GCSE · AQA Combined Science · Paper 1 · P1 Energy

Energy, for the exam.

The whole of P1 — stores and transfers, the equations you have to recall, specific heat capacity, power, efficiency and energy resources. Built for both tiers.

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Both tiers in one booklet. Everything here is for Foundation and Higher. Anything that's Higher tier only sits in a purple HT box — Foundation students can skip those. Green boxes are required practicals. Do one topic at a time; each is about 10–15 minutes.

Topic 01 · 4.1.1.1 · Stores & systems

Energy stores and transfers

By the end of this topic you'll name the energy stores, describe how energy is transferred between them, and stop saying energy is "made" or "used up".

Part 1Energy is stored, then transferred

Energy is never created or destroyed — it just moves around. To talk about it clearly, physicists describe energy as sitting in stores. When something happens, energy is transferred from one store to another.

A system is just the object, or group of objects, you've decided to look at. When a system changes, you can describe the change as energy moving between stores.

The eight energy stores

Kinetic
Anything moving.
Thermal (internal)
The hotter something is, the more it has.
Chemical
In fuels, food and batteries — released by reactions.
Gravitational potential
Anything lifted up in a gravitational field.
Elastic potential
In stretched or squashed springs and bands.
Electrostatic / Magnetic / Nuclear
In separated charges, magnets, and atomic nuclei.

Energy is transferred in one of four ways. You need all four:

Mechanically — by a force doing work (pushing, pulling, stretching). Electrically — by a current doing work. By heating — from a hotter object to a cooler one. By radiation — carried away as waves, e.g. light or sound.

A FALLING BALL Gravitational store: FULL Kinetic store: empty Kinetic store: FULL Gravitational store: empty falls
As it falls: gravitational store → kinetic store

⚠ Watch out — the words examiners want

Energy is transferred between stores, never "created", "made", "used up" or "lost". Don't write "heat energy" — write "energy in the thermal store" or "transferred by heating". Don't write "sound energy" — sound is a way energy is transferred (by radiation), not a store.

Quick check

A battery-powered fan is switched on. Which describes the main transfer?

  • AElectrical store → kinetic store
  • BChemical store of the battery → kinetic store of the blades (transferred electrically)
  • CKinetic energy is created by the motor
  • DHeat energy → movement energy
Show answer
B. The store is the chemical store of the battery (there's no "electrical store"). It's transferred electrically by the current to the kinetic store of the blades. C and D use the banned words "created" and "heat energy".

Part 2Describing changes in a system

A common exam task: "Describe the energy transfers." Always say which store falls, which store rises, and how it was transferred.

Worked example — a car braking to a stop

A moving car brakes and stops. Describe the energy transfer.

BeforeEnergy is in the kinetic store of the car.
TransferFriction at the brakes does work — transferred mechanically, then by heating.
AfterEnergy is in the thermal store of the brakes & surroundings (dissipated).
Topic 1 — quick quiz
Click to reveal · 4 questions
  1. Name the four ways energy can be transferred.
    Mechanically (by a force), electrically (by a current), by heating, and by radiation.
  2. A child at the top of a slide slides down. Name the store that decreases and the store that increases.
    Gravitational potential store decreases; kinetic store increases (some is also dissipated to a thermal store by friction).
  3. Why is "the energy was lost" a poor answer?
    Energy can't be destroyed. It is dissipated — transferred to the surroundings (usually a thermal store) where it's spread out and no longer useful.
  4. A kettle boils water. State the store that empties, the store that fills, and how energy is transferred.
    Chemical/electrical supply → the thermal store of the water increases; energy is transferred electrically (then by heating within the water).
Topic 02 · 4.1.1.2 · KE & GPE

Kinetic & gravitational energy

Two equations you must recall — and the classic trick of swapping between them when something falls.

Part 1The two equations to recall

Equations

Ek = ½ m v² recall
kinetic energy (J) = ½ × mass (kg) × speed² (m/s)²
Ep = m g h recall
g.p.e. (J) = mass (kg) × gravitational field strength (N/kg) × height (m). Use g = 9.8 N/kg.

Worked example — kinetic energy of a car

A 1500 kg car travels at 20 m/s. Calculate its kinetic energy.

EquationEₖ = ½ m v²
Sub in= ½ × 1500 × 20² = ½ × 1500 × 400
Answer= 300 000 J (300 kJ)

⚠ Watch out — square the speed

It's v², not v. Square the speed before you multiply. And because of the square, doubling the speed quadruples the kinetic energy — that's why stopping distances grow so fast. Speed must be in m/s, not km/h.

DOUBLE THE SPEED → 4× THE KE speed v 1 unit speed 2v 4 units
Kinetic energy depends on speed squared

Part 2The falling-object trick

When something falls (and you ignore air resistance), the energy leaving the gravitational store equals the energy arriving in the kinetic store. Set the two equal and you can find a missing speed or height.

Worked example — speed of a falling ball

A 0.5 kg ball is dropped from a height of 1.8 m. Find its speed as it lands (ignore air resistance, g = 9.8 N/kg).

Ideag.p.e. lost = kinetic energy gained → mgh = ½mv²
g.p.e.Eₙ = 0.5 × 9.8 × 1.8 = 8.82 J
Rearrangev = √(2 × Eₖ ÷ m) = √(2 × 8.82 ÷ 0.5)
Answerv = √35.28 = 5.9 m/s
Quick check

A 2 kg bag is lifted 3 m onto a shelf. How much energy is transferred to its gravitational store? (g = 9.8 N/kg)

  • A6 J
  • B58.8 J
  • C29.4 J
  • D5.88 J
Show answer
B — 58.8 J. Eₙ = m g h = 2 × 9.8 × 3 = 58.8 J. (Answer C is the mistake of using g = 4.9; D is a decimal-point slip.)
Topic 2 — quick quiz
Click to reveal · 4 questions
  1. Write the kinetic energy equation and state the unit of each quantity.
    Ek = ½ m v². Kinetic energy in joules (J), mass in kg, speed in m/s.
  2. A 0.2 kg apple falls 2 m. Calculate the energy transferred from its gravitational store. (g = 9.8 N/kg)
    Ep = m g h = 0.2 × 9.8 × 2 = 3.92 J.
  3. A cyclist doubles their speed. What happens to their kinetic energy?
    It becomes four times bigger (KE ∝ v²). This is a favourite exam point.
  4. A 70 kg skydiver is moving at 50 m/s. Calculate the kinetic energy.
    Ek = ½ × 70 × 50² = ½ × 70 × 2500 = 87 500 J (87.5 kJ).
Topic 03 · 4.1.1.2 · Elastic energy

Elastic potential energy

The energy stored in a stretched or squashed spring — one given equation, and the small print that catches people out.

Part 1Storing energy in a spring

Stretch or compress a spring and you transfer energy (mechanically, by the force) into its elastic potential store. Let go and that energy is transferred back out.

Equation

Ee = ½ k e² given
elastic potential energy (J) = ½ × spring constant (N/m) × extension² (m)². Valid only while the limit of proportionality has not been exceeded.
natural length stretched extension e
Extension e is measured from the natural (unstretched) length

Worked example

A spring of spring constant 200 N/m is stretched by 0.10 m. Calculate the elastic potential energy stored.

EquationEₑ = ½ k e²
Sub in= ½ × 200 × 0.10² = ½ × 200 × 0.01
Answer= 1.0 J

⚠ Watch out — square the extension

It's the extension that's squared (e²), not the spring constant. Extension must be in metres (a 10 cm stretch is 0.10 m). This equation is on the sheet, so you don't have to memorise it — but you do have to use it correctly.

Quick check

A spring (k = 50 N/m) is stretched by 0.20 m. The elastic potential energy stored is:

  • A5 J
  • B1 J
  • C10 J
  • D2 J
Show answer
B — 1 J. Ee = ½ × 50 × 0.20² = ½ × 50 × 0.04 = 1 J. Answer A forgets to square the extension (½ × 50 × 0.2 = 5).
Topic 3 — quick quiz
Click to reveal · 3 questions
  1. What is the elastic potential energy equation, and which quantity is squared?
    Ee = ½ k e². The extension e is squared.
  2. A spring (k = 30 N/m) is compressed by 0.40 m. Calculate the elastic potential energy.
    Ee = ½ × 30 × 0.40² = ½ × 30 × 0.16 = 2.4 J.
  3. Why does the equation only work below the limit of proportionality?
    Beyond that limit the spring no longer extends in proportion to the force (it deforms permanently), so the simple ½ k e² relationship breaks down.
Topic 04 · 4.1.1.3 · Specific heat capacity

Specific heat capacity

Why water takes so long to heat up — one given equation, and the required practical that measures it.

Part 1What it means

The specific heat capacity of a material is the energy needed to raise the temperature of 1 kg of it by 1 °C. Water's is high (4200 J/kg °C), which is why it takes a lot of energy to heat — and why it's good for storing energy in heating systems.

Equation

ΔE = m c Δθ given
change in thermal energy (J) = mass (kg) × specific heat capacity (J/kg °C) × temperature change (°C)

Worked example — heating water

How much energy is needed to heat 2 kg of water from 20 °C to 50 °C? (c = 4200 J/kg °C)

Δθtemperature change = 50 − 20 = 30 °C
Sub inΔE = m c Δθ = 2 × 4200 × 30
Answer= 252 000 J (252 kJ)

⚠ Watch out — Δθ is the change

Δθ means the change in temperature, not the final temperature. Subtract start from finish first. The unit J/kg °C tells you the equation: joules per (kg × °C), so multiply by both.

Part 2Measuring it

Specific heat capacity of a metal block

Aim: determine the specific heat capacity of a material.

  1. Measure the mass of the metal block with a balance.
  2. Put an immersion heater in one hole and a thermometer in the other (add a drop of oil to the thermometer hole for good thermal contact). Record the starting temperature.
  3. Connect the heater through a joulemeter (or use power × time) to measure the energy supplied. Switch on for a set time.
  4. Record the highest temperature reached, then find Δθ.
  5. Calculate: c = ΔE ÷ (m × Δθ)

Control / improve: wrap the block in insulation to reduce energy lost to the surroundings. Because some energy still escapes, the measured value is usually a little higher than the true value.

metal block mass m immersion heater thermometer
Apparatus (insulation dashed) — energy in measured by a joulemeter, or power × time
Quick check

It takes 9000 J to raise 0.5 kg of a metal by 40 °C. What is its specific heat capacity?

  • A180 J/kg °C
  • B450 J/kg °C
  • C720 J/kg °C
  • D4500 J/kg °C
Show answer
B — 450 J/kg °C. c = ΔE ÷ (m × Δθ) = 9000 ÷ (0.5 × 40) = 9000 ÷ 20 = 450 J/kg °C.
Topic 4 — quick quiz
Click to reveal · 4 questions
  1. Define specific heat capacity.
    The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
  2. Calculate the energy to heat 0.5 kg of aluminium (c = 900 J/kg °C) by 20 °C.
    ΔE = m c Δθ = 0.5 × 900 × 20 = 9000 J.
  3. In the required practical, why is the measured value usually too high?
    Some energy from the heater is transferred to the surroundings instead of the block, so the apparatus seems to need more energy per degree than it really does. Insulation reduces this.
  4. Why does water make a good coolant and storage heater?
    Its high specific heat capacity means it can absorb/store a lot of energy with only a small temperature change.
Topic 05 · 4.1.1.4 · Power

Power — the rate of transfer

Two equations, one unit, and the difference between being powerful and transferring a lot of energy.

Part 1Energy per second

Power is the rate of energy transfer — the energy transferred (or work done) every second. It's measured in watts (W), where 1 watt = 1 joule per second.

Equations

P = E / t recall
power (W) = energy transferred (J) ÷ time (s)
P = W / t recall
power (W) = work done (J) ÷ time (s) — same idea, since work done is energy transferred

Worked example — power of a motor

A motor transfers 4800 J of energy in 8 s. Calculate its power.

EquationP = E ÷ t
Sub in= 4800 ÷ 8
Answer= 600 W

⚠ Watch out — power isn't energy

A 60 W lamp left on for an hour transfers more total energy than a 2000 W kettle on for 30 s — but the kettle is far more powerful. Power = rate; energy = total. Two machines that do the same job, the more powerful one does it in less time.

SAME JOB, DIFFERENT TIME Crane A lifts in 4 s higher power Crane B lifts in 12 s lower power Both transfer the same energy — A just does it faster.
More power = same energy transferred in less time
Quick check

A light bulb transfers 1800 J in 30 s. What is its power?

  • A54 000 W
  • B60 W
  • C600 W
  • D6 W
Show answer
B — 60 W. P = E ÷ t = 1800 ÷ 30 = 60 W. Answer A is the slip of multiplying instead of dividing.
Topic 5 — quick quiz
Click to reveal · 4 questions
  1. Define power and state its unit.
    Power is the rate of energy transfer (energy transferred per second). Unit: the watt (W) = 1 J/s.
  2. A kettle transfers 360 000 J in 120 s. Calculate its power.
    P = E ÷ t = 360 000 ÷ 120 = 3000 W (3 kW).
  3. Motor A and motor B both raise the same load to the same shelf, but A is quicker. Which has the greater power?
    Motor A. Same energy transferred in less time means greater power.
  4. A crane does 90 000 J of work in 30 s. Find its power output.
    P = W ÷ t = 90 000 ÷ 30 = 3000 W.
Topic 06 · 4.1.2.1 · Transfers & dissipation

Conservation & wasted energy

Energy is always conserved — but a lot of it ends up spread out and useless. How we cut that down.

Part 1Conservation & dissipation

The principle of conservation of energy: energy cannot be created or destroyed, only transferred, stored or dissipated. In a closed system, the total energy never changes.

But in any real transfer, some energy is dissipated — transferred to the surroundings, usually by heating, where it spreads out and becomes useless. We loosely call this "wasted" energy. It isn't destroyed; it's just no longer useful.

device input energy useful transfer dissipated to surroundings (by heating)
Useful output + dissipated energy = total input (energy is conserved)

⚠ Watch out — "wasted" doesn't mean "destroyed"

Wasted energy is still there — it's been dissipated to the surroundings and spread thinly, so we can't usefully get it back. Saying it was "lost" or "destroyed" loses marks. Total energy is always conserved.

Part 2Reducing unwanted transfers

Two big ways to cut wasted energy:

Lubrication — oil or grease between moving parts reduces friction, so less energy is dissipated by heating.

Insulation — materials with low thermal conductivity slow the transfer of energy by heating, keeping warmth in (or out).

Thermal conductivity is how quickly a material conducts energy. A building cools more slowly if its walls are thick and have a low thermal conductivity.

Keywords

Dissipated
Transferred to the surroundings and spread out, so it's no longer useful.
Lubrication
Reducing friction between surfaces (e.g. with oil) to cut energy wasted by heating.
Thermal conductivity
How readily a material transfers energy by conduction — low means a good insulator.
Quick check

Two houses are identical except house X has thicker walls of lower thermal conductivity. Which cools down faster on a cold night?

  • AHouse X — thicker walls trap more cold
  • BThe other house — its walls conduct energy out faster
  • CThey cool at the same rate
  • DYou can't tell without the temperatures
Show answer
B. House X has thicker walls and lower thermal conductivity, so it loses energy by heating more slowly. The other house conducts energy out faster, so it cools faster.
Topic 6 — quick quiz
Click to reveal · 4 questions
  1. State the principle of conservation of energy.
    Energy cannot be created or destroyed, only transferred, stored or dissipated. (In a closed system the total stays constant.)
  2. What does "dissipated" mean?
    Energy transferred to the surroundings (usually by heating) and spread out, so it's no longer useful.
  3. Give two ways to reduce unwanted energy transfers in a machine.
    Lubrication (reduces friction) and insulation / using low-thermal-conductivity materials (reduces transfer by heating).
  4. Name two wall properties that slow the cooling of a building.
    Greater wall thickness and lower thermal conductivity.
Topic 07 · 4.1.2.2 · Efficiency

Efficiency

What fraction of the energy went where you wanted it — and the Higher-tier version using power.

Part 1The efficiency equation

Efficiency is the fraction of the input energy that is transferred usefully. The rest is dissipated.

Equation

efficiency = useful output energy transfer ÷ total input energy transfer recall
Answer is a decimal between 0 and 1 — multiply by 100 for a percentage.

Worked example

A motor is supplied with 200 J. Of this, 50 J is usefully transferred to the kinetic store. Calculate the efficiency.

Equationefficiency = useful ÷ total
Sub in= 50 ÷ 200 = 0.25
Answer= 0.25, or 25%
SANKEY: WHERE THE ENERGY GOES input 200 J useful 50 J (25%) wasted 150 J (75%)
A Sankey diagram: arrow width shows the amount of energy

⚠ Watch out — efficiency can't beat 100%

Efficiency is always less than 1 (100%) because some energy is always dissipated. If you calculate more than 1, you've divided the wrong way round — useful goes on top.

Higher tier — efficiency from power

On Higher tier you can also use the power form:

efficiency = useful power output ÷ total power input

Example: a pump draws 500 W and usefully outputs 350 W. Efficiency = 350 ÷ 500 = 0.70 = 70%.

Part 2Improving efficiency

To make a device more efficient, reduce the energy it wastes: lubricate moving parts to cut friction, insulate to cut energy transferred by heating, and reduce air resistance or use lower-resistance wires. Every one of these moves more of the input into the useful output.

Quick check

A lamp is supplied with 80 J and usefully transfers 8 J as light. What is its efficiency?

  • A0.1 (10%)
  • B10 (1000%)
  • C0.9 (90%)
  • D0.8 (80%)
Show answer
A — 0.1, or 10%. efficiency = useful ÷ total = 8 ÷ 80 = 0.1. (Filament lamps really are this wasteful — most energy is dissipated by heating.)
Topic 7 — quick quiz
Click to reveal · 4 questions
  1. Write the (Foundation) efficiency equation.
    efficiency = useful output energy transfer ÷ total input energy transfer (× 100 for %).
  2. A device wastes 120 J out of 150 J input. Calculate its efficiency.
    Useful = 150 − 120 = 30 J. Efficiency = 30 ÷ 150 = 0.2 = 20%.
  3. [HT] A machine has a useful power output of 240 W from a total input power of 800 W. Find the efficiency.
    efficiency = 240 ÷ 800 = 0.30 = 30%.
  4. Give one way to make an electric drill more efficient.
    Any sensible reduction of waste, e.g. lubricate the moving parts to reduce friction (so less energy is dissipated by heating).
Topic 08 · 4.1.3 · Energy resources

Energy resources

Renewable vs non-renewable, what we use them for, and how to write a balanced evaluation — the no-maths topic that needs the most thinking.

Part 1Renewable vs non-renewable

A non-renewable resource is finite — once used, it's gone on a human timescale. A renewable resource is replenished as fast as (or faster than) it's used.

NON-RENEWABLE Coal Oil Natural gas Nuclear fuel RENEWABLE Solar · Wind · Hydro Tidal · Waves Geothermal Bio-fuel
The resources you need to know, sorted by type

The three main uses are transport, generating electricity, and heating. Most transport still relies on oil (petrol/diesel); electricity comes from a changing mix; heating uses gas, electricity and increasingly heat pumps.

⚠ Watch out — common traps

Nuclear is non-renewable (uranium is finite) but it's low-carbon — don't confuse "renewable" with "clean". Bio-fuels are renewable and roughly carbon-neutral, but growing them uses land. "Renewable" does not mean "no environmental impact".

Part 2Reliability, impact & trends

Reliability: fossil fuels and nuclear can supply power on demand; tidal and geothermal are predictable; but wind and solar are intermittent — they only work when it's windy or sunny.

Environmental impact: burning fossil fuels releases carbon dioxide (a greenhouse gas, driving climate change) and other pollutants; nuclear produces dangerous radioactive waste and carries a small risk of major accidents; wind farms, hydroelectric dams and tidal barrages affect habitats and landscapes.

Trends: use of renewables is increasing as concern grows about climate change and as fossil fuels run low. But switching is slowed by cost, reliability and the scale of existing infrastructure. Science can describe the options and consequences; the final decisions also involve economic, political, social and ethical factors.

How to answer an "evaluate" question

"Evaluate the use of wind power for generating electricity." (How to structure it.)

ForRenewable, no CO₂ when running, low running costs.
AgainstIntermittent (no wind = no power), visual/noise impact, high set-up cost.
ConclusionGive a justified judgement — e.g. good as part of a mix, but needs backup for calm days.
Quick check

Which resource is non-renewable but does not release carbon dioxide when generating electricity?

  • ANatural gas
  • BNuclear
  • CWind
  • DCoal
Show answer
B — Nuclear. Uranium is finite (so non-renewable), but the reactor releases no CO₂ in use. Its drawback is radioactive waste. Wind is low-carbon too, but it is renewable.
Topic 8 — quick quiz
Click to reveal · 4 questions
  1. Give two non-renewable and two renewable energy resources.
    Non-renewable: any two of coal, oil, natural gas, nuclear fuel. Renewable: any two of solar, wind, hydroelectric, tidal, waves, geothermal, bio-fuel.
  2. Why are wind and solar described as unreliable?
    They are intermittent — they only generate when it's windy or sunny, so supply doesn't always match demand.
  3. State one environmental drawback of (a) fossil fuels and (b) nuclear power.
    (a) Burning releases CO₂ and pollutants (climate change). (b) Produces radioactive waste and a risk of accidents.
  4. Why are decisions about energy resources not purely scientific?
    They also involve economic, political, social and ethical factors — science sets out the options and consequences, but people weigh up the trade-offs.
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