1. The problem statement, all variables and given/known data An electron moving perpendicular to a magnetic field of 2.2*10^-2 T moves in a circle of certain radius. If the electron is moving with a speed of 1.5*10^7 m/s, what is the radius of the circle? 2. Relevant equations B field = u0*I / 2 pi r F = qvB 3. The attempt at a solution I'm confused about how to find the current I in order to solve for the radius. I know that F = (-1.9*10^-19)*(1.5*10^7)*(2.2*10^-2) = -6.27*10^-10 (but positive because magnitude), but I can't figure out how to solve for r with two unknowns (r and I). Can someone help? Thanks!