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

To calculate the resistance, we can use the formula relating power (P), voltage (V), and resistance (R):

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

Given that the power output of each lamp is 0.75W and using the potential difference calculated previously (1.5V), we can rearrange the formula to find R:

1. Recall the power formula:

   $0.75 = \frac{(1.5)^2}{R}$

2. Rearrange to find R:

   $R = \frac{(1.5)^2}{0.75}$

3. Calculation:

   $R = \frac{2.25}{0.75} = 3 \Omega$

Therefore, the resistance of each lamp is 3Ω.

To investigate how the resistance changes, the student could set up a circuit diagram that includes:

• A power supply,
• An ammeter to measure current,
• A voltmeter to measure potential difference across the lamp,
• The lamp itself connected in the circuit.

Method:

1. Connect the lamp to the power supply, including the ammeter in series and the voltmeter in parallel with the lamp.
2. Vary the voltage from the power supply and record the current flowing through the lamp.
3. For each voltage setting, measure and record the potential difference across the lamp.
4. Calculate the resistance using Ohm's law: $R = \frac{V}{I}$
5. Repeat the process for several settings and compare the results to find out how the resistance changes with the potential difference.