Which of the following characteristics of electron determines the current in a conductor?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Drift velocity alone
The current in a conductor is related to the drift velocity of the free electrons:
\( \displaystyle I = n\,e\,A\,v_d \)
The thermal velocities of the electrons are large but random in direction; averaged over all the electrons they add up to zero, so they carry no net charge across any cross-section. Only the small, steady drift superimposed by the electric field gives a net flow of charge. Hence the current is determined by the drift velocity alone.
Note: A similar question was also asked in CUET (UG) 2023 on 31-05-2023 (Slot 2).
NCERT (2026-27):
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 – “… This is the phenomenon of drift and the velocity vd in Eq. (3.17) is called the drift velocity. Because of the drift, there will be net transport of charges across any area perpendicular to E. … Hence,
\( \displaystyle I\,\Delta t = +\,n\,e\,A\,|v_d|\,\Delta t \qquad (3.18) \)”