What is the maximum power output than can be obtained from a cell of emf E and internal resistance r?

Options

A. `2E^(2)/r`
B. `E^(2)/2r`
C. `E^(2)/4r`
D. None of these

Answer

C

Explanation

Current `i=(E )/((R+r))` and power `P = i^(2)R`
`P= (E^(2))/((R+r)^(2))R`
Power is maximum, when r = R or `P_("max")=(E^(2))/(4r)`