The candidates were expected to:
(i) set up a circuit diagram as shown in the diagram above;
(ii) read and record the value of Io in ampere to at least 1 decimal place;
(iii) evaluate and record the value of I¹ to 1 decimal place;
(iv) read and record five values of I in ampere to at least 1 decimal place in trend.
Trend: As R increases, I decreases;
(v) evaluate five values of I¹ to at least 3 significant figures.
(vi) present data in a composite and complete table and
showing at least I, I¹ and R;
(vii) correctly distinguish the graph axes , select reasonable scales, plot the five points and draw a line that best fits the points;
(viii) draw a large right angled triangle on the graph line, read Δ I¹
and ΔR and evaluate slope = Δ I¹
(ix) show and read the intercept on the vertical axis;
(x) evaluate k = c/s;
(xi) state any two of the following precautions in the correct form of speech:
- I ensured firm support of pendulum;
- Ensured tight connections/clean terminals
- Zero error of ammeter noted and corrected for;
- Parallax error in ammeter avoided.
b (i) The electromotive force of a cell is the work done in driving a unit of electric charge round a complete circuit OR
The electromotive force is the total work done in driving one coulomb of electricity round the circuit OR
The total energy per coulomb obtained from a cell or battery.
(ii) A galvanometer adapted to read as an ammeter.
This experiment was very popular among the candidates. However, some candidates failed to record their initial ammeter reading; record the reciprocal of I to the required decimal places; evaluate k = c/s.
In part b, many candidates failed to explain electromotive force of a cell correctly. Some candidates could not explain with the aid of a labeled diagram how a galvanometer may be adapted to read as an ammeter.