10 (a) 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 of each lamp, we can use the power formula:

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

Rearranging the formula gives:

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

Substituting the known values:

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

Thus, the resistance of each lamp is 3Ω.

To investigate how resistance changes with potential difference, the student can set up a circuit as follows:

1. Circuit Components:

   • Connect a single filament lamp in series with a variable resistor (rheostat) and an ammeter.
   • Connect a voltmeter across the lamp to measure the potential difference.
   • Include a power supply.

2. Method:

   • Start with the variable resistor set to its maximum value to limit current flowing through the lamp.
   • Measure the current using the ammeter and the potential difference using the voltmeter.
   • Gradually decrease the resistance and repeat the measurements of current and voltage.
   • Calculate resistance at each step using Ohm's law:

   $R = \frac{V}{I}$

   • Record the data and create a graph of resistance against potential difference.