The question is not popular among the students. The observation was well attempted by the candidates, a few however forgot to read and record the emf of the battery used but were able to measure I and V correctly as increases. Evaluation of log I and logV was not done to the required number of decimal places.
Plotting of the graph of log I against log V was poorly attempted because of its positive and negative values. Few of the candidates committed systematic error in plotting this graph while most responding candidates plotted the graph wrongly. Candidates were able to state correctly the precautions in acceptable language.
In the short response questions, candidates showed clearer understanding of Ohm’s law and were able to list examples of non – Ohmic conductor.
Majority of the responding candidates were able to state correctly the effect of increase in the value of x on the brightness of the bulb but could not give reason why brightness of the bulb increases.
In part (a) candidates were required among other things, to:
- Measure and record the emf of the battery in volts to at least 1 d.p
- Read and record six values of , V and I to at least 1 d.p and in trend.
(Trend as increases, V and I also increases)
- Evaluate six values of log I and log V to at least 3 d.p.
- Record ,V, I, log V and log I in composite table
- plot six points correctly using reasonable scale
- Draw line of best fit on distinguished axes
- Determine the slope of the graph using large right angled triangle and recording of the
intercept on the vertical axis.
State any two precautions in acceptable language
- Ensured clean/tight terminals
- Open key when reading was not taken
- Avoided parallax error in ammeter/voltmeter
- Avoided sliding of jockey on the potentiometer wire.
b(i) - Brightness of the bulb increases
- voltage/current through the bulb increases
(ii) Devices that do not obey Ohm’s law
Diode
Transistor
Thyristor
Capacitor
Thermistor
