O-Level and SEC G3 Physics K323
P6: Energy
Track energy stores and transfers, calculate work, power, and efficiency, and state the system boundary.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Energy questions require a defined system, named stores and transfer pathways, conservation, and consistent units. Evaluation questions compare energy resources using efficiency, cost, reliability and environmental impact.
Stores, transfers and conservation
Energy can be stored kinetically, gravitationally, chemically, elastically, internally or nuclearly. It transfers mechanically, electrically, by heating, or by waves. Name both the initial and final stores and the pathway when explaining a change.
Conservation means total energy remains constant in a closed system. Energy described as wasted is transferred to less useful stores, often internal energy of the surroundings. It has not disappeared.
Work, power and efficiency
Work done is energy transferred mechanically when a force moves an object through a distance in the force direction. Power measures how quickly energy is transferred, so two devices can transfer the same energy with different powers.
Efficiency compares useful output with total input and cannot exceed one, or . Match energy output with energy input, or power output with power input. Do not mix energy and power in one ratio.
Electricity-generation resources
Non-renewable resources include fossil fuels and nuclear fuel. Renewable examples include biofuel, wind, tides, hydropower, geothermal and solar. No resource is simply good or bad in every setting.
A strong evaluation compares the same criteria: conversion efficiency, capital and operating cost, reliability or intermittency, location limits, emissions, waste, habitat effects and timescale. A justified conclusion depends on the stated context.
Formulae and relationships
| Relationship | Use |
|---|---|
| Find kinetic energy. | |
| Find near-Earth gravitational potential energy. | |
| Find work when distance is along the force. | |
| Find power. | |
| Find efficiency. |
Worked examples
Example 1: A motor takes electrically and raises a load whose gravitational potential energy increases by in . Find efficiency and useful power.
- Efficiency: , or .
- Useful power: .
- The remaining energy is transferred to less useful stores such as heating and sound.
Answer: Efficiency ; useful power .
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Define the system before tracking energy stores and transfer pathways.
- Distinguish work, energy, power, and efficiency through their units and time dependence.
- Evaluate energy resources using evidence about reliability, impact, cost, and renewability.
Official outcome coverage
K323 P6: 7 mapped outcomes, references P6(a), P6(b), P6(c), P6(d), P6(e), P6(f), P6(g). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Measure an energy input and useful output, state major losses, and calculate efficiency without mixing joules, watts, and kilowatt-hours.
Exam traps and retrieval check
Avoid these traps
- Saying energy is used up rather than transferred.
- Using speed instead of squared speed in kinetic energy.
- Giving an energy-resource conclusion without comparing the requested criteria.
Check from memory
Can efficiency exceed ?
No, because useful output cannot exceed total input in a valid boundary.
What is the difference between energy and power?
Energy is the quantity transferred; power is its transfer rate.
Why is wind power not fully reliable alone?
Its output depends on variable wind conditions and may need storage or backup.
Pure versus Combined scope
Combined Physics revisits part of this core under CP6 Energy, but with reduced outcome scope. Combined students should follow the component checklist rather than assume every K323 outcome is assessable.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.