Question

The random motion of holes and free electrons due to thermal agitation is called
(A) Diffusion
(B) Pressure
(C) Ionisation
(D) None of these

Answer 1

Hint : Thermal agitation tends to let electrons and holes to even out throughout the semiconductor. Diffusion is the movement of electrons and holes from a region of higher concentration to a region of lower concentration.

Complete step by step answer
In any material above absolute zero, there’s thermal agitation of the constituent of the material. The constituent could atoms, molecules, electrons, and for a semiconductor, holes. This thermal agitation of these constituents allows an even distribution of the electrons and holes of a semiconductor.
Diffusion – this is the movement of electrons and holes from a region of higher concentration to lower concentration. The drive which causes diffusion is the thermal agitation of the atoms or molecules or electrons and holes. Hence, this is why the thermal agitation is called diffusion.
Pressure – this is simply the amount of force exerted on a surface per unit area of that surface. In gases, the pressure exerted by a gas on a surface is indeed due to the thermal agitation of the atoms, hence why pressure is directly proportional to the temperature. However, in solids like semiconductor, this is mostly inexistent.
Ionisation – this is the ejection of electrons away from the orbit of an atom, hence giving the atom a net positive charge. This is caused by many things such as radiation.
From these, we can conclude that the random motion of holes and electrons due to thermal agitation is diffusion.
Hence, the correct option is A.

Note
For clarity, diffusion, as already defined, is actually the movement of the electrons from a region of higher concentration to a region of lower concentration and is not the thermal agitation itself. It is only caused by the thermal agitation of the electrons and holes.