AQA GCSE Physics Physics Paper 1 (Foundation), November 2020: Question 10
11 marks · Standard Demand difficulty · Short Answer
Calculate the mass and maximum energy transfer of a hydroelectric power station and explain why it cannot meet daily electricity demand variations.
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Question text
10 Figure 14 shows a hydroelectric power station.
Figure 14
Electricity is generated when water from the reservoir flows through the turbines.
10.1 Write down the equation which links density (ρ), mass (m) and volume (V).
[1 mark]
10.2 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) = kg
10.3 Write down the equation which links energy transferred (E), power (P) and time (t).
[1 mark]
10.4 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
10.5 Figure 15 shows how the UK demand for electricity increases and decreases during
one day.
Figure 15
The hydroelectric power station in Figure 14 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 15.
[2 marks]
Mark scheme
Show the mark scheme
Question 10
AO /
Question Answers Extra information Mark
Spec. Ref.
10.1 mass 1 AO1
density =
volume 4.3.1.1
or
m
ρ =
V
10.2 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
10.3 energy transferred = power × 1 AO1
time 4.2.4.2
or
E = Pt
10.4 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
10.5 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 Resources & Calculations Study Guide
What this question tests
This question assesses your ability to recall and apply core physics equations relating to density and energy transfer. It tests multi-step calculation skills, including standard form conversion, unit time conversions (hours to seconds), and the evaluation of national electricity demand data against power station capabilities.
Equation for Density
Write down the equation which links density, mass and volume.
✅ Correct Answer
density = mass / volume or ρ = m / V
💡 Key Knowledge
- Density is a measure of how compact a substance is.
- Units are typically kg/m³ for density, kg for mass, and m³ for volume.
Calculating Mass in Standard Form
The reservoir stores 6 500 000 m³ of water with a density of 998 kg/m³. Calculate the mass of water in standard form.
📐 Step-by-Step Calculation
- Rearrange equation: mass = density × volume ( m = ρ × V )
- Substitute values: m = 998 × 6 500 000
- Calculate initial value: m = 6 487 000 000 kg
- Convert to standard form: 6.487 × 10⁹ kg
❌ Common Errors
- Forgetting to convert the final answer into standard form, losing the final mark.
- Incorrectly counting decimal places when moving the decimal point (remember: 6.487 needs 9 jumps to the right).
Equation for Energy Transferred
Write down the equation which links energy transferred, power and time.
✅ Correct Answer
energy transferred = power × time or E = P × t
🧠 Exam Technique
Always learn equations with both their full words and standard scientific symbols. Both are accepted in GCSE mark schemes, but symbols are faster to write.
Calculating Maximum Energy Transferred
The generators provide 1.5 × 10⁹ W of power for a maximum of 5 hours. Calculate the maximum energy transferred.
📐 Step-by-Step Calculation
- Convert time to seconds: 5 hours × 60 minutes × 60 seconds = 18 000 s (or 5 × 3600)
- Substitute into energy equation: E = 1.5 × 10⁹ × 18 000
- Calculate final energy: 2.7 × 10¹³ J
❌ Common Errors
- The Time Trap: Multiplying power by 5 directly without converting hours into seconds. Power is measured in Watts (Joules per second), so time must always be in seconds!
Interpreting Data and Demand Graphs
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 15.
✅ Correct Answers (Any two of):
- The variation/increase in demand is much greater than 1.5 × 10⁹ W (the power output of the station).
- Demand remains high for longer than 5 hours (the time period is 12 hours from 04:00 to 16:00).
🧠 Exam Technique
Read graph axes carefully! Note that demand is given in × 10⁹ W , matching the power output units given in the stem. Always compare the numbers given in the text with the trends visible on the line graph.
Topics
Physics · P1: Energy · P3: Particle Model of Matter
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.