Power from a Cell

E=5 V  r=0.2 Ω 
(in ohm)
(in volt)
(in A)
(in W)
Quiz Potential difference across the external resistance

This increases (green curve) as the external resistance increases. (If you see the sum of the potential differences of R and r as E and that the individual potential differences should be in the ratio R:r, it would be obvious that V across R should increase as R increases) Current through it is

This decreases (yellow curve) with increase in external resistance. Power dissipated across the external resistance

and this increases (cyan curve) as R increases reaching a maximum value when R= r and then decreases.The maximum value of power is

A plot of i, V and P as R is varied are shown in the graph and the values of these quantities are indicated in the tabular form. You should be able to relate to these relations easily.