Question

Electric current is due to flow of charge carriers in the conductors. Which of the following is/are correct?
(A) The drift speed of charge carriers is a very small fraction of the mean thermal agitation speed of the same charge carriers.
(B) The number of charge carriers per unit volume is always the same as the number of atoms of the conductor per unit volume.
(C) The drift velocity is proportional to the electric field applied ordinarily.
(D) In intrinsic semiconductors, the charge carriers are either electrons only or holes only; both of them may not participate in conduction.

Answer 1

According to the question, we will show numerically how electric current is caused by the passage of charge carriers in conductors, and then choose the proper choice using the electron drift velocity formula.

Complete answer:
Let $e$ denote the charge of an electron, $m$ its mass and $E$ be the applied electric field then
$[{V_d} = \dfrac{{(e * E * \varsigma )}}{m}]$
where, ${V_d}$ denotes the drift velocity of the electron and,
$\varsigma$ denotes the average time elapse between successive collisions of the electrons with each other.
On substituting values of $E$ and $\varsigma$ we acquire a drift velocity of a few millimetres per second, which is a small fraction of the thermal velocity of an electron in normal conditions.
It's also clear that drift velocity is proportional to the applied electric field.
The number of charge carriers per unit volume does not necessarily equal the number of atoms per unit volume since divalent and trivalent metal atoms exist. Take, for example, aluminium.
In intrinsic semiconductors, both electrons and holes participate in conduction.
As a result, charge carrier drift speed is a very small percentage of their mean thermal agitation speed, and the number of charge carriers per unit volume is always the same as the number of atoms in the conductor per unit volume.
Hence, the correct options are option (A) and option (B).

Note:
When an electric current travels through a conductor, it moves as a drift of free electrons across the metal. Electricity flows freely through a conductor because the electrons are free to move about. When electrons flow over a conductor, they create an electric current.