# Homework Help: Magnetron Electron Field Strength

1. Oct 19, 2008

### haxxorboi

1. The problem statement, all variables and given/known data
Suppose the resonant frequency is f = 1.47×1010 s−1; that is, the electron period of revolution is T = 6.80×10-11 s. What is the corresponding strength of the magnetic field?

2. Relevant equations
qvb=mv2/r
qb=mv/r

3. The attempt at a solution
1.6E-19*b=9.1E-31*v/r

I understand the general idea, to figure out b, but I don't understand how to figure out Velocity or Radius from the frequency/period.

Can someone give me a point in the right direction?

2. Oct 20, 2008

### alphysicist

Hi haxxorboi,

When they give the period, that is the period of what? In other words, if the period is 6.80×10-11 s, what happens every 6.80×10-11 seconds? Once you answer that, you should be able to write down an equation relating T, r, and v. What do you get?

3. Oct 20, 2008

### haxxorboi

Velocity=Distance/Time
Velocity=Circumference/Period
Velocity=2*Pi*R/6.8E-11 sec
Velocity=9.24E10R

1.6E-19*B=9.1E-31*(9.24E10R)/R

B=.5253 T

Thank you very much, that was killing me!