Question

The following graph shows the variation of terminal potential difference V, across a combination of three cells in series to a resistor, versus the current, i:

(i) Calculate the emf of each cell.
(ii) For what current i will the power dissipation of the circuit be maximum ?

Answer 1

(i) Let ε be emf and r the internal resistance of each cell. The equation of terminal potential difference

where r_int is effective (total) internal resistance. 

From fig., when i = 0,V = 6.0V

(ii) For maximum power dissipation, the effective internal resistance of cells must be equal to external resistance.