AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), 2023: Question 4

13 marks · Standard Demand difficulty · Extended Answer

Identify a thermistor, plan an investigation into its resistance-temperature relationship, interpret a graph, and perform power calculations.

Practise this question

Question

A physics exam question about thermistors and electrical circuits. It includes four circuit symbols (switch, diode, thermistor, LDR), a diagram of experimental equipment (resistance meter, temperature sensing component, beaker of iced water, kettle, and thermometer), and a line graph showing resistance in ohms against temperature in degrees Celsius. The graph shows a non-linear curve where resistance decreases from 280 ohms at 0°C to approximately 30 ohms at 50°C. The text asks students to identify symbols, define current, plan a method, interpret the graph, and calculate current using the power equation.
Question text

04 A gardener wanted to build an electrical circuit to monitor the temperature in a

greenhouse.

04.1 Which symbol represents an electrical component with a resistance that decreases as

its temperature increases?

[1 mark]

Tick ( ) one box.

04.2 When the resistance of an electrical circuit decreases, the current in the

circuit increases.

Complete the sentence.

Choose the answer from the box.

[1 mark]

charge energy potential difference power

Electrical current is a flow of .

04.3 The gardener wanted to find how the resistance of the component varies with

temperature.

Figure 4 shows the equipment used by the gardener.

Figure 4

The resistance meter displays the resistance of the component.

Plan a method the gardener could use to find how the resistance of the component

varies with temperature.

[4 marks]

Figure 5 shows how the resistance of the component varies with temperature.

Figure 5

04.4 Complete the sentence.

Choose the answer from the box.

[1 mark]

linear non-linear directly proportional

The relationship between the temperature and the resistance of the component

is 21 .

04.5 The temperature in the greenhouse changed from 10 °C to 30 °C.

Determine the change in resistance of the component between these temperatures.

Use Figure 5.

[2 marks]

Change in resistance = Ω

The gardener builds a circuit that switches a heater on when the greenhouse gets

too cold.

Use the Physics Equations Sheet to answer questions 04.6 and 04.7.

04.6 Write down the equation that links current (I), potential difference (V) and power (P).

[1 mark]

04.7 The power of the heater is 2900 W.

The potential difference across the heater is 230 V.

Calculate the current in the heater.

[3 marks]

Current = A

Mark scheme

Show the mark scheme The mark scheme for question 4. It lists the correct symbol as the thermistor (rectangle with a diagonal line and horizontal flat ends). It defines current as a flow of 'charge'. The method for 04.3 requires placing the component in water, recording temperature and resistance, and repeating at different temperatures using a kettle. It identifies the graph relationship as 'non-linear'. For 04.5, it shows the calculation 200 - 80 = 120 ohms. For 04.6, the equation is P = V I. For 04.7, it shows the calculation 2900 / 230 = 12.6... A, allowing 13 A.

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 1 AO1

6.2.1.1

AO /

Spec. Ref.

04.2 charge 1 AO1

6.2.1.2

AO /

Spec. Ref.

04.3 place the component / 1 AO3

thermistor in the water / beaker 6.2.1.4

record the temperature (of the allow place the thermometer in 1

water) using the thermometer the water / beaker and record

the temperature

record / measure the resistance 1

(using the resistance meter)

change the temperature of the 1

water (using the kettle) and

repeat the measurements (of

temperature and resistance)

AO /

Spec. Ref.

04.4 non-linear 1 AO1

– OMBINED SCIENCE: TRILOGY – 1F – 6.2.1.4

AO /

Spec. Ref.

04.5 (resistance changes from) 1 AO2

200 ( ) to 80 ( ) 6.2.1.4

change in resistance = 120 ( ) 1

AO /

Spec. Ref.

04.6 power = potential difference × 1 AO1

current 6.2.4.1

or

P = V I

AO /

Spec. Ref.

04.7 2900 = 230 × I 1 AO2

6.2.4.1

2900

I = 1

I = 12.6… (A) allow 13 (A) 1

Total Question 4 13

How to answer it

Electricity: Thermistors and Power

What this question tests

This question assesses your ability to identify circuit symbols, define electrical current, design a practical investigation for resistance, interpret non-linear graphs, and perform power calculations using the standard physics equation sheet.

Part 4.1 & 4.2: Recall

Symbols and Definitions

4.1 Correct Symbol

The third box down: A rectangle with a diagonal line that has a flat horizontal "foot" at the bottom.

This is the symbol for a thermistor.

4.2 Correct Word

Electrical current is a flow of charge.

💡 Key Knowledge

  • Thermistor: A "thermal resistor". Its resistance decreases as temperature increases.
  • Current (I): Measured in Amps (A). It is the rate of flow of electrical charge (Q).

❌ Common Errors

  • Confusing the thermistor symbol with a Variable Resistor (which has an arrow through it).
  • Saying current is a flow of "energy" or "potential difference".
Part 4.3: Required Practical Skills

Planning a Method

How does resistance vary with temperature?

🧠 Exam Technique: Using the Diagram

When a question provides a diagram of equipment (Figure 4), your method must use that equipment. If they give you a kettle and iced water, they expect you to explain how to change the temperature using them.

✅ Model Answer (4 Marks)

  1. Place the thermistor (temperature sensing component) into the beaker of iced water.
  2. Measure the temperature using the thermometer and the resistance using the resistance meter.
  3. Add hot water from the kettle to the beaker to increase the temperature.
  4. Record the new temperature and resistance. Repeat this for several different temperatures.

⭐ Examiner Insight

Top-level responses clearly stated that both variables (temperature and resistance) must be recorded at each step. Simply saying "change the temperature" isn't enough; you must explain how (e.g., adding hot water).

Part 4.4 & 4.5: Graph Analysis

Interpreting the Data

4.4 Relationship

The relationship is non-linear.

Because the graph is a curve, not a straight line.

4.5 Calculation Step-by-Step

  1. Find Resistance at 10°C: Look at the x-axis for 10, go up to the curve, then left to the y-axis.
    Value = 200 Ω
  2. Find Resistance at 30°C: Look at the x-axis for 30, go up to the curve, then left to the y-axis.
    Value = 80 Ω
  3. Calculate the change:
    200 - 80 = 120 Ω
Mark 1: Identifying 200 and 80 from graph.
Mark 2: Final answer 120.
Part 4.6 & 4.7: Calculations

Power, Voltage, and Current

4.6 The Equation

Power = Potential Difference × Current

Symbol form: P = V × I

4.7 Calculating Current

Step 1: Substitute the values into the equation
2900 = 230 × I

Step 2: Rearrange to find I
I = 2900 / 230

Step 3: Final Answer
I = 12.6 A (or 13 A)

🧠 Calculation Tip

Always write the formula first. Even if you make a mistake in the division, you can still get a "substitution mark" for putting the numbers in the right place.

❌ Common Trap

Don't forget the unit! The question provides "A" for Amps, but if it didn't, you would lose a mark for omitting it. Also, ensure you don't swap the numbers (doing 230 / 2900 by mistake).

Topics

Physics · P2: Electricity

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.