Question

what is the total emf when 3 cellseach of voltages 1v,1.5v,2v are connected in a)series and b)paralell

Answer 1

emf=2V
r=?
R=5 ohm
terminal voltage=5V
Let internal resistance be r ohm
effective resistance of each three cells in parallel, r=r/3
total resistance = r/3+R

V=emf*R/r+R

terminal voltage   V=emf*R/(r/3)+R

1.5=2*5/(r/3)+5
 
r=5 ohm

Answer 2

FOR PARALLEL CONNECTION

applying superposition we can split it in two circuit . since current I1 and I2 are different hence a circulating current will flow