4.1 Energy — 8463 revision notes

4.1.1.1

Energy stores and systems

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

A system is an object or group of objects. When a system changes, the way energy is stored changes: energy is transferred out of one store (for example the gravitational potential energy store of a raised object) and into another (its kinetic energy store), and the total energy of a closed system stays constant.

Explanation

A system is one object or a group of objects being considered. When a system changes, energy is transferred between its stores or between the system and its surroundings.
Describe the change by naming the store that decreases, the store that increases and the transfer pathway: mechanically, electrically, by heating or by radiation.
Energy stores include kinetic, thermal, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear.
Total energy is conserved, so increases in stores equal the decrease elsewhere.
Energy is not used up; it may become dissipated into less useful thermal stores.

Worked example

A child on a trampoline is stationary at the top of a bounce, position A. The child falls and is again stationary at the lowest point, position B, where the trampoline is stretched the most. Describe the energy transfers as the child moves from position A to position B.

[3 marks]

Total for this question: 3

1.In position A the child has energy in a gravitational potential energy store (the child is at rest, so there is no kinetic energy).
2.As the child moves down, energy is transferred mechanically from the gravitational potential energy store to the child's kinetic energy store, and then to the elastic potential energy store of the trampoline as it stretches.
3.In position B the child is at rest and the trampoline is fully stretched, so all the energy is in the elastic potential energy store (a small amount is dissipated to thermal stores of the air and trampoline).

Answer: Gravitational potential energy store (A) → kinetic energy store → elastic potential energy store of the trampoline (B). Name each store and say which decreases and which increases.

Common mistakes

Don't fall into the trap of saying the load gains ‘electrical energy’ instead of naming its gravitational potential energy store.
Don't fall into the trap of claiming energy is used up rather than transferred or dissipated.
Don't fall into the trap of naming stores but omitting the transfer pathway between them.

Mark-scheme wording to use

“group of objects that interact” — AQA 8463, June 2018 Paper 2H, Q01.3
“all the energy is elastic potential energy” — AQA 8463, June 2023 Paper 1H, Q07.2
“energy is transferred to the surroundings” — AQA 8463, June 2022 Paper 1F, Q01.5
“total energy of ball and Earth / ground is constant … allow ‘a system’ for ball and Earth … allow energy is conserved” — AQA 8463, June 2018 Paper 2H, Q01.4

What the examiner wants

Name the store, not the pathway, when asked which store increases: 'thermal energy store', never 'heat'. For a 'describe the energy transfers' question the marks are one per store in sequence, and a lower rebound only scores when you say where the missing energy went — to the surroundings, so the total energy of the system is unchanged.

Exam tip

For ‘describe the energy changes’, name the decreasing store, transfer pathway and increasing store.

Tier 1 · Easy

ORIGINAL

A wheeled toy is given a push across a level floor and gradually stops. Describe the main energy-store changes after it is released.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

An electrically powered hotplate transfers

96\,\text{kJ}

of energy. The pan's thermal energy store increases by

61\,\text{kJ}

and the food's thermal energy store increases by

27\,\text{kJ}

. Calculate the energy transferred to other stores and state where it is likely to be stored.

[3 marks]

Total for this question: 3

Tier 3 · Hard

ORIGINAL

A model launcher begins with

240\,\text{J}

in its elastic potential energy store. After the model has left the launcher, the spring is fully relaxed. The model has

150\,\text{J}

in its kinetic energy store and

54\,\text{J}

in its gravitational potential energy store; these and the thermal stores account for the whole system. Calculate the energy in thermal stores and describe the complete redistribution.

[4 marks]

Total for this question: 4

4.1.1.2

Changes in energy

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

The energy in a moving object's kinetic store is $E_k=\dfrac{1}{2}mv^2$ ; in a stretched spring's elastic potential store, $E_e=\dfrac{1}{2}ke^2$ (below the limit of proportionality); and in the gravitational potential store of an object raised through a height $h$ , $E_p=mgh$ . Energies are in joules when mass is in kg, speed in m/s, spring constant in N/m, extension and height in m and $g$ in N/kg.

Explanation

Calculate energy in kinetic, elastic potential and gravitational potential stores using $E_k=\dfrac{1}{2}mv^2$ , $E_e=\dfrac{1}{2}ke^2$ and $E_p=mgh$ .
Use kilograms, metres per second, newtons per metre, metres and the supplied value of $g$ .
The elastic equation applies while the spring obeys the linear force–extension relationship, and $e$ is extension rather than total length.
If a question states that transfers are complete with no dissipation, equate the decrease in one store to the increase in another.
Speed and extension are squared, so doubling either makes the corresponding energy four times larger.

Worked example

A toy launcher contains a spring with a spring constant of

80\,\text{N/m}

. The spring is compressed by

0.060\,\text{m}

. When the spring is released, all of the energy stored in the spring is transferred to the kinetic energy store of a ball of mass

0.045\,\text{kg}

. Calculate the speed of the ball as it leaves the launcher. Give your answer to 2 significant figures.

[6 marks]

Total for this question: 6

1.Elastic potential energy stored: $E_e=\dfrac{1}{2}ke^2=0.5\times80\times0.060^2$ .
2. $E_e=0.144\,\text{J}$ (extension squared: $0.060^2=0.0036$ ).
3.Equate to kinetic energy: $0.144=0.5\times0.045\times v^2$ .
4.Rearrange: $v^2=\dfrac{0.144}{0.5\times0.045}=6.4$ .
5. $v=\sqrt{6.4}=2.529\ldots\,\text{m/s}$ .
6.To 2 significant figures, $v=2.5\,\text{m/s}$ .

Answer: $v=2.5\,\text{m/s}$ (2 significant figures)

Common mistakes

Don't fall into the trap of using $E_k=mv/2$ and failing to square the speed.
Don't fall into the trap of using the spring's total length instead of its extension in $E_e=\frac12ke^2$ .
Don't fall into the trap of using a mass in grams rather than kilograms.

Mark-scheme wording to use

“kinetic energy = 0.5 × mass × speed²” — AQA 8463, November 2021 Paper 1F, Q07.2
stretched length minus original length — paraphrase of AQA 8463, June 2024 Paper 1F, Q03.1
energy transferred to surroundings … work done against air resistance — paraphrase of AQA 8463, June 2024 Paper 1F, Q03.6
v = 2.6 m/s to 2 significant figures — paraphrase of AQA 8463, June 2025 Paper 1H, Q10.1

What the examiner wants

The June 2025 Paper 1H report identified failure to square the extension as the main calculation error on the spring-to-speed question. Write the substitution with the square shown ( $0.5\times k\times e^2$ ), keep the unrounded value until the last line, and round only when the question asks — the final mark is often for the significant figures.

Exam tip

Write the correct store equation and convert every quantity to SI units before substitution.

Tier 1 · Easy

ORIGINAL

Calculate the kinetic energy of a

2.0\,\text{kg}

cart moving at

3.0\,\text{m/s}

.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

A

35\,\text{kg}

climber gains

4.2\,\text{m}

in vertical height. Calculate the increase in the climber's gravitational potential energy store. Use

g=9.8\,\text{N/kg}

.

[2 marks]

Total for this question: 2

Tier 3 · Hard

ORIGINAL

A spring of spring constant

320\,\text{N/m}

is compressed by

0.15\,\text{m}

. It launches a

0.45\,\text{kg}

cart on a level frictionless track. Calculate the cart's launch speed.

[4 marks]

Total for this question: 4

4.1.1.3

Energy changes in systems

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius. The energy stored in or released from a system as its temperature changes is $\Delta E=mc\Delta\theta$ : change in thermal energy (J) = mass (kg) × specific heat capacity ( $\text{J/kg}\,^{\circ}\text{C}$ ) × temperature change ( $^{\circ}\text{C}$ ).

Explanation

Specific heat capacity is the energy required to raise the temperature of $1\,\text{kg}$ of a substance by $1\,{}^\circ\text{C}$ .
Use $\Delta E=mc\Delta\theta$ , where energy is in joules, mass in kilograms, specific heat capacity in $\text{J/(kg }{}^\circ\text{C)}$ and temperature change in degrees Celsius.
In the required practical, measure mass, supply energy with an electrical heater using $E=Pt$ , and record the temperature rise.
Insulate the block, ensure good thermal contact and repeat readings because energy transferred to the surroundings otherwise makes the calculated value inaccurate.

Required practical 1: an immersion heater and thermometer sit in holes in an insulated metal block; the energy supplied is read from a joulemeter, or from

E=VIt

.

Worked example

An immersion heater transfers

5400\,\text{J}

of energy to a

0.50\,\text{kg}

block of aluminium. The specific heat capacity of aluminium is

900\,\text{J/kg}\,^{\circ}\text{C}

. Calculate the temperature rise of the block.

[3 marks]

Total for this question: 3

1.Substitute into $\Delta E=mc\Delta\theta$ : $5400=0.50\times900\times\Delta\theta$ .
2.Rearrange: $\Delta\theta=\dfrac{5400}{0.50\times900}=\dfrac{5400}{450}$ .
3. $\Delta\theta=12\,^{\circ}\text{C}$ .

Answer: $\Delta\theta=12\,^{\circ}\text{C}$

Required practical 1

Determining the specific heat capacity of a material by linking the energy transferred to its temperature rise

Apparatus

Metal block (e.g. aluminium or iron) with two holes, one for the heater and one for the thermometer
Immersion heater and low-voltage power supply
Joulemeter, or an ammeter, voltmeter and stopwatch to give $E=VIt$
Thermometer (a drop of oil in its hole improves thermal contact)
Balance, and insulation to wrap the block

Method

Measure the mass of the block on a balance and record it in kilograms.
Wrap the block in insulation, insert the heater and thermometer, and record the starting temperature.
Switch on the heater and start the stopwatch; record the joulemeter reading (or $V$ and $I$ ) and the temperature every minute.
After about ten minutes switch off, but keep watching the thermometer and record the highest temperature reached.
Plot temperature against energy transferred; the gradient of the straight part is $1/(mc)$ , so $c=1/(m\times\text{gradient})$ .

Variables

Independent:: energy transferred to the block (set by the heating time)
Dependent:: temperature of the block
Control:: mass and material of the block; heater power (same supply voltage); insulation and starting temperature

Hazards and precautions

The heater and block become hot enough to burn: do not touch them until they have cooled, and stand the block on a heatproof mat.
Keep water and oil away from the electrical supply; switch off at the supply before adjusting the circuit.

Common mistakes

Don't fall into the trap of substituting the final temperature instead of final minus initial temperature.
Don't fall into the trap of using mass in grams in the specific heat capacity equation.
Don't fall into the trap of assuming all heater energy reaches the block despite heating the surroundings.

Mark-scheme wording to use

“the calculated specific heat capacity will be more accurate … the iron block will transfer thermal energy to the surroundings at a lower rate” — AQA 8463, June 2023 Paper 1H, Q02.3
“so the thermometer temperature was the same as the temperature of the iron block” — AQA 8463, June 2023 Paper 1H, Q02.1
“insulate the beaker … or add a lid” — AQA 8463, June 2025 Paper 1H, Q02.3

What the examiner wants

The June 2025 Paper 1H report stressed that Level 3 on the method question required a clear determination of the mass of water (weigh the beaker empty and full, subtract), and that 4.76% was not the required percentage difference: the difference between the measured and true values is divided by the true value ( $210/4200=5\%$ ), not by the measured one.

Exam tip

In a practical evaluation, identify heat loss as making the calculated specific heat capacity too high.

Tier 1 · Easy

ORIGINAL

State what a specific heat capacity of

900\,\text{J/(kg}\,{}^\circ\text{C)}

means.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

A

1.5\,\text{kg}

stone block has specific heat capacity

900\,\text{J/(kg}\,{}^\circ\text{C)}

. Calculate the change in its thermal energy store when its temperature rises by

28\,{}^\circ\text{C}

.

[2 marks]

Total for this question: 2

Tier 3 · Hard

ORIGINAL

A

75\,\text{W}

heater warms a

0.30\,\text{kg}

sample for

6.0\,\text{minutes}

. The sample's temperature rises by

32\,{}^\circ\text{C}

and

80\%

of the electrical energy is transferred to its thermal energy store. Determine the sample's specific heat capacity.

[5 marks]

Total for this question: 5

4.1.1.4

Power

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

Power is the rate at which energy is transferred or the rate at which work is done: $P=\dfrac{E}{t}$ and $P=\dfrac{W}{t}$ , with power in watts (W), energy transferred or work done in joules (J) and time in seconds (s). An energy transfer of 1 joule per second is a power of 1 watt.

Explanation

Power is the rate of energy transfer or the rate of doing work. Use $P=E/t$ or $P=W/t$ , with energy or work in joules and time in seconds, to obtain power in watts.
One watt means one joule transferred each second.
Two devices can transfer the same amount of energy but have different powers: the device that completes the transfer in less time has greater power.
Conversely, two devices operating for the same time transfer different energies if their powers differ.
Power is a rate, not an energy store or a total amount of energy.

Worked example

A student of mass

55\,\text{kg}

runs up a flight of stairs with a vertical height of

3.2\,\text{m}

in a time of

4.0\,\text{s}

. Gravitational field strength

=9.8\,\text{N/kg}

. Calculate the student's power output associated with the increase in gravitational potential energy. Give your answer to 2 significant figures.

[4 marks]

Total for this question: 4

1.Gravitational potential energy gained: $E_p=mgh=55\times9.8\times3.2$ .
2. $E_p=1724.8\,\text{J}$ (keep the unrounded value).
3.Power: $P=\dfrac{E}{t}=\dfrac{1724.8}{4.0}=431.2\,\text{W}$ .
4.To 2 significant figures, $P=430\,\text{W}$ .

Answer: $P=430\,\text{W}$ (2 significant figures)

Common mistakes

Don't fall into the trap of giving power in joules rather than watts.
Don't fall into the trap of multiplying energy by time instead of dividing by time.
Don't fall into the trap of saying a more powerful device always transfers more energy without considering duration.

Mark-scheme wording to use

“power = energy transferred / time … or P = E/t” — AQA 8463, June 2025 Paper 1F, Q02.4
kinetic energy also increases … energy dissipated in muscles or transferred thermally to surroundings — paraphrase of AQA 8463, June 2022 Paper 1H, Q09.2
boy's mass is greater than the girl's — paraphrase of AQA 8463, June 2022 Paper 1H, Q09.3

What the examiner wants

Convert before you substitute: kilowatts to watts, minutes to seconds. The June 2025 Paper 1H report identified failure to convert 30 minutes as the main error on a power–energy question, and AQA's schemes give the conversion its own mark ('3 kW = 3000 W'). When two people have the same power but different times, argue through $E=Pt$ : the same power for longer means more energy, so a greater mass was lifted.

Exam tip

When comparing devices, state that the more powerful one transfers energy faster.

Tier 1 · Easy

ORIGINAL

A small motor transfers

600\,\text{J}

of energy in

20\,\text{s}

. Calculate its power.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

Winch A and winch B each do

18\,\text{kJ}

of work. A takes

30\,\text{s}

and B takes

45\,\text{s}

. Calculate both powers and compare them.

[4 marks]

Total for this question: 4

Tier 3 · Hard

ORIGINAL

A hoist raises a

250\,\text{kg}

load through

12\,\text{m}

in

25\,\text{s}

. Calculate the useful power of the hoist. Use

g=9.8\,\text{N/kg}

. A second hoist performs the same lift in

18\,\text{s}

; calculate its useful power.

[5 marks]

Total for this question: 5

4.1.2.1

Energy transfers in a system

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed. In a closed system there is no net change to the total energy. In every system change some energy is dissipated — stored in less useful ways, usually as thermal energy of the surroundings — and this is what is meant by energy being 'wasted'.

Explanation

Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed. In a closed system, the total energy does not change.
Dissipated energy spreads into thermal stores of the surroundings and becomes less useful, rather than disappearing.
Reduce unwanted mechanical transfers with lubrication, which lowers friction.
Reduce transfer by heating with thermal insulation, including thicker walls and materials that trap air.
A material with a high thermal conductivity transfers energy through it rapidly; increasing wall thickness reduces the transfer rate for the same material and temperature difference.

Worked example

Two identical cans of hot water are each wrapped in the same thickness of a different material, X or Y. The water in the can wrapped in X cools from

85\,^{\circ}\text{C}

to

65\,^{\circ}\text{C}

in

6.0

minutes. The water in the can wrapped in Y takes

10.0

minutes to cool through the same temperature change. Explain which material has the higher thermal conductivity.

[2 marks]

Total for this question: 2

1.The same temperature decrease of $20\,^{\circ}\text{C}$ happens in a shorter time for X, so the same amount of energy leaves the can in less time.
2.A higher rate of energy transfer through the wrapping means X has the higher thermal conductivity (Y is the better insulator).

Answer: X — the same temperature decrease in a shorter time means the rate of energy transfer is higher, so X's thermal conductivity is higher.

Required practical 2

Investigating the effectiveness of different materials as thermal insulators (physics only)

Apparatus

Small beaker or metal can with a lid, and a larger beaker to hold the insulation around it
Insulating materials of equal thickness (e.g. bubble wrap, cotton wool, newspaper, foam)
Kettle, measuring cylinder, thermometer and stopwatch

Method

Measure a fixed volume of hot water (e.g. $80\,\text{cm}^3$ ) into the inner beaker and fit the lid with the thermometer through it.
Record the starting temperature, then the temperature every minute for ten minutes.
Repeat with each insulating material in turn, keeping the volume, starting temperature and thickness of insulation the same.
To test thickness, repeat with the same material in one, two, three and four layers.
Plot temperature against time for each material; the shallowest curve (smallest temperature drop) is the best insulator.

Variables

Independent:: type of insulating material (or, in the second part, its thickness)
Dependent:: temperature of the water after a fixed time (or the time for a fixed temperature drop)
Control:: volume of water; starting temperature; thickness of insulation and use of a lid

Hazards and precautions

Hot water can scald: carry the kettle and beaker carefully, keep the apparatus away from the edge of the bench, and do not exceed the beaker's capacity.
A glass thermometer can break: hold it by the top and never use it to stir.

Common mistakes

Don't fall into the trap of saying dissipated energy has been destroyed.
Don't fall into the trap of claiming a high thermal conductivity makes a material a good insulator.
Don't fall into the trap of suggesting lubrication reduces unwanted heating without linking it to reduced friction.

Mark-scheme wording to use

the same temperature decrease in a shorter time means higher thermal conductivity — paraphrase of AQA 8463, June 2022 Paper 1H, Q04.5
total energy of track and car is constant — paraphrase of AQA 8463, November 2021 Paper 1H, Q08.1
“energy becomes less useful” — AQA 8463, November 2021 Paper 1F, Q06.5
lower rate of cooling — paraphrase of AQA 8463, June 2022 Paper 1F, Q08.6

What the examiner wants

Say 'rate'. Insulation lowers the rate of energy transfer to the surroundings; it does not stop it. In the insulation practical the independent variable is the type of material (AQA's scheme adds 'not thickness' when thickness was held constant), the dependent variable is the temperature after a fixed time or the time for a fixed drop, and a closed system is one whose total energy is constant.

Exam tip

For an insulation explanation, name the transfer being reduced and the property or design feature that reduces its rate.

Tier 1 · Easy

ORIGINAL

Explain why adding oil to the axle of a turning wheel reduces unwanted energy transfers.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

Wall X is twice as thick as wall Y and both are made from the same material. Explain which wall gives the lower rate of energy transfer by conduction. Then state how replacing the material with one of lower thermal conductivity affects the rate.

[3 marks]

Total for this question: 3

Tier 3 · Hard

ORIGINAL

Plan an investigation to compare the effectiveness of three fabrics as thermal insulators around identical beakers of hot water. Include the measurements, control variables and how the results should be used.

[6 marks]

Total for this question: 6

4.1.2.2

Efficiency

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

Efficiency is the fraction (or percentage) of the input energy that is transferred usefully: $\text{efficiency}=\dfrac{\text{useful output energy transfer}}{\text{total input energy transfer}}$ , or equivalently $\dfrac{\text{useful power output}}{\text{total power input}}$ . It has no unit, can never exceed 1 (100%), and is raised by reducing unwanted transfers — lubrication against friction, thermal insulation against heating of the surroundings.

Explanation

Efficiency is the fraction of total input energy transferred usefully: $\text{efficiency}=\dfrac{\text{useful output energy}}{\text{total input energy}}$ .
The same ratio can use useful power output and total power input.
A decimal efficiency lies between $0$ and $1$ ; multiply by $100$ only when a percentage is required.
If efficiency is $0.72$ , then $72\%$ of the input is useful and $28\%$ is dissipated.
Higher tier: AQA restricts "describe ways to increase the efficiency of an intended energy transfer" to Higher tier; typical ways are lubrication to reduce friction and thermal insulation to reduce heating of the surroundings.

A Sankey-style energy transfer showing useful output and dissipated energy.

Worked example

An electric motor has an efficiency of

0.60

. The motor transfers

2.4\,\text{J}

of energy usefully when it lifts a load. Calculate the total input energy transfer to the motor.

[3 marks]

Total for this question: 3

1.Substitute into $\text{efficiency}=\dfrac{\text{useful output energy transfer}}{\text{total input energy transfer}}$ : $0.60=\dfrac{2.4}{\text{total input}}$ .
2.Rearrange: $\text{total input}=\dfrac{2.4}{0.60}$ .
3. $\text{total input energy transfer}=4.0\,\text{J}$ (so $1.6\,\text{J}$ is dissipated, mainly by heating the surroundings).

Answer: $4.0\,\text{J}$

Common mistakes

Don't fall into the trap of dividing total input by useful output and obtaining an efficiency above $100\%$ .
Don't fall into the trap of multiplying by $100$ when the question requests a decimal efficiency.
Don't fall into the trap of mixing useful energy with total power in the same ratio.

Mark-scheme wording to use

“efficiency = useful output energy transfer / total input energy transfer” — AQA 8463, June 2025 Paper 1F, Q07.3
efficiency increases … useful-energy proportion increases or wasted-energy proportion decreases … less work against friction — paraphrase of AQA 8463, June 2022 Paper 1F, Q09.3
greater percentage usefully transferred by A; A takes less time to boil the same volume — paraphrase of AQA 8463, June 2025 Paper 1F, Q05.5

What the examiner wants

An efficiency explanation is a chain, not a label: name the unwanted transfer (work done against friction, energy transferred by heating to the surroundings), say it is reduced, then say the useful proportion is greater. AQA's June 2024 Paper 1H scheme explicitly ignores 'energy is wasted' on its own; an answer above 1 or 100% is wrong before you check anything else.

Exam tip

Check that an ordinary device's efficiency is no greater than $1$ or $100\%$ .

Tier 1 · Easy

ORIGINAL

A device receives

90\,\text{J}

and transfers

72\,\text{J}

usefully. Calculate its efficiency as a decimal and as a percentage.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

A pump has a total power input of

560\,\text{W}

and a useful power output of

420\,\text{W}

. Calculate its efficiency and its wasted power.

[3 marks]

Total for this question: 3

Tier 3 · Hard

ORIGINAL

Higher only: A motor transfers

80\%

of its input energy to a rotating shaft. A generator then transfers

65\%

of the shaft energy to electrical energy. Calculate the overall efficiency and the useful electrical energy produced from an initial input of

250\,\text{kJ}

. Suggest one change that could increase the efficiency of this intended transfer and explain how it helps.

[6 marks]

Total for this question: 6

4.1.3

National and global energy resources

Notes

Evidence from your answers: none yet

Your confidence:

A self-report of how sure you feel. It does not measure mastery. Evidence from your answers reaches secure after the latest Tier 2/3 attempt is correct, with three correct distinct drills across at least two dates and two practice sources.

Definition

A renewable energy resource is one that is being, or can be, replenished as it is used: bio-fuel, wind, hydro-electricity, geothermal, the tides, the Sun and water waves. Fossil fuels (coal, oil and gas) and nuclear fuel are non-renewable — finite resources. Energy resources are used for transport, electricity generation and heating.

Explanation

Renewable resources are replenished as they are used: biofuel, wind, hydroelectricity, geothermal, tides, sunlight and water waves. Fossil fuels and nuclear fuel are non-renewable.
Compare resources for transport, heating and electricity generation using reliability, response to demand, environmental effects and cost.
Wind and solar output vary with conditions, while fossil-fuel stations can respond to demand but release greenhouse gases and pollutants.
Nuclear generation has low operational carbon emissions but produces radioactive waste.
Patterns of use reflect availability, technology, economics and political, social or ethical choices; science identifies impacts but does not make every decision.

Worked example

A town is deciding whether to build a wind farm or a gas-fired power station to generate electricity. Compare the two energy resources. Your answer should include the reliability of each resource and its environmental impact.

[4 marks]

Total for this question: 4

1.Renewability: wind is a renewable resource, replenished as it is used; natural gas is a non-renewable fossil fuel with a finite supply.
2.Environmental impact: burning gas releases carbon dioxide, which causes global warming; wind turbines emit no carbon dioxide while operating, though they take up land and some people object to their appearance and noise.
3.Reliability and demand: the power output of wind turbines is unpredictable and can be zero on a still day, whereas a gas-fired station can run continuously and its output can be increased quickly when demand rises.
4.Conclusion: a justified choice against the same criteria — for example, the wind farm for low emissions, with the gas station able to cover periods of low wind.

Answer: Level 2 (3–4 marks) needs both resources compared on the same criteria — renewable vs non-renewable, carbon dioxide and global warming, reliability of output — with a conclusion.

Common mistakes

Don't fall into the trap of calling nuclear fuel renewable because its operational carbon emissions are low.
Don't fall into the trap of claiming wind power is completely reliable because wind is free.
Don't fall into the trap of giving only one advantage without comparing the same criterion for both resources.

Mark-scheme wording to use

“renewable … an energy resource that is replenished as it is used” — AQA 8463, June 2025 Paper 1H, Q01.1
“non-renewable … an energy resource that is finite” — AQA 8463, June 2025 Paper 1H, Q01.1
burning gas releases carbon dioxide … this causes global warming — paraphrase of AQA 8463, November 2020 Paper 1F, Q01.3
“the power output of wind turbines is unpredictable” — AQA 8463, Specimen Paper 1F, Q01.4

What the examiner wants

The June 2025 Paper 1H report noted that 'renewable' required replenishment as it is used, not merely an infinite supply — AQA's scheme ignores 'infinite', 'not running out' and 'sustainable'. For an environmental effect, name the emission and then the linked consequence (carbon dioxide → global warming; sulfur dioxide → acid rain); 'pollution' on its own scores nothing.

Exam tip

For ‘compare’, discuss both resources against the same criteria and give a justified conclusion.

Tier 1 · Easy

ORIGINAL

Classify wind, natural gas, geothermal and nuclear fuel as renewable or non-renewable energy resources.

[2 marks]

Total for this question: 2

Tier 2 · Standard

ORIGINAL

In a region, the share of transport energy supplied by biofuel rises from

4\%

to

11\%

, while the share of heating energy supplied by oil falls from

38\%

to

25\%

. Describe both trends. Explain one environmental reason for the change and one practical reason why oil may still be used.

[4 marks]

Total for this question: 4

Tier 3 · Hard

ORIGINAL

A country is choosing between expanding offshore wind and building a nuclear power station. Evaluate the two options for large-scale electricity supply. Your answer should consider reliability, environmental impacts and economic or social factors.

[6 marks]

Total for this question: 6

Energy stores and systems

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

Changes in energy

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

Energy changes in systems

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

Power

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

Energy transfers in a system

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

Efficiency

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

National and global energy resources

Tier 1 · Easy

Tier 2 · Standard

Tier 3 · Hard

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