AQA GCSE Physics Physics Paper 1 (Foundation), November 2020: Question 7
18 marks · Standard Demand difficulty · Extended Answer
Investigate specific heat capacity, circuit components, electrical power, heating curves, and thermal energy calculations using an electric kettle.
Practise this questionQuestion
Question text
07 A student heated water in an electric kettle.
07.1 Water has a high specific heat capacity.
Complete the sentence.
Choose answers from the box.
[2 marks]
°C J kg s W
The specific heat capacity of a substance is the energy needed to raise the
temperature of 1 of the substance by 1 .
07.2 The kettle circuit contains a thermistor which is used to switch the kettle off when the
water reaches 100 °C.
What is the correct symbol for a thermistor?
[1 mark]
Tick ( ) one box.
07.3 The resistance of the heating element in the kettle is 15 Ω.
The current in the heating element is 12 A.
Calculate the power of the heating element.
Use the equation:
power = (current)2 × resistance
[2 marks]
Power = W
The student investigated how quickly the kettle could increase the temperature of
0.50 kg of water.
Figure 10 shows the results of the investigation.
Figure 10
07.4 The temperature of the water did not start to increase until 10 seconds after the kettle
was switched on.
What is the reason for this?
[1 mark]
Tick ( ) one box.
Energy is transferred from the surroundings to the kettle.
The charge flows slowly through the kettle circuit.
The heating element in the kettle takes time to heat up.
The power output of the kettle increases slowly.
07.5 Describe a method the student could have used to obtain the results shown in
Figure 10.
[6 marks]
07.6 The mass of water in the kettle was 0.50 kg.
The temperature of the water increased from 20 °C to 100 °C.
specific heat capacity of water = 4200 J/kg °C
*27* Calculate the energy transferred to the water.
Use the Physics Equations Sheet.
[3 marks]
Energy = J
07.7 The water in the kettle boiled for a short time before the kettle switched off.
During this time 5.0 g of water changed to steam.
specific latent heat of vaporisation of water = 2260000 J/kg
Calculate the energy transferred to change the water to steam.
Use the Physics Equations Sheet.
[3 marks]
Energy = J
Mark scheme
Show the mark scheme
Question 7
AO /
Question Answers Extra information Mark
Spec. Ref.
07.1 kg allow kilogram 1 AO1
4.1.1.3
°C allow degrees Celsius 1 RPA 1
07.2 AO1
1 4.2.1.1
RPA 1
07.3 AO2
P = 122 × 15 1 4.2.4.1
RPA 1
P = 2160 (W) 1
07.4 The heating element in the 1 AO1
kettle takes time to heat up 4.1.1.1
RPA 1
07.5 Level 3: The method would lead to the production of a valid AO1
5–6
outcome. All key steps are identified and logically sequenced. 4.1.1.1
RPA 1
Level 2: The method would not necessarily lead to a valid
outcome. Most steps are identified, but the method is not fully 3–4
logically sequenced
Level 1: The method would not lead to a valid outcome. Some
1–2
relevant steps are identified, but links are not made clear.
No relevant content 0
Indicative content:
• measure the mass of water using a balance
or
measure the volume of water using a measuring cylinder
• measure the initial temperature of the water
• pour the water into the kettle
• put temperature probe in the water
or
put a thermometer in the water
• switch kettle on
• record temperature
• measure time with a stopclock
• use an interval of 5 seconds
Question Answers Extra information Mark AO /
Spec. Ref.
07.6 AO2
Δϴ = 80 (°C) 1 4.1.1.3
RPA 1
E = 0.50 × 4200 × 80 allow E = 0.50 × 4200 × their 1
value of Δϴ
E = 168 000 (J) allow an answer consistent with 1
their value of Δϴ
07.7 AO2
m = 0.005 (kg) 1
4.3.2.3
E = 0.005 × 2 260 000 this mark may score if m is 1
not/incorrectly converted
allow an answer consistent with
E = 11 300 (J) 1
their value of m
Total 18
How to answer it
Energy Changes, Circuits, and Specific Heat Capacity in an Electric Kettle
What this question tests
This multi-part question assesses core electricity and energy concepts through the context of an electric kettle. Key skills include recalling the definition of specific heat capacity, identifying standard circuit component symbols (thermistor), applying electrical power equations, describing a required practical method for heating water, and calculating thermal energy changes using specific heat capacity and specific latent heat equations.
Specific Heat Capacity Definition Units
✅ Correct Answers
- First gap: kg (or kilogram)
- Second gap: °C (or degrees Celsius)
💡 Key Knowledge
Specific heat capacity is defined as the amount of energy needed to raise the temperature of 1 kg of a substance by 1 °C (or 1 K).
Thermistor Circuit Symbol
✅ Correct Answers
The first symbol (a resistor box with a diagonal line cutting through it representing temperature dependence).
❌ Common Errors
Students often confuse the thermistor symbol with a Light Dependent Resistor (LDR), which features arrows pointing towards a boxed circle, or a standard fixed resistor.
Calculating Electrical Power
📐 Step-by-Step Calculation
- State equation: power = (current)² × resistance
- Substitute values: P = 12² × 15
- Calculate: P = 144 × 15 = 2160 W
🧠 Exam Technique
Always show your substitution step clearly before writing the final calculated value. Even if arithmetic slips occur, substitution marks can protect your score.
Interpreting Heating Delay
✅ Correct Answer
The heating element in the kettle takes time to heat up.
💡 Examiner Insight
At the start of practical investigations involving electrical heaters, thermal energy must first transfer into the metal element itself before it can effectively transfer into the surrounding water.
Describing a Practical Method
🧠 Level of Response Strategy (6-Mark Question)
- Measure mass/volume: Use a balance to measure 0.50 kg of water (or measuring cylinder).
- Initial reading: Measure and record the initial temperature using a thermometer or temperature probe.
- Setup: Pour water into the kettle, switch it on, and simultaneously start a stopclock.
- Data collection: Record the temperature at regular time intervals (e.g., every 5 or 10 seconds) until reaching 100 °C.
❌ Common Errors
Students lose marks here by failing to link timing with temperature taking, or by omitting the initial temperature measurement before turning the appliance on.
Calculating Thermal Energy Transferred
📐 Step-by-Step Calculation
- Find temperature change (Delta Theta): 100 - 20 = 80 °C
- State equation: Energy = mass × specific heat capacity × temperature change ( E = m c Delta Theta )
- Substitute values: E = 0.50 × 4200 × 80
- Calculate final answer: E = 168 000 J
❌ Common Calculation Traps
Watch out for incorrect temperature difference calculations. Always do final temperature minus initial temperature.
Calculating Latent Heat Energy
📐 Step-by-Step Calculation
- Convert mass to kg: 5.0 g = 5.0 / 1000 = 0.005 kg
- State equation: Energy = mass × specific latent heat ( E = m L )
- Substitute values: E = 0.005 × 2 260 000
- Calculate final answer: E = 11 300 J
❌ Common Calculation Traps
Forgetting to convert grams into kilograms (dividing by 1000) is the single most frequent reason students drop marks in latent heat calculations.
Topics
Physics · Required Practicals · P1: Energy · P2: Electricity · P3: Particle Model of Matter · Required Practicals
Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 1 (Foundation), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.