A charged particle moves in a uniform field B such that its velocity has a component v∥ parallel to B. The distance moved along the field in one full revolution (the pitch) is:

1. The parallel velocity component $v_\parallel$ is unaffected by the field, giving helical motion. 2. The pitch is the axial distance per revolution: $p = v_\parallel T$. 3. The period is $T = \dfrac{2\pi m}{qB}$. 4. Therefore $p = v_\parallel \times \dfrac{2\pi m}{qB} = \dfrac{2\pi m v_\parallel}{qB}$. _Source: syllabus Physics Ch 4 "Moving Charges and Magnetism", p.140_