S4.9.8 For the adult
Energy at home
A 1 kW iron is used for 2 hours. How much energy does it use?
What this chapter teaches
Homes pay for energy in kilowatt hours, found as power in kW times time in hours. The cost is the energy times the price for each kWh. An LED lamp gives the same light as a filament lamp with much less power, so it costs much less to run.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you work out the energy a 2 kW heater uses in 3 hours?
- Why can a television cost more to run in a day than a kettle?
- How would you compare the yearly cost of two lamps?
After the chapter, the learner can
- Calculate the cost of running an appliance from its power and time
- Compare the yearly cost of a filament lamp and an LED lamp
What they copy into their notebook
E (kWh) = P (kW) × t (h). W to kW: ÷ 1 000. Minutes to hours: ÷ 60. Cost = kWh × price. 1 kWh = 3.6 MJ. LED lamp: same light, less power, lower cost.