What Is the Correct Period and Frequency for an Electron in a Magnetic Field?

[BigFlorida]

Homework Statement

Find the period and frequency of the motion of an electron of kinetic energy, E, 34 KeV as is moves in a circular orbit perpendicular to a magnetic field, B, of 0.270 T.

Homework Equations

For speed, v:

For charge, q:

For mass, m:

For radius, R:

For frequency, f:

For period, T:

The Attempt at a Solution

We were told to treat this classically, so I computed the radius by solving for the speed with the classical kinetic energy formula,

, from which I found

, which gave me R = 2.2 mm, which is the correct radius. I then went on to use the relation

and this is where things went horribly wrong. I got the answer

, which seems very reasonable to me. I obtained

for the frequency, which also seems very reasonable to me. The only problem is, the answers are wrong or at least our homework website (WebAssign) says that those are the wrong answer. Anyone see a mistake I may be making?

 

[mfb]

Just a rounding issue? 7.56 GHz according to WolframAlpha.
Looks correct.