Question

A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/ quantities constant along the length of the conductor is/are

• A. Current, electric field and drift speed
• B. Drift speed only
• C. Current and drift speed
• D. Current only

Answer 1

Answer: (D)

If $E$ be electric field, then current density $j=\sigma E$
Also we know that current density $j=\frac{i}{A}$
Hence $j$ is different for different area of cross-sections.
When $j$ is different, then $E$ is also different. Thus $E$ is not constant.
The drift velocity $v_d$ is given by $v_d=\frac{j}{ne}=$ different for different $j$ values.
Hence only current $i$ will be constant.