JAMB Physics 2011 Paper

Concept:When similar cells are connected in parallel, the total e.m.f. is the same as one cell, while the total internal resistance is reduced like resistors in parallel.Explanation:Total e.m.f. in parallel connection equals the e.m.f. of one cell.So, total e.m.f. $= 2\,\text{V}$.For three cells, each with internal resistance $2\,\Omega$, in parallel:$$\frac{1}{r} = \frac{1}{2} + \frac{1}{2} + \frac{1}{2} = \frac{3}{2}$$Therefore, total internal resistance:$$r = \frac{2}{3} \approx 0.67\,\Omega \approx 0.7\,\Omega$$Answer:Total e.m.f. is $2\,\text{V}$ and total internal resistance is approximately $0.7\,\Omega$.Correct option: B.