Q 12-03-282JEE MainJEE Main 2018 (15 Apr, Shift 2)Easy
A copper rod of cross-sectional area $A$ carries a uniform current $I$ through it. At temperature $T$, if the volume charge density of the rod is $\rho$, how long will the charges take to travel a distance $d$?
Answer: (C) $\dfrac{\rho dA}{I}$
Current $I = \rho A v_d$, where $\rho$ is the charge per unit volume of the moving carriers. So
$$v_d = \frac{I}{\rho A}, \qquad t = \frac{d}{v_d} = \frac{\rho dA}{I}$$
Solution by Sreeraj P, M.Sc Physics