Alternative A
Question 3A
A circuit is connected as shown in the diagram above. With the length x of the constantan wire connected, the key is closed such that current passes in the circuit.
The current I, in the circuit is measured and recorded. Also the corresponding potential difference V across the constantan wire is measured and recorded.
The procedure is repeated for four other values of x to obtain the corresponding values of I and V.
Fig. 3(a) shows the values of Ii while fig. 3(b) shows the corresponding values of Vi
Fig. 3(a) shows the values of xi where i = 1, 2, 3, 4 and 5 respectively.
- Measure and record the values of xi.
- Read and record the values of Ii.
Also read and record the corresponding values of Vi
(b) (i) What happens to the resistance of a lamp as the current through it increases.
(ii) The current through the filament of an electric bulb is 3.0 A. Calculate the charge that passes through the filament in 5 minutes.
Observation
Part (a) This was popular question among the candidates. However, many candidates had difficulty in interpretation of the relationship among length of resistance wire, current passing through it and voltage across it.
Part (b) Candidates performance was above average. Candidates should good understanding in explaining what happens to the resistance of a lamp as the current through it increases. The numerical aspect in (bii) was fairly attempted.
b(i) What happens to the resistance of a lamp as the current through it increases
As the current through the lamp increases, its resistance also increases.
(ii) Q =It
= 3 x 5 x 60
= 900 C