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The drift velocity deals with the average velocity of a particle, such as an electron, due to an electric field. In general, an electron will propagate randomly in a conductor at the Fermi velocity. [5] Free electrons in a conductor follow a random path. Without the presence of an electric field, the electrons have no net velocity.
The final result is that the electron moves with a finite average velocity, called the drift velocity. This net electron motion is usually much slower than the normally occurring random motion. The two charge carriers, electrons and holes, will typically have different drift velocities for the same electric field.
As a result, ions (of whatever mass and charge) and electrons both move in the same direction at the same speed, so there is no net current (assuming quasineutrality of the plasma). In the context of special relativity , in the frame moving with this velocity, the electric field vanishes.
As a result, there is a definite small drift velocity of electrons, which is superimposed on the random motion of free electrons. Due to this drift velocity, there is a net flow of electrons opposite to the direction of the field. The drift speed of electrons is generally in the order of 10 −3 meters per second whereas the thermal speed is on ...
Because of collisions between electrons and atoms, the drift velocity of electrons in a conductor is on the order of millimeters per second. However, the speed at which a change of current at one point in the material causes changes in currents in other parts of the material, the velocity of propagation , is typically about 75% of light speed ...
Consider electrons in a constant electric field E. Electrons will flow (i.e. there is a drift current) until the density gradient builds up enough for the diffusion current to exactly balance the drift current. So at equilibrium there is no net current flow: + =
Ballistic electrons behave like light in a waveguide or a high-quality optical assembly. Non-ballistic electrons behave like light diffused in milk or reflected off a white wall or a piece of paper. Electrons can be scattered several ways in a conductor. Electrons have several properties: wavelength (energy), direction, phase, and spin orientation.
This means that a sodium ion in an electric field of 1 V/m would have an average drift velocity of 5.19 × 10 −8 m/s. Such values can be obtained from measurements of ionic conductivity in solution. Electrical mobility is proportional to the net charge of the particle.