Q 12-03-262JEE MainJEE Main 2019 (8 Apr, Shift 2)Easy
A cell of internal resistance $r$ drives current through an external resistance $R$. The power delivered by the cell to the external resistance will be maximum when
Answer: (B) $R = r$
$$P = \frac{E^2R}{(R + r)^2},\quad \frac{dP}{dR} = E^2\frac{(R + r) - 2R}{(R + r)^3} = 0 \Rightarrow R = r$$
This is the maximum power transfer condition.
Solution by Sreeraj P, M.Sc Physics