# Period of an Electron Around a Magnetic Field

## Homework Statement

An electron enters a uniform magnetic field of 0.152 teslas such that the electron follows a circular path. What is the period of the electron's motion? Electrons have a mass of about 9.11 x 10-31 kilograms each. Hint: Since the radius of the electron's path is not given, it must cancel out of the equations.

Fm = Q * V * B

F = M * A

A = V^2/r

V= 2(pi)r/T

## The Attempt at a Solution

Q * V * B = M * A
Q * V * B = M * V^2/r
Q * 2(pi)r/T * B = M* V^2/r
Q * 2(pi)/T * B = M * V^2
(1.6E-19) * 2(pi)/T = (9.11E-31) * (3.00E8)^2
Solve for T
T = 1.86E-6 s
But it is wrong...

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ideasrule
Homework Helper
How can you use v=3.00E8? Electrons can't possibly travel at the speed of light, and even if they could, the question doesn't say that they do.

Try substituting 2(pi)r/T in the v on the right side as well. Better yet, cancel out one v in Q * V * B = M * V^2/r, then substitute 2pi*r/T into the remaining v.

Cool got it... here is what I did if somebody else would like to see...

Q * V * B = m * v^2/r

Q * B = M * V / R

Q* B = M * (2(pi)r/T)/r

Q * B = M * (2pi)/T

T = 2(pi) * M / Q * B

I got 2.35E-10 seconds... worked great... thanks