The radius of the orbit of a charged particle in a magnetic field is related to the momentum of the particle by

p = BqR           39-41

This equation holds classically for p = mu and relativistically for p = m₀u/√1 – u²/c². An electron with kinetic energy of 1.50 MeV moves in a circular orbit perpendicular to a uniform magnetic field B = 5 × 10^-3 T.

(a) Find the radius of the orbit.

(b) What result would you obtain if you used the classical relations p = mu and K = p²/2m?