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Science Quiz - Physics - Wasted Energy and Efficiency (AQA) (Questions)

Explore wasted energy and efficiency in GCSE Physics, learning how machines lose energy, how to reduce losses, and how to calculate efficiency using simple examples and equations.

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Fascinating Fact:

Friction and air resistance turn kinetic energy into thermal energy. Lubrication and streamlining help reduce this.

In GCSE Science (Physics), you study how energy is stored, transferred and sometimes wasted. You use efficiency to compare devices and explain how design changes can improve useful energy output.

Key Terms

Efficiency: A measure of how much of the input energy is transferred usefully, often written as a decimal or percentage.
Useful energy: Energy transferred to the store you want, such as kinetic energy in moving parts or light from a lamp.
Wasted energy: Energy transferred to less useful stores, often spreading out as thermal energy to the surroundings.

Frequently Asked Questions (Click to see answers)

What is wasted energy in GCSE physics?

In GCSE Physics, wasted energy is energy that is not transferred to a useful store. It often ends up as thermal energy in the surroundings, making the device less efficient.

How do you calculate efficiency in GCSE physics?

You calculate efficiency by dividing useful output energy by total input energy. You can leave it as a decimal or multiply by 100 to give a percentage.

How can wasted energy be reduced in everyday machines?

Wasted energy can be reduced by using lubrication to cut down friction, streamlining to reduce air resistance, and insulation to limit heat loss from hot objects or buildings.

Try These Related Quizzes

1.

As a train travels along its rails, its wheels create sparks. Apart from this light energy, what other forms of energy are wasted?

[ ]	Sound only
[ ]	Heat only
[ ]	Kinetic only
[ ]	Heat and sound

2.

What is a Sankey diagram?

[ ]	A diagram of the London Underground railway system
[ ]	A diagram drawn to scale (usually using squared paper) to represent the efficiency of an energy transfer
[ ]	A circuit diagram for a machine that can be used for measuring the efficiency of energy transfers
[ ]	A graph showing only the percentage of useful energy produced in an energy transfer

3.

How is the efficiency of an energy transfer expressed?

[ ]	As a percentage
[ ]	As a proportion
[ ]	As a ratio
[ ]	In kilowatt hours

4.

If a filament light bulb consumes 150 J/s and produces 12 J/s of light energy, what is its efficiency?

[ ]	0.08%
[ ]	8%
[ ]	12.5%
[ ]	1,250%

5.

A houseowner replaces their filament light bulbs with LED lighting. This is 85% efficient and requires only a 7 watt input. What is the useful power output of the new lights?

[ ]	2.95 W
[ ]	3.95W
[ ]	4.95 W
[ ]	5.95 W

6.

When the outside temperature is cold, the air inside a car is warmed by some of the thermal energy from the engine. What effect does this have on the overall efficiency of the car engine?

[ ]	It remains the same
[ ]	It increases
[ ]	It decreases
[ ]	A Sankey diagram is needed to work it out

7.

What is the efficiency of a computer that consumes 25 J/s of electrical energy and wastes 9 J/s of heat energy?

[ ]	278%
[ ]	36%
[ ]	0.36%
[ ]	64%

8.

Burning 2kg of wood in a particular woodburning stove releases 29 MJ of heat energy. If 25 MJ of that heat is transferred to the room, which of the following statements is true?

[ ]	The fire is 100% efficient
[ ]	The fire is between 90% and 100% efficient
[ ]	The fire is between 85% and 90% efficient
[ ]	The efficiency of the fire is less than 85%

9.

Distributing electrical energy through the 400,000 V cables of the National Grid wastes some of the energy of the electricity (see below). What is the efficiency of this part of the system to the nearest whole number?

Total power generated: 62,161.5 MW
Step-up transformer losses: 157 MW
Step-down transformer losses: 142 MW
Losses caused by heating of the cables during transmission: 1.4%

[ ]	99%
[ ]	98%
[ ]	97%
[ ]	96%

10.

A roof receives 1,000 W/m² of energy from the Sun on a clear, sunny day. How many watts would be produced from a 5cm wide by 20cm long solar cell positioned on the roof if the efficiency of the solar cell is 14%?

[ ]	1.4 W
[ ]	1.6 W
[ ]	14,000 W
[ ]	14 kW

You can find more about this topic by visiting BBC Bitesize - Changes in energy stores - AQA

Science Quiz - Physics - Wasted Energy and Efficiency (AQA) (Answers)

1.

As a train travels along its rails, its wheels create sparks. Apart from this light energy, what other forms of energy are wasted?

[ ]	Sound only
[ ]	Heat only
[ ]	Kinetic only
[x]	Heat and sound

The key useful energy transfer is to produce kinetic energy. The noise of the train and friction waste energy in the form of heat and sound

2.

What is a Sankey diagram?

[ ]	A diagram of the London Underground railway system
[x]	A diagram drawn to scale (usually using squared paper) to represent the efficiency of an energy transfer
[ ]	A circuit diagram for a machine that can be used for measuring the efficiency of energy transfers
[ ]	A graph showing only the percentage of useful energy produced in an energy transfer

These crop up almost every year in the exams

3.

How is the efficiency of an energy transfer expressed?

[x]	As a percentage
[ ]	As a proportion
[ ]	As a ratio
[ ]	In kilowatt hours

Efficiency is always a percentage worked out by dividing the output energy by the input energy and multipying by 100

4.

If a filament light bulb consumes 150 J/s and produces 12 J/s of light energy, what is its efficiency?

[ ]	0.08%
[x]	8%
[ ]	12.5%
[ ]	1,250%

Answer four would be what you got if you did the division the wrong way round. The majority of the electrical energy is wasted as heat

5.

A houseowner replaces their filament light bulbs with LED lighting. This is 85% efficient and requires only a 7 watt input. What is the useful power output of the new lights?

[ ]	2.95 W
[ ]	3.95W
[ ]	4.95 W
[x]	5.95 W

Not only does LED lighting consume a fraction of the power of a filament lamp, it is also much more efficient at transferring the electrical energy to useful light energy

6.

When the outside temperature is cold, the air inside a car is warmed by some of the thermal energy from the engine. What effect does this have on the overall efficiency of the car engine?

[ ]	It remains the same
[x]	It increases
[ ]	It decreases
[ ]	A Sankey diagram is needed to work it out

Since this is a useful energy transfer, it increases the overall efficiency by using some of the heat energy that would otherwise be wasted

7.

What is the efficiency of a computer that consumes 25 J/s of electrical energy and wastes 9 J/s of heat energy?

[ ]	278%
[ ]	36%
[ ]	0.36%
[x]	64%

It is important to remember that efficiency is a measure of the useful energy transfer. The way the question is worded could make you forget that the calculation gives you the percentage of energy that has been wasted and needs to subtracted from 100% to find the efficiency. Watch out for this sort of question in your exams

8.

Burning 2kg of wood in a particular woodburning stove releases 29 MJ of heat energy. If 25 MJ of that heat is transferred to the room, which of the following statements is true?

[ ]	The fire is 100% efficient
[ ]	The fire is between 90% and 100% efficient
[x]	The fire is between 85% and 90% efficient
[ ]	The efficiency of the fire is less than 85%

The efficiency is 25 ÷ 29 x 100 = 86.2% efficient

9.

Distributing electrical energy through the 400,000 V cables of the National Grid wastes some of the energy of the electricity (see below). What is the efficiency of this part of the system to the nearest whole number?

Total power generated: 62,161.5 MW
Step-up transformer losses: 157 MW
Step-down transformer losses: 142 MW
Losses caused by heating of the cables during transmission: 1.4%

[ ]	99%
[x]	98%
[ ]	97%
[ ]	96%

The total energy transfer losses are 1.87% so to the nearest whole number that is 2% wastage, leaving 98% efficiency. Efficiency is worse in the lower voltage sections of the National Grid because the higher currents cause more energy loss as heat

10.

A roof receives 1,000 W/m² of energy from the Sun on a clear, sunny day. How many watts would be produced from a 5cm wide by 20cm long solar cell positioned on the roof if the efficiency of the solar cell is 14%?

[x]	1.4 W
[ ]	1.6 W
[ ]	14,000 W
[ ]	14 kW

This question could look very complicated at first. The knack is to break down complicated questions into smaller parts which makes them more manageable. So, first you need to work out the area of the solar cell which is 0.1 m². That means that it receives 100 W of the insolation (incoming solar energy). Finally, rearranging the equation for efficiency provides the answer:
(efficiency x input wattage) ÷ 100 = output wattage