This module joins three things: how much electrical energy a device transfers, how household safety parts (fuse, switch, earth wire) behave, and how to explain what has gone wrong when a circuit does not work. The calculations are short. The marks are usually lost on units and on explanations that stop one step early.
Check the current Cambridge IGCSE Physics 0625 syllabus for your exam year to see exactly which statements are listed under this topic.
What should you know before starting?
You should know current, potential difference and resistance from charge and current and potential difference, resistance and circuits. You also need the idea of power and energy from work, energy and efficiency and power and energy resources. Basic rearranging of an equation is enough.
An orienting example
An invented hairdryer setting is rated 230 V and 460 W. What current does it take, and how much energy does it transfer in 10 minutes?
Current: I = P ÷ V = 460 ÷ 230 = 2.0 A.
Time: 10 minutes = 600 s. Energy: E = P × t = 460 × 600 = 276 000 J, which is 276 kJ.
Check with the other route: E = I × V × t = 2.0 × 230 × 600 = 276 000 J. Both routes agree, so the working is consistent.
In what order should you study the lessons?
- Calculate electrical energy from stated ratings: start with P = IV and E = Pt using the numbers printed on a device.
- Compare a fuse purpose with a switch purpose: two parts that both “stop the current”, for very different reasons.
- Interpret earthing on a supplied diagram: read what the earth wire does when a fault happens.
- Explain a circuit fault without giving mains-work instructions: explain open and short circuits using safe low-voltage examples.
- Check a unit conversion in an energy-use calculation: watts to kilowatts, minutes to hours, joules to kWh.
What traps catch students in this topic?
- Mixed units. Watts with hours, or kilowatts with seconds, gives a wrong answer that still looks like a sensible number.
- Confusing the roles of fuse and switch. A fuse is a protection part that melts on too large a current. A switch is a control chosen by the user.
- Choosing the largest fuse “to be safe”. A fuse rated far above the normal current will not protect the wiring.
- Stopping the explanation early. “The fuse blows” is incomplete. Say why the current became large and what the break achieves.
- Treating practical safety as a recipe. This course asks you to interpret diagrams and explain, not to carry out mains work.
How should you use the practice set?
Work through the lessons first, then try the electrical energy practice set on paper. Open each answer only after a full attempt, and use the table at the end to route each slip back to a lesson. The mistake log and retest queue helps you record which kind of slip repeated.
For more of the subject, see the Physics learning guide. Students who follow each formula but still drop marks on units and explanations often benefit from online one-to-one Physics tuition, where a teacher reads your working line by line.