Question

Explain the working of a velocity selector.

Answer 1

Velocity selector (or a Wien filter ) is a device used to distinguish the particles with different speed. The main part of the device is a medium with perpendicular electric and magnetic fields in it. When a charged particle moves through the filter, its trajectory gets curved depending on the speed of the particle. The direction to which the particle will turn depends on which force is bigger, electrostatic forces $F=qE$ or electromagnetic force $F = qvB$