A steady current flows in a metallic conductor of non-uniform cross-section. The quantity that is constant along the length is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Current only
In a steady current, charge cannot pile up anywhere, so the same charge passes every cross-section per second: the current is the same along the whole length. The quantities that involve the area change from section to section.
\( \displaystyle v_d = \frac{I}{n e A} \qquad E = \rho\,J = \frac{\rho\,I}{A} \)
Both are larger where the conductor is narrower.
Option (1) Both current and electric field — Incorrect. The field \( E = \rho I/A \) changes with the area.
Option (2) Drift speed only — Incorrect. The drift speed \( I/(neA) \) changes with the area.
Option (3) Both current and drift speed — Incorrect. The current is constant, but the drift speed is not.
Option (4) Current only — Correct. Only the current is the same at every cross-section.
Note: A similar question was also asked in CUET (UG) 2026 on 24-05-2026 (Slot 1), and in CUET (UG) 2023 on 12-06-2023 (Slot 3).