16 Joules

I don't know what to do to find the velocity. I know if it's moving, it's kinetic energy can be linked to the velocity somehow. It's acceleration is v^2/r but that's all I know.

Anyone?

2. Oct 20, 2009

### thaer_dude

k=0.5mv2

you should know that formula

3. Oct 20, 2009

### exitwound

That's what I did FIVE TIMES and kept getting the wrong answer. I do it NOW after you've responded and it's correct. I was absolutely sure that .5mv^2 was the right formula to use. I don't know what I was doing wrong.

$1.92x10^{-16}=.5(9.1x10^{-31})(v^2)$

$v^2=\frac{(1.92x10^{-16})(2)}{(9.1x10^{-31})}$
$v=2.05x10^7$

sorry to bug you.

4. Oct 20, 2009

oh well :p