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
Explanation:
For a conductor of non-uniform cross-section, the current $I$ remains constant throughout because of the principle of conservation of charge.
However, the drift speed $v_d$ and the electric field $E$ vary along the conductor since they depend on the cross-sectional area $A$ as
$ I = n e A v_d $
Thus, when $A$ changes, $v_d$ and $E$ change, but $I$ remains constant.