*Circuit diagram showing a battery, filament lamp, ammeter and variable resistor connected in series, with a voltmeter connected in parallel with the filament lamp.*The resistance of the variable resistor should be altered to change the values of the current flowing through the lamp. For different values of the resistance of the variable resistor, the current flowing through the lamp should be measured with the ammeter and the voltage across the lamp should be measured with the voltmeter. The resistance of the lamp can be calculated using the equation R = V / I. The resistance of the lamp should be calculated for a wide enough range of different currents that would allow for a valid conclusion to be made, perhaps by plotting the current and resistance values on a graph and drawing a line of best fit.