Electron beam *
A beam of 9.5 megaelectron-volt (MeV) electrons (γ≈20), amounting as current to 0.05μA, is traveling through vacuum. The transverse dimensions of the beam are less than 1 mm, and there are no positive charges in or near it.
(a) In the lab frame, what is the average distance between an electron and the next one ahead of it, measured parallel to the beam? What approximately is the average electric field strength 1 cm away from the beam?
(b) Answer the same questions for the electron rest frame.