The diagram shows a circuit used to investigate the variation of current with potential difference for a filament lamp - Leaving Cert Physics - Question 4 - 2012

The component V is a variable resistor or rheostat. It is used to limit the current flowing through the circuit, allowing adjustments to the potential difference applied to the filament lamp.

The graph should have Potential Difference on the x-axis and Current on the y-axis. Each data pair from the table should be plotted accurately, and points should be connected smoothly to depict the trend. Make sure to label both axes clearly and indicate the units for voltage (V) and current (A).

The graph indicates that the relationship between current and potential difference for a filament lamp is non-linear. Initially, as the potential difference increases, the current also increases, but at a decreasing rate. This suggests that the filament lamp exhibits ohmic behavior only at lower voltages, as higher voltages result in a significant increase in temperature, leading to increased resistance.

To calculate the resistance, use Ohm's law, which states that resistance (R) is equal to the voltage (V) divided by the current (I). From the graph, find the current corresponding to a potential difference of 5.5 V. Assume the current is approximately 2.5 A:

$R = \frac{V}{I} = \frac{5.5 \text{ V}}{2.5 \text{ A}} = 2.2 \Omega$

Thus, the resistance of the lamp at 5.5 V is 2.2 ohms.