Year 7 · Science · Energy · Lesson 3
Energy in food and paying for electricity
Energy in food (kilojoules), how activities use energy, energy balance, and calculating the cost of electricity using kilowatt-hours.
18-minute video lesson
Teaching, worked examples and 20 practice questions solved step by step.
Watch free for a monthWhat your child will learn
- Compare energy in foods
- Explain energy balance
- Calculate energy in kWh
- Calculate the cost of electricity
The method
- kW + hours.
- kWh.
- x price.
- Pence / pounds.
Key words: kilojoule, energy balance, power, kilowatt-hour, cost, kilowatt.
Worked examples
The first three practice questions from the lesson, with every step.
Question 1
What unit is food energy measured in?
- Step 1: kJ
Answer: kilojoules
Question 2
How many joules in 1 kJ?
- Step 1: Kilo
Answer: 1000
Question 3
Which has more energy per 100 g: apple or chocolate?
- Step 1: Table
Answer: chocolate (2200 kJ)