The drift velocity measures the instantaneous speed of the electrons between the collisions they experience in the metal. the drift velocity is very slow, and a typically describes a microscopic displacement over a period of a second. the drift velocity measures the speed of the atomic nuclei drifting through the metal. the drift velocity is very fast and is directly responsible for the short time required an electrical signal to reach a light bulb when you flip a light switch from across the room. the drift velocity measures the rate at which electrons leave the surface of the metal. your answer