Magnetic Field and Centripetal Force

Thread Starter


Joined Jul 12, 2011
Hi all,

I've got a pretty quick question about magnetism.

A magnetic field, of 0.6 T, going into the paper, causes a charged particle to move in a horizontal circle. The particle has mass 1.67 x 10^-27 kg and charge 1.6 x 10^-19 C.

A. How long does it take for the particle to go once around the circle?

B. How many times per second does the particle go around the circle?

Relevant Equations: qvB = (mv^2)/R F = qvBsin(θ) Time = Distance/Velocity

I feel like there is a piece of information missing from this problem, I can't seem to solve it with any of the above equations. We don't know the velocity or radius of the circle so that rules the first equation out. We also don't know the magnitude of the magnetic force so that rules the second equation out.

Help is much appreciated.


Joined Feb 5, 2010
That is correct, since the particle has MASS, it cannot be moving at light speed, but must be traveling at some speed less than 'c'. The magnetic field strength IS GIVEN. They do also, give the charge on the particle, which I believe can be used to calculate particle velocity, in response to the magnetic field it encounters. Do some google searches with those keywords.

Thread Starter


Joined Jul 12, 2011
I was just looking at that page! Haha. Unfortunately I don't think this helps me as the equation the proved was already known to me. Again, I don't think we have enough information in the problem because we have TWO unknowns and ONE equation.


Joined Jul 7, 2009
The answer was already given to you by virtue of Kermit2's link. Hint: this characteristic is important in the operation of a cyclotron. I suggest you go back and read that page, as you'll learn some interesting tidbits.