Drift Velocity
In a metal conductor, there is an extremely large number of free electrons. These free electrons move randomly with a thermal speed of the order of 10⁵ to 10⁶ m/s at room temperature. In any portion of the conductor,, the flow of electrons is so oriented that the average thermal velocity of a total number of free electrons in a conductor is zero. That is,
u=u₁+u₂+u₃+.........+un/n=0
where u₁, u₂, u₃, .........un are the thermal velocities of free electrons and n is the total number of free electrons.
When an electric flied is applied across the conductor, the free electrons accelerate in a direction opposite to the direction of the applied field. due to this acceleration, the electrons gain extra velocity butt for a short time because of the accelerated electrons colloid with each other free electrons or the ions in the conductor and during this collision, the extra velocity gained is destroyed. Again, the electron is accelerated and comes to rest after collision with ions. Therefore, the motion of electrons in a conductor under the influence of the electric field is like a pause and start motion. As a net result, the electrons acquire a small velocity called drift velocity(Vd) in the direction opposite to that of the applied electric flied. The flow of electrons with drift velocity from one end to another end of the conductor constitutes an electric current.
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