Energy transfers and efficiency
Energy transfers, efficiency and wasted energy, and comparing energy sources. Read one part at a time and tap “I know this”. Then test yourself in the quiz.
Know it already? Jump straight to the quiz
Energy transfers
| Example | Transfer |
|---|---|
| Bicycle dynamo for a light | Kinetic → electrical |
| Phone battery charging | Electrical → chemical |
| Firework explodes | Chemical → sound, light, heat, movement |
| Spring released | Elastic potential → kinetic |
| Solar panel charging batteries in the day | Light → electrical → chemical (stored in the battery for the night) |
The cyclist’s energy first comes from the food she ate (chemical).
The toy car’s track
A toy car with no motor rolls down from a high point. At the top it has the most gravitational potential energy; in the dip the most kinetic energy. Gravity pulls it down. It can never climb higher than its starting point, because it cannot gain extra energy. Friction turns some energy into heat, so it does not even get back up to its starting height.
Comparing energy sources
| Source | Limitation |
|---|---|
| Solar | No sunlight at night |
| Wind | The wind does not always blow |
| Fossil fuels | Non-renewable: millions of years to form |
| Nuclear (uranium) | Dangerous waste |
A candle under a glass jar goes out: the oxygen inside gets used up.
Remember this and test yourself
- Efficient: the device turns most of its energy into useful energy.
- Wasted energy = total − useful: a kettle uses 2 000 J and 1 600 J heats the water, so 400 J is wasted.
- A bouncing ball loses energy as heat and sound; a car engine gets hot, because most fuel energy becomes heat.
- Dynamo: kinetic → electrical. Phone charging: electrical → chemical. Phone playing music: chemical → electrical → sound.
- Nuclear power uses uranium; geothermal energy is heat from inside the Earth; hydrogen burns to make mainly water.
Write these points in your book. Read them again the night before the test.
Efficient = little heat waste. Ask: how much of the energy did the job I wanted?
Important words
First say what the word means, then turn the card over.
Match column A to column B
Tap a word in column A, then its meaning in column B. You can also start in column B.
True or false?
Read the question and the answer. Is the answer right? Tap True or False.
Now the real quiz!
The quiz has many more questions on this topic. Every question shows straight away whether you are right and explains why.
Take the quiz: Energy transfers and efficiency- Read one part together and ask your child to tell it back in their own words.
- The ticks (“I know this”) are saved on this device only. We never ask for names or emails.
Follows CAPS for Grade 7 Natural Sciences. Always check your teacher’s notes and textbook too.