AQA GCSE Physics Physics Paper 1 (Higher), November 2020: Question 3
11 marks · Standard Demand difficulty · Short Answer
Calculate the mass and energy transferred in a hydroelectric power station and explain why it cannot meet peak electricity demand based on given data and graphs.
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Question text
03 Figure 4 shows a hydroelectric power station.
Figure 4
Electricity is generated when water from the reservoir flows through the turbines.
03.1 Write down the equation which links density (ρ), mass (m) and volume (V).
[1 mark]
03.2 The reservoir stores 6 500 000 m3 of water.
The density of the water is 998 kg/m3.
Calculate the mass of water in the reservoir.
Give your answer in standard form.
[4 marks]
Mass (in standard form) =11 kg
03.3 Write down the equation which links energy transferred (E), power (P) and time (t).
[1 mark]
03.4 The electrical generators can provide 1.5 × 109 W of power for a maximum of 5 hours.
Calculate the maximum energy that can be transferred by the electrical generators.
[3 marks]
Energy transferred = J
03.5 Figure 5 shows how the UK demand for electricity increases and decreases during
one day.
Figure 5
The hydroelectric power station in Figure 4 can provide 1.5 × 109 W of power for a
maximum of 5 hours.
Give two reasons why this hydroelectric power station is not able to meet the increase
in demand shown between 04:00 and 16:00 in Figure 5.
[2 marks]
*11* 1
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 mass 1 AO1
density =
volume 4.3.1.1
or
m
ρ =
V
03.2 AO2
m 1 4.3.1.1
998 =
6 500 000
m = 998 × 6 500 000 1
m = 6 487 000 000 1
m = 6.487 × 109 (kg) allow a correct conversion of 1
their calculated value of mass
into standard form
03.3 energy transferred = power × 1 AO1
time 4.2.4.2
or
E = Pt
03.4 AO2
t = 18 000 (s) 1 4.2.4.2
or
t = 5 × 60 × 60
E = 1.5 × 109 × 18 000 allow a correct substitution using 1
an incorrectly/not converted
value of t
E = 2.7 × 1013 (J) allow a correct calculation using 1
an incorrectly/not converted
value of t
03.5 the variation in demand is allow the increase in demand is 1 AO3
(much) greater than 1.5 × 109 W greater than the (power) output 4.1.3
of the (hydroelectric) power
station
demand remains high for longer allow 04:00 to 16:00 is 12 hours 1
than 5 hours allow 04:00 to 16:00 is greater
than 5 hours
Total 11
How to answer it
Energy Calculations & National Grid Demand
What this question tests
This question assesses your ability to recall and apply key physics equations relating density, mass, volume, power, energy, and time. It also tests your data-interpretation skills by asking you to analyze graphical electricity demand data against power station capabilities.
Density Equation Recall
✅ Correct Answer
density = mass / volume or ρ = m / V
💡 Key Knowledge
- Density is a measure of the compactness of a substance.
- Units: Density ( kg/m³ ), Mass ( kg ), Volume ( m³ ).
Calculating Mass in Standard Form
📐 Step-by-Step Calculation
- Rearrange the equation:
mass = density × volume ( m = ρ × V ) - Substitute the values:
m = 998 × 6 500 000 - Calculate raw value:
m = 6 487 000 000 kg - Convert to standard form:
6.487 × 10⁹ kg
❌ Common Errors
- Forgetting to convert the final answer into proper standard form ( A × 10ⁿ where 1 ≤ A < 10).
- Multiplying volume by density incorrectly due to poor equation rearrangement.
Energy and Power Equation Recall
✅ Correct Answer
energy transferred = power × time or E = P × t
🧠 Exam Technique
Always write out equations in standard letter symbols or full words as they appear on your equation sheet to guarantee marks.
Calculating Total Energy Transferred
📐 Step-by-Step Calculation
- Convert time into seconds:
5 hours = 5 × 60 × 60 = 18 000 s - Substitute into energy equation:
E = 1.5 × 10⁹ × 18 000 - Calculate final energy:
E = 2.7 × 10¹³ J
❌ Common Errors
- Unit Time Trap: Failing to convert hours into seconds, resulting in multiplying by 5 instead of 18,000. (Note: The mark scheme allows consequential working marks if time isn't converted, but getting it right secures full credit).
Interpreting National Demand Graphs
✅ Correct Answers (Any two of):
- The variation in demand is much greater than 1.5 × 10⁹ W (or greater than the power output of the power station).
- Demand remains high for longer than 5 hours (the graph shows high demand from 04:00 to 16:00, which is 12 hours).
🧠 Exam Technique
When questions ask for reasons based on a graph, always quote specific numbers or timeframes from the axes (e.g., comparing 12 hours of high demand to the 5-hour max generation limit) to anchor your points.
Topics
Physics · P1: Energy · P3: Particle Model of Matter · P2: Electricity
Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 1 (Higher), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.