An electron enters a uniform magnetic field B at angle θ to B with speed v. The pitch of its helical path is

1. Decompose velocity: parallel v∥ = v cos θ and perpendicular v⊥ = v sin θ. 2. The perpendicular component drives circular motion with period T = 2πm/(eB). 3. The parallel component moves the centre of the circle linearly at v cos θ. 4. Pitch = distance moved along the axis in one period = v cos θ · T = 2πm v cos θ/(eB). _Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", §4.3_