16) 4 cells of identical emf E, internal resistance r are connected in series to a variable resistor. The following graph shows the variation of terminal voltage of the combination with the current output :
(a) What is the emf of each cell used?
(b) For what current from the cell, does maximum power dissipation occur in the circuit?
(c) Calculate the internal resistance of each cell.

a) for calculating the total emf of the cell
       when I=0 then, E=V=5.6 V for 4 cells.
       therefore emf of each cell= 5.6/4 = 1.4V
c) when I= 2A then terminal volatge is 0.
     and since while discharging E= V + Ir
                                                  5.6=0 + 2(4r)
                                                   r = 0.7 ohm 
b) for power to be maximum I= 1A since then P=VI= 2.8 watt(i.e. maximum)