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Directions : (21-25)

Mechanism of Current flow in a conductor

Metals have a large number of free electrons nearly \[{{10}^{28}}\] per cubic metre. In the absence of electric field, average terminal speed of the electrons in random motion at room temperature is of the order of \[{{10}^{5}}\,m{{s}^{-1}}\]. When a potential difference V is applied across the two ends of a given conductor, the free electrons in the conductor experiences a force and are accelerated towards the positive end of the conductor. On their way, they suffer frequent collisions with the ions/atoms of the conductor and lose their gained kinetic energy. After each collision, the free electrons are again accelerated due to electric field, towards the positive end of the conductor and lose their gained kinetic energy in the next collision with the ions/atoms of the conductor. The average speed of the free electrons with which they drift towards the positive end of the conductor under the effect of applied electric field is called drift speed of the electrons.

Magnitude of drift velocity per unit electric field is :

A) current density

B) current

C) resistivity

D) mobility