let m is the mass of the proton, b is the magnetic field, e is the electric charge, v is the velocity of the proton and r is the radius of the path in the magnetic field the period of the motion, the time between one kick to the right and the next kick in the same direction, does not depend on the current speed of the proton at speeds small compared to the speed of light. as a result, we can place across the dees a simple sinusoidal potential difference having this period and achieve continual acceleration out to the maximum radius of the cyclotron. one of ernest lawrence's first cyclotrons, built in 1932, had a diameter of only about 30 cm and was placed in a magnetic field of about 1 t. q1. what is the formula for the magnetic force acting on the proton?