Identify the correct statements
(A) Electric current arises due to the continuous flow of electrons or ions.
(B) A current flows through a conductor only when there is an electric field within the conductor.
(C) The drift velocity of electrons is directly proportional to the applied electric field.
(D) The average thermal velocity of the electrons in a conductor is zero.
(E) In the absence of an electric field, the electrons in a conductor are at rest.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C) and (D) only
(A) Electric current arises due to the continuous flow of electrons or ions. — Correct. Current is the rate of flow of charge, and the carriers can be electrons (metals) or ions (electrolytes).
(B) A current flows through a conductor only when there is an electric field within the conductor. — Correct. Without a field the free electrons have no net drift, so there is no current.
(C) The drift velocity of electrons is directly proportional to the applied electric field. — Correct. \( v_d = \mu E \), where \( \mu \) is the mobility of the electrons.
(D) The average thermal velocity of the electrons in a conductor is zero. — Correct. The thermal motion is random in all directions, so the vector average of the velocities is zero.
(E) In the absence of an electric field, the electrons in a conductor are at rest. — Incorrect. Even without a field the free electrons move randomly with large thermal speeds; they are not at rest.
NCERT (2026-27):
Electric Currents in Conductors – “… These materials, generally called conductors, develop electric currents in them when an electric field is applied. … There are, however, other types of conductors like electrolytic solutions where positive and negative charges both can move.”
Electric Currents in Conductors – “… Consider first the case when no electric field is present. The electrons will be moving due to thermal motion during which they collide with the fixed ions.”
Drift of Electrons and the Origin of Resistivity – “… If we consider all the electrons, their average velocity will be zero since their directions are random.”
Drift of Electrons and the Origin of Resistivity – “… Thus, averaging Eq. (3.16) over the N-electrons at any given time t gives us for the average velocity vd
\( \displaystyle \mathbf{v}_d \equiv \left(\mathbf{V}_i\right)_{\text{average}} = \left(\mathbf{v}_i\right)_{\text{average}} - \frac{e\mathbf{E}}{m}\left(t_i\right)_{\text{average}} = 0 - \frac{e\mathbf{E}}{m}\tau = -\frac{e\mathbf{E}}{m}\tau \qquad (3.17) \)”