# Speed of an Electron and the Magnetic field

1. Apr 20, 2009

### mlsohani

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

An electron with kinetic energy 1.60 keV circles in a plane perpendicular to a uniform magnetic field. The orbit radius is 24.0 cm.
a Find the speed of the electron.
b Find the Magnetic Field

2. Relevant equations

k=1/(2mv^2)
B=mvqr

3. The attempt at a solution
I first converted keV to Joules which came out to be 2.5635 e-16 J

I then made the equation to solve for v : v=sqrt(1/2mk)

But I came out with the velocity being e22 4.627 km/s which is not right

2. Apr 20, 2009

### alphysicist

Hi mlshani,

This equation does not look right to me; do you see what it needs to be?

3. Apr 20, 2009

### mlsohani

No I thought that was the equation, at least that is the one on my physics book?
Is there another equation to find the speed of an electron?

4. Apr 20, 2009

### Volcano

(mV^2)/2

5. Apr 20, 2009

### mlsohani

Thank you!

I can't believe I saw that equation as having everything in the denominator!

Thank you!