Question

how is it that an electric bulb lights up as soon as we turn the switch on if the drift speed is 1mm /s^2

Answer 1

It is really just the limits of human vision perception....with out instrumentation we cant see the delay.

Answer 2

It may seem as if the bulb lights up instantaneously as you flip the switch on, but there is actually a small time delay. You may think that the light from the bulb reaches you instantaneously, but no, even light as a finite speed. Just think, if they give you a drift speed of 1mm/s, then you know that the electrons have a finite speed in a wire. So we now know it can't be instantaneous.

Answer 3

wire connected with bulb already contain electrons when we switch on the bulb electrons near filament reaches it with in no time