Arrange the following in a CORRECT sequence of processes for electrons in a conductor acquiring drift velocity in an electric field.
A. The electrons are accelerated until they collide with ions in the conductor. This sequence continues.
B. A battery is connected across the ends of the conductor
C. Hence on average the electrons in the conductor acquire drift velocity
D. The free electrons in the conductor move randomly before connecting the battery.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → D, B, A, C
Drift velocity is a small average velocity superimposed on random thermal motion, and it appears only after a field is applied across the conductor.
D — The free electrons in the conductor move randomly before connecting the battery. Their random velocities average to zero.
B — A battery is connected across the ends of the conductor. This sets up an electric field in the conductor.
A — The electrons are accelerated until they collide with ions in the conductor. This sequence continues. The field accelerates each electron afresh after every collision.
C — Hence on average the electrons in the conductor acquire drift velocity, directed opposite to the field.
So the order is D, B, A, C.
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 last result is surprising. It tells us that the electrons move with an average velocity which is independent of time, although electrons are accelerated. This is the phenomenon of drift and the velocity vd in Eq. (3.17) is called the drift velocity.”