Figure 18 shows identical filament lamps connected together to a 12V power supply - Edexcel - GCSE Physics - Question 10 - 2018 - Paper 1

To find the resistance, we can use the formula relating power (P), potential difference (V), and resistance (R). The formula is:

$P = \frac{V^2}{R}$

Rearranging this gives us:

$R = \frac{V^2}{P}$

Substituting the values from part (i) and the given power:

$R = \frac{(1.5V)^2}{0.75W} = \frac{2.25}{0.75} = 3 \Omega$

To investigate how the resistance of a single lamp changes with voltage, the student can set up a simple circuit consisting of:

1. A variable power supply to adjust the voltage.
2. An ammeter to measure the current flowing through the lamp.
3. A voltmeter connected in parallel across the lamp to measure the potential difference.
4. The filament lamp under test.

The student should vary the voltage from the power supply and record the readings of current and voltage for each setting. Using Ohm's Law, the resistance at each voltage can be calculated as:

$R = \frac{V}{I}$ for each set of measurements. This data can then be used to plot a graph of resistance against potential difference, from which trends can be analyzed.