AQA GCSE Combined Science: Trilogy Physics Paper 1 (Foundation), June 2025: Question 4
15 marks · Standard Demand difficulty · Short Answer
Answer questions about a kettle connected to the mains supply, including mains frequency, wire insulation colours, electrical power and current calculations, specific latent heat of vaporisation, and efficiency.
Practise this questionQuestion
Question text
04 Figure 5 shows a plastic kettle.
The kettle is connected to the mains electricity supply.
Figure 5
04.1 What is the frequency of the UK mains electricity supply?
[1 mark]
Tick ( ) one box.
25 Hz
50 Hz
75 Hz
100 Hz 16
04.2 The cable that connects the kettle to the plug contains two insulated wires.
Draw one line from each wire to the colour of the insulation on the wire.
[2 marks]
Use the Physics Equations Sheet to answer questions 04.3 and 04.4.
04.3 Write down the equation that links current (I), potential difference (V) and power (P).
[1 mark]
04.4 The power of the heating element in the kettle is 2100 W.
The potential difference across the heating element is 230 V.
Calculate the current in the heating element.
Give your answer to 2 significant figures.
[4 marks]
Current (2 significant figures) = A
04.5 The kettle is designed to switch off when the water reaches boiling point.
Before the kettle switches off, 0.0080 kg of water changes state.
The energy transferred to change the state of the water is 18 000 J.
Calculate the specific latent heat of vaporisation of the water.
Use the Physics Equations Sheet.
[3 marks]
Specific latent heat of vaporisation18 = J/kg
04.6 A different kettle is used to heat some water.
The useful output energy transferred to the water is 75 600 J.
The total input energy transferred by the kettle is 84 000 J.
Calculate the efficiency of the kettle.
Use the equation:
useful output energy transfer
efficiency =
total input energy transfer
[2 marks]
Efficiency =
04.7 Explain one advantage of electrical appliances having a high efficiency.
[2 marks]
Mark scheme
Show the mark scheme
Question 4
AO /
Question Answers Extra information Mark
Spec. Ref.
04.1 50 Hz 1 AO1
6.2.3.1
AO /
Question Answers Mark
Spec. Ref.
04.2 AO1
6.2.3.2
do not accept more than one line from a box on the left
AO /
Spec. Ref.
04.3 power = potential difference × current 1 AO1
6.2.4.1
or
P =VI – – 8464/P/1F –
AO /
Spec. Ref.
04.4 2100 = 230 × I 1 AO2
6.2.4.1
2100 1
I =
I = 9.13… 1
I = 9.1 (A) allow an answer calculated 1 13
using the numbers from the
question given to two significant
figures
AO /
Spec. Ref.
04.5 18 000 = 0.0080 × L 1 AO2
6.3.2.3
18 000 1
L =
0.0080
L = 2 250 000 (J/kg) allow 2 300 000 1
AO /
Spec. Ref.
04.6 75 600 1 AO2
efficiency =
84 000 6.1.2.2
efficiency = 0.9 1
OR
75 600
efficiency = × 100 (1)
84 000
efficiency = 90% (1) – – 8464/P/1F –
AO /
Spec. Ref.
14 allow power for energy
04.7 throughout
less energy is wasted 1 AO1
(so) costs less to run allow so the appliance is used 1 AO2
or for less time
(so) uses less electricity / 6.1.2.1
energy 6.1.2.2
6.2.4.2
Total Question 4 15
How to answer it
Kettle Physics: Domestic Electricity, Latent Heat & Efficiency
This 15-mark question assesses foundational concepts across Electricity, Particle Model of Matter, and Energy:
- Recall of UK mains electricity specifications: standard frequency (Hz) and three-core cable colour coding.
- Electrical power calculations: recalling and rearranging P = V × I to find current, plus applying rounding to significant figures.
- Specific latent heat: selecting and rearranging E = m × L to calculate energy needed for a change of state.
- Energy efficiency: calculating numerical efficiency and evaluating the economic and environmental benefits of energy-efficient appliances.
UK Mains Electricity Supply Frequency
Multiple Choice Recall
✅ Correct Answer
50 Hz
💡 Key Knowledge
- UK mains electricity is an alternating current (a.c.) supply.
- Frequency = 50 Hz (cycles per second).
- Potential difference (voltage) = 230 V.
❌ Common Errors
- Confusing frequency (50 Hz) with voltage (230 V).
- Guessing 25 Hz or 100 Hz due to unfamiliarity with standard UK grid constants.
Plug Wiring Insulation Colours
Matching Lines Question
✅ Correct Connections
| Wire | Correct Insulation Colour |
|---|---|
| Live | Brown |
| Neutral | Blue |
(Green and yellow stripes is the Earth wire, which is not connected in a 2-core cable).
🧠 Exam Technique: Easy Recall Mnemonics
- Brown = Bottom Right (Live).
- Blue = Bottom Left (Neutral).
- Striped Green and Yellow = Goes to the top (Earth).
- Note: Plastic kettles have double insulation, meaning they only require a 2-core cable (Live & Neutral, no Earth wire needed).
Linking Current, Potential Difference, and Power
Equation Recall
✅ Correct Equation
power = potential difference × current
or
P = V I
❌ Common Errors
- Writing incorrect letters such as C for current (current must be I).
- Writing division instead of multiplication (e.g., P = V / I).
- Writing units instead of quantities (e.g., Watts = Volts × Amps does not get full credit when physical quantities are asked for).
Calculating Current in the Heating Element
Calculation & Significant Figures
📐 Step-by-Step Calculation
Power P = 2100 W
Potential difference V = 230 V
2100 = 230 × I
I = 2100 / 230
I = 9.1304... A
I = 9.1 A
🧠 Exam Technique: Significant Figures Trap
Notice the explicit instruction: "Give your answer to 2 significant figures."
- 1st sig fig: 9
- 2nd sig fig: 1
- The next digit is 3 (less than 5), so round down to 9.1.
- Even if an arithmetic mistake was made earlier, you can still gain the final mark if your wrong answer is correctly rounded to 2 sig figs!
Specific Latent Heat of Vaporisation
Equation Sheet Application
📐 Step-by-Step Calculation
Thermal energy for a change of state = mass × specific latent heat
E = m × L
Energy E = 18 000 J , Mass m = 0.0080 kg
18 000 = 0.0080 × L
L = 18 000 / 0.0080
L = 2 250 000 J/kg
(2.25 × 10⁶ J/kg or rounded to 2 300 000 J/kg also accepted)
❌ Common Errors
- Using the specific heat capacity formula ( E = m c Δθ ) instead of latent heat. Remember: boiling/changing state occurs at constant temperature, so use E = m L .
- Dividing upside down: doing 0.0080 / 18 000 .
- Miscounting zeroes when entering small decimals on the calculator.
Calculating Appliance Efficiency
Ratio & Percentage
📐 Step-by-Step Calculation
efficiency = useful output energy transfer / total input energy transfer
efficiency = 75 600 / 84 000
Decimal form: 0.9
OR as a percentage: 90%
🧠 Exam Technique
- Efficiency has NO units if written as a decimal (0.9). Do not write "0.9 J" or "0.9 W".
- Efficiency must always be less than 1 (or less than 100%). If your answer is greater than 1, you divided total input by useful output!
Advantages of High Efficiency
Explanation & Reasoning
✅ Model Answer
Point 1 (Cause): Less energy is wasted (transferred to non-useful stores like the surrounding air). [1 Mark]
Point 2 (Consequence): Therefore, it costs less money to run OR it uses less electricity. [1 Mark]
• Allow "less power wasted".
• Allow "appliance is used for less time / heats up faster".
❌ Common Errors & Examiner Tips
- Too vague: Stating just "it's better for the environment" without explaining why (e.g. less electricity needed means fewer fossil fuels burned).
- Vague cost remarks: Saying "it is cheaper" without clarifying whether you mean purchase price or running cost. High efficiency appliances often cost more to buy, but less to run!
Topics
Physics · P1: Energy · P2: Electricity · P3: Particle Model of Matter
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.