A steady current flows in a conductor of non-uniform cross-section. The physical quantity which remains constant along the length is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Current only
In a steady flow no charge piles up anywhere, so the same charge crosses every cross-section per second: the current is the same at all sections of the conductor.
The other quantities change with the area A. The current is \( I = neAv_d \), so for a fixed I the drift velocity is \( v_d = I/(neA) \), which is larger where the conductor is narrower. The electric field is \( E = \rho J = \rho I/A \), which also varies inversely with A.
Hence only the current stays constant along the length.
Note: A similar question was also asked in CUET (UG) 2026 on 24-05-2026 (Slot 1), and in CUET (UG) 2025 on 15-05-2025 (Slot 2).