Understanding Physics: Energy resources and energy transfers: Edexcel IGCSE Science Single Award Explained

Energy is the unifying concept across all three sciences in the single award, and this section formalises what the biology and chemistry sections have been using all along

The energy resources and energy transfers section of the Pearson Edexcel IGCSE Science Single Award (4SS0) sits at the heart of the physics content. Energy stores, energy transfers, efficiency, work and power are concepts that appear throughout the specification, from photosynthesis in biology to exothermic reactions in chemistry. This section gives them their formal treatment, complete with the equations and calculation techniques you will need for the exam.

These edexcel igcse science single award revision notes cover the three topics within the section: units, energy transfers, and work and power. The approach is precise and scholarly, as befits a section where every specification point has a corresponding equation or defined term. Use these as your edexcel igcse science single award notes for systematic revision, and verify your understanding with the self-check questions at the end.

Units

Quantity	Unit	Symbol
Mass	kilogram	kg
Energy / work done	joule	J
Distance / height	metre	m
Speed	metre per second	m/s
Acceleration	metre per second squared	m/s²
Force	newton	N
Time	second	s
Power	watt	W

A watt is one joule per second (1 W = 1 J/s). This definition is worth remembering because it links the concepts of energy, power and time in a single statement.

Energy transfers

Energy stores and transfer pathways

The specification uses the language of energy stores and energy transfer pathways. An energy store is a way of accounting for energy in a system. The eight energy stores named in the specification are:

Chemical: energy stored in the bonds of chemical compounds (fuels, food, batteries).
Kinetic: energy of a moving object.
Gravitational potential: energy stored by an object raised above the ground.
Elastic potential: energy stored in a stretched or compressed object (springs, elastic bands).
Thermal: energy related to the temperature of an object (the total kinetic energy of its particles).
Magnetic: energy stored in magnetic fields.
Electrostatic: energy stored in electric fields.
Nuclear: energy stored in the nuclei of atoms.

Energy is transferred between stores by four pathways:

Mechanically: by a force acting on an object (pushing, pulling, stretching).
Electrically: by charges flowing through a circuit.
By heating: energy moves from a hotter region to a cooler one.
By radiation: energy carried by electromagnetic waves (light, infrared, etc.).

Conservation of energy

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another. The total energy in a closed system remains constant. When a ball is thrown upward, kinetic energy is transferred to gravitational potential energy. When it falls back down, the transfer reverses. In practice, some energy is always transferred to thermal stores (through friction or air resistance), which is why no real process is perfectly efficient.

Efficiency

Efficiency measures how much of the input energy is usefully transferred. The equation is:

efficiency = useful energy output / total energy input

Efficiency is often expressed as a percentage by multiplying the result by 100. No device is 100% efficient because some energy is always dissipated (spread out) as thermal energy.

Worked example: A motor receives 500 J of electrical energy and converts 350 J into useful kinetic energy. The rest is dissipated as heat. What is the efficiency?

Efficiency = 350 / 500 = 0.70 = 70%.

Sankey diagrams

A Sankey diagram is a visual representation of energy transfer. The width of each arrow is proportional to the amount of energy it represents. The input arrow enters from the left, the useful output arrow continues to the right, and the wasted energy arrows branch off (usually downward). The total width of the output arrows must equal the width of the input arrow, reflecting conservation of energy.

The specification requires you to describe a variety of everyday devices using Sankey diagrams. For example, a filament lamp might receive 100 J of electrical energy and convert 10 J into light (useful) and 90 J into heat (wasted), giving an efficiency of 10%.

Work and power

Work done

Work is done when a force moves an object through a distance in the direction of the force. The equation is:

W = F x d

where W is work done in joules, F is force in newtons, and d is distance in metres.

Work done is equal to energy transferred. If you push a box with a force of 50 N over a distance of 3 m, you do 50 x 3 = 150 J of work, and 150 J of energy is transferred from your chemical store to the kinetic store of the box (and the thermal store of the surfaces, through friction).

Worked example: A crane lifts a 200 kg steel beam through a height of 15 m. Calculate the work done against gravity. (g = 10 N/kg.)

First, calculate the weight: W = m x g = 200 x 10 = 2000 N.
Then, calculate the work done: W = F x d = 2000 x 15 = 30,000 J (30 kJ).

Gravitational potential energy

The energy stored by an object because of its height above the ground is given by:

GPE = m x g x h

where GPE is gravitational potential energy in joules, m is mass in kg, g is gravitational field strength in N/kg, and h is height in metres.

Kinetic energy

The energy of a moving object is given by:

KE = 0.5 x m x v²

where KE is kinetic energy in joules, m is mass in kg, and v is speed in m/s.

Notice that kinetic energy depends on the square of the speed. Doubling the speed quadruples the kinetic energy. This has direct implications for stopping distances (covered in the forces section) and for the severity of collisions.

Worked example: A 0.5 kg ball is thrown at 12 m/s. What is its kinetic energy?

KE = 0.5 x m x v² = 0.5 x 0.5 x 12² = 0.5 x 0.5 x 144 = 36 J.

Conservation of energy in practice

The specification requires you to understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work. When a ball falls freely from rest, its gravitational potential energy is converted into kinetic energy. At any point during the fall (ignoring air resistance):

GPE lost = KE gained

This means: m x g x h = 0.5 x m x v²

The mass cancels, giving: g x h = 0.5 x v², which you can rearrange to find the speed at any height, or the height from which an object must fall to reach a given speed.

Power

Power is the rate of transfer of energy, or equivalently, the rate of doing work:

P = W / t

where P is power in watts, W is work done (or energy transferred) in joules, and t is time in seconds.

Worked example: A student climbs a flight of stairs, doing 3000 J of work against gravity in 12 s. What is their power output?

P = W / t = 3000 / 12 = 250 W.

Common mistakes in energy calculations

Forgetting to square the speed in KE = 0.5mv². The v² term is critical. If you forget it, you will get an answer that is far too small and does not match the units.
Confusing work and power. Work is the total energy transferred (in joules). Power is the rate of transfer (in watts, which are joules per second). A student who climbs stairs slowly does the same amount of work as one who runs, but the runner has a higher power output.
Using the wrong value of g. Unless the question states otherwise, use g = 10 N/kg for calculations on Earth.
Expressing efficiency as a fraction when the question asks for a percentage, or vice versa. Read the question carefully.

Self-check questions

Name the eight energy stores listed in the specification.
State the principle of conservation of energy.
A kettle receives 200,000 J of electrical energy and transfers 180,000 J to heat the water. Calculate its efficiency as a percentage.
A force of 80 N pushes a trolley 6 m along a flat surface. Calculate the work done.
Calculate the gravitational potential energy of a 3 kg book on a shelf 2.5 m above the floor. (g = 10 N/kg.)
A 60 kg runner sprints at 8 m/s. Calculate their kinetic energy.
A ball is dropped from a height of 20 m. Using conservation of energy (and ignoring air resistance), calculate the speed at which it hits the ground. (g = 10 N/kg.)
A motor does 12,000 J of work in 30 s. Calculate its power output.

Energy in the context of the single award

The physics: energy resources and energy transfers edexcel igcse section is the most equation-dense part of the physics content. Five equations (efficiency, W = Fd, GPE = mgh, KE = 0.5mv², P = W/t) provide the backbone of the entire section. The conceptual framework (stores, pathways, conservation, Sankey diagrams) gives those equations meaning. Together, they account for a substantial share of the marks on the physics paper.

For your igcse 4ss0 physics: energy resources and energy transfers revision, write out each equation, practise rearranging it to solve for every variable, and work through at least three numerical examples of each. The exam will test these in contexts you have not seen before, so your fluency with the equations matters more than memorising specific examples.

These edexcel igcse science single award notes provide the framework. Test yourself with edexcel igcse science single award practice questions from past papers to develop the speed and accuracy you need. The edexcel igcse science single award explained approach here gives you the conceptual grounding; the exam rewards precise calculation. The Green Bridge CBT platform offers energy questions organised by equation and topic, allowing you to drill each calculation type until it becomes second nature.