

Explanation
(i) E.m.f is the work doone in taking a unit electric charge round a closed circuit. H is measured in volts.
(ii) Other sources of e.m.f. are; solar cells, fuel cells, dynamo or electric generators, thermocouple etc.
(b)

(c) (i) In open circuit Vo e.m.f of the cell.
In closed circuit V terminal p.d of the cell.
(ii) (a) I = \(\frac{E}{R + r}\)
(b) Maximum power dissipated in the cell occurs when the external resistance = the internal resistance of the cell i.e. R = r. Maximum power dissipated in the cell = IE
= \(\frac{E}{R + r} \times E = \frac{E^2}{R + r} = \frac{E^2}{2R}\)
Maximuim power dissipated in the external load
= I\(^2\)R = \(\frac{E^2R}{(R + r)^2}\)
= \(\frac{E^2R}{4R^2} = \frac{E^2}{4R}\)
(iii) Efficiency of the call = \(\frac{\text{power output}}{\text{power input}}\) x 100%
= \(\frac{2R}{E^2} \times \frac{E^2}{4R}\) x 100% = 50%

