Q. The maximum power drawn out of the cell from a source is given by (where $r$ is internal resistance)
A) $E^{2}/2r$
B) $E^{2}/4r$
C) $E^{2}/r$
D) $E^{2}/3r$
Explanation
(b) $i = \frac{E}{r + R} \Rightarrow P = i^{2}R \Rightarrow P = \frac{E^{2}R}{(r + R)^{2}}$
Power is maximum when $r = R \Rightarrow P_{\max} = E^{2}/4r$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.