Lets us consider an example:
Suppose a 10 ohm bulb is connected across the terminals of a 10 V
battery having 2ohm internal resistance.
Then total reistance in series we know, R1 + R2
Thus, R net = 10+ 2 = 12 ohm
The, current across circuit = 10/12= 0.833 A
Now, Power is given by
Thus, power dissipated across internal resistance, P =
And, total power dissipated =
Thsu, percentage of pwer not avaible = 1.37/8.2 = 16.70%