CBSE 2025 · Region 4 · Set 1 · Q2 · 1 mark

A current flows through a cylindrical conductor of radius R. The current density at a point in the conductor is $\displaystyle \mathrm{j}=\alpha \mathrm{r}$ (along its axis) , here $\displaystyle \alpha$ is a constant and $\displaystyle \mathrm{r}$ is distance from the axis of the conductor. The current flowing through the portion of the conductor from $\displaystyle \mathrm{r}=0$ to $\displaystyle \mathrm{r}=\frac{\mathrm{R}}{2}$ is proportional to:

CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.