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 an intrinsic semiconductor, the charge carriers are either electrons only or holes only; both of them may not participate in conduction

Answer 1

Answer: (A), (C)

The drift speed of charge carriers is a very small fraction of the mean thermal agitation speed of the same charge carriers
The drift velocity is proportional to the electric field applied ordinarily

Let e denote the charge of an electron, m its mass, and E be the applied electric field then
$[V_d=(e\ast E\ast \varsigma \left)/m\right]$
where, $\left[V_d\right]$ denote the drift velocity of the electron and $\left[\varsigma \right]$ denote the average time elapse between successive collision of the electrons with each other.
On substituting values of E and $\left[\varsigma \right]$ we get the drift velocity which is of the order of millimetre per second which is a fraction of the thermal velocity of electron under normal condition .
And we can also see that drift velocity is directly proportional to the applied electric field.
No. of charge carriers per unit volume is not necessarily equal to the no. of atom per unit volume as their are divalent and trivalent metal atom. eg. aluminium
In intrinsic semiconductors both electrons and holes participate in conduction.