Suppose i1 , i2 and i3 be the currents in given three cells and r be this current through external resistance R. Applying Kirchoff’s first law to the point, we have A
i = i1 + i2 + i3 .....(1)
Applying second law to the mesh E1 A R B E1 , we have
i1 r1 + iR = E1 .....(2)
Similarly, i2 r2 + iR = E2 (Mesh E2 A R B E2) .....(3)
and i3 r3 + iR = E3 (Mesh E3 A R B E3) .....(4)
Divides equation (2) by r1 , equation (3) by r2 and equation (4) by r3 and adding we get