An alpha-particle is the nucleus of a helium atom; the orbiting electrons are missing. The alpha-particle contains two protons and two neutrons, and has a mass of 6.64x10^-27 kg. Suppose an alpha-particle is accelerated from rest through a potential difference and then enters a region where its velocity is perpendicular to a 0.0195 T magnetic field. With what angular speed w does the alpha-particle move on its circular path? B = 0.0195 T m = 6.64x10^-27 kg w = ? rad/s I did this: v = rw w = v/r r = mv/qB qB/m = v/r w = qB/m how ever I am stuck on what is q?