n general the electrons exhibit a random motion. Thus it is assumed that electrons moving in a certain direction is approximately equal to the number of electrons moving in the opposite direction. So it is said that there is no net flow of electrons in this case, in the absence of an electric field.
But in an electric field,
while each electron exhibits a random motion, the electrons are further exerted a force on by the electric field, in an opposite direction.They get “drifted” in the direction opposite to that of the applied electric field.
DRIFT VELOCITY =Th average velocity gained by the free electrons of a conductor, with which the electrons get drifted under the influence of an electric field, applied externally across the conductor.
It is of the order of 1 mm / s = 10^(-3) m / s
2)The best way to convey the idea of what is happening when current flows in a conductor is to visualize the process. What is happening is that the atoms that make up the material of the conductor like copper wire for example, have an outermost shell of electrons known as the “valance shell”. Depending on the number of electrons in the valance shell will determine whether the material will be a conductor, an insulator, or something in between. A good conductor will have many electrons in the valance shell and an insulator will have few. When there are many valance shell electrons the material will more easily give up an electron and pass it to the next nearby valance shell. When the electron moves to the next adjoining valance shell it will bump one of the existing electrons from that shell on to the next one, and this continues on down the line until at the end of the conductor, an electron is ejected to the delivery point which will generally be made of a conductive material as well and will continue to the point of delivery of the electron to it’s final destination. For visual representation at a greatly simplified level, please imagine that the conductor is a straw full of popcorn seeds. When you hold the straw horizontally, and push popcorn seeds into the the end of the straw, they in turn push the seed already in the straw through the straw. If they straw is full of seeds and you push in another seed at one end, a seed will have to pop out the other end. The pressure of pushing the seed in is like the pressure of voltage on the electron, and the seeds of corn are like the chain of electrons in the valance shell of a conductor that push their way to the end. This is highly simplified however it works for visualization.