1. A student investigated how the current in a filament lamp varied with the potential difference across the filament lamp. Figure 1 shows part of the circuit used.
i- Complete Figure 1 by adding an ammeter and a voltmeter. Use the correct circuit symbols.
[3 marks]
ANSWER
Always remember, ammeter is connected in series whereas the voltmeter is connected in parallel to the circuit.
Figure 2 box shows some of the results.
ii- The student reversed the connections to the power supply and obtained negative values for the current and potential difference.
Draw a line on Figure 2 to show the relationship between the negative values of current and potential difference.
[2 marks]
ANSWER
As the connections are reversed to the power supply, the values obtained would be negative of both the currents and potential difference. Therefore, we will choose any one set of coorfinate from the graph and mark the negative of it on the graph. As in my case, I have choosen (4, 0.2) point and has marked the inversed of it (-4, -0.2). this would now help to complete the curve path of the graph in the negative axes.
iii- Write down the equation which links current (I), potential difference (V) and resistance (R).
[1 mark]
ANSWER
iv- Determine the resistance of the filament lamp when the potential difference across it is 1.0 V. Use data from Figure 2.
[4 marks]
SOLUTION
Rearranging the equation to find resistance.
v- A second student did the same investigation. The ammeter used had a zero error. What is meant by a zero error?
[1 mark]
ANSWER
Ammeter is displaying a reading when not connected to the circuit.
