A battery is connected across a conductor of non-uniform cross-sectional area. The quantity/quantities which remain(s) constant is/are
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → current only
In the steady state, charge cannot pile up anywhere in the conductor, so the same current crosses every cross-section (continuity of current), whatever its area.
The other quantities change with the area \( A \):
\( j = I/A, \quad E = \rho j = \rho I/A, \quad v_{d} = I/(neA) \)
So at a narrow section the current density, the electric field and the drift speed are all larger; only the current stays constant.
Note: A similar question was also asked in CUET (UG) 2025 on 15-05-2025 (Slot 2), and in CUET (UG) 2023 on 12-06-2023 (Slot 3).