Question

It is known that the drift velocity of electrons is only a few mm/s for a current of a few amperes. Then how is it possible that a current is established almost instantaneously when a circuit is closed? For example, a bulb glows as soon as the connection is switched on. Explain.

Answer 1

The conductor is full of ‘'free electrons”. If we switch on the voltage then the electric field is generated in the entire conductor at the speed of light. Here, every single free electron acquire drag velocity immediately and hence we get the current instantly

Complete step-by-step solution:
In this, because the conduction band of the metal in the wire is crammed full of electrons. When we turn on the switch, the electrons are given a “push” and it’s the effect of that push that is passed down the line.
Here, not an individual electron has traveled and reached the light from the switch to turn on the light.
Suppose we have a tube(cylinder) open at both ends filled with water and kept in gravity less space. As it is obvious water will not spill out if there is no gravity.
Now when we add a single drop of water to one end a drop of water will come out of the other end.
The same is the case with electrons in a wire. It is filled with electrons. when one electron enters from one end then the one-electron will leave from the other end, although the absolute velocity of electrons is in mm/sec.

Note:

It does not require individual electrons to move from one end of the conductor to the other.
Every free electron in the conductor accelerates because of the effect of the electric field until it collides with a positive ion and hence its drift speed reduces.
The electrons travel a continuous cycle of collision and successive loss of drift speed until an average drift speed is reached.