This cluster trains the numeric side of electricity and energy: reading a power and time table, following an energy-flow diagram, checking an efficiency claim and comparing two systems fairly. It sits inside force and motion, because both topics reward the same habit of writing units with every number.
The lessons use invented classroom devices so that you can see the assumptions. The method carries over to any real appliance you meet in a question.
How do the parts connect?
Everything starts with energy = power × time. That formula turns a table of watts and hours into a total, which is the first skill.
An energy-flow diagram splits the input into useful and wasted parts, so it needs the same unit discipline. Efficiency then asks what fraction of the input is useful, which explains why it cannot pass 100%. The last lesson asks you to compare two systems, which is only fair if their assumptions match.
A small orienting example
An invented classroom fan is rated at 60 W and runs for 5 hours. Energy = 60 W × 5 h = 300 Wh, which is 0.3 kWh.
Suppose the question says the school pays RM0.40 for each kWh, as an assumption. The cost is 0.3 × 0.40 = RM0.12.
Three things in that example repeat throughout the cluster: a formula, a unit conversion from Wh to kWh and a stated assumption about the rate.
Who should start where?
- Unsure how to use a table of watts and hours: start with calculating energy from a device table.
- Mixing units on diagrams: read interpreting an energy-flow diagram with consistent units.
- Confused by efficiency above 100%: go to why efficiency cannot exceed the stated input.
- Ready for mixed questions: use the integrated practice set.
For a teacher who works through your own energy tables with you, see online one-to-one Science tuition.