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Unit summary

Check your knowledge and understanding

1. Copy the table below. Then complete it for
the lamps, using the information provided in
the picture. electric motors diesel engines
textbooks nis edu kz
90% efficient about 35–40% efficient
Type of Energy Energy Efficiency
lamp transferred transferred (%)
as light (%) as heat (%) steam engines

petrol engines
25% efficient 7% or even less efficient

a) Which engine is the most efficient? Explain
your answer.
2. Write down the
filament
three types of lamp lamp b) What two sorts of ‘waste’ energy do all the
in order, starting with 4% light engines produce?
96% heat
the most efficient c) Railways changed from steam engines to
and ending with the diesel engines and then to electric trains.
least efficient. Why did this happen? Explain your answer.

3. You use an engine fluorescent tube d) Imagine that you used 100 litres of petrol on
25% light 75% heat
to do some sort of a long car journey. How many litres would be
job for you, so you doing useful work? What would happen to
want it to use most the rest?
of its energy for that
sodium vapour 4. A skier is skiing down the hill. Describe how
purpose. The less street lamp
energy the engine 40% light transfer of energy occurs in this case.
60% heat
‘wastes’, the more 5. When does a vehicle consume more fuel – in
efficient it is. uniform motion or in motion with stops? Explain
your answer in terms of change of kinetic energy.

Assess your learning

Reflect on how well you met the learning objectives of this unit. Use the worksheet provided by
your teachers to develop your own targets.

How confident am I?

I can …
give examples of energy in different forms, its conversion and conservation

apply the principle of energy conservation to simple examples
determine the concept of efficiency and solve problems

distinguish between two types of mechanical energy (kinetic and potential)
recall and apply the formula E k = mv /2
2

recall and apply the formula E p = mgh for potential energy changes near the Earth’s surface

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