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Energy - Transfers and Efficiency

Every device you use transfers energy. This GCSE Physics quiz explores useful energy, wasted energy, and why efficiency matters for light bulbs, phone chargers, and more.

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Fascinating Fact:

Wasted energy is the part that spreads out and is difficult to use again, for example heat from a phone charger.

In GCSE Physics, you learn how energy is transferred from one store to another in real devices. By comparing useful and wasted energy, you can calculate efficiency and explain why some appliances cost more to run than others.

Key Terms

Energy transfer: The movement of energy from one store, or place, to another, such as electrical energy becoming light and heat in a lamp.
Useful output energy: The part of the transferred energy that appears in the form you actually want, for example light from a bulb or kinetic energy in a moving motor.
Wasted energy: Energy that is not useful for the intended purpose and usually spreads into the surroundings, often as unwanted heat or sound.

Frequently Asked Questions (Click to see answers)

What are useful and wasted energy in an energy transfer?

Useful energy is the energy that appears in the form you want, such as light from a lamp. Wasted energy is the energy that spreads to the surroundings and cannot easily be used again.

How do I calculate efficiency for my GCSE Physics exam?

To calculate efficiency, divide the useful output energy by the total input energy. You can then multiply this value by 100 if you need the efficiency as a percentage.

Why are efficient appliances important in everyday life?

Efficient appliances transfer a larger fraction of input energy usefully and waste less as heat or sound. This reduces energy bills, saves resources, and helps lower environmental impact.

Try These Related Quizzes

1 .

A wind turbine generates 100 joules of electricity from a gust of wind which has 300 joules of energy. How efficient is the turbine?

10%

33%

50%

66%

Wind turbines are an example of renewable energy

2 .

Which formula can be used to calculate the percentage of energy transferred by a device?

Energy Transferred = ^{Useful Energy Output}⁄_{Total Energy Input} x 100

Energy Transferred = ^{Total Energy Input}⁄_{Useful energy output} x 100

Energy Transferred = ^{Useful Energy Output}⁄_{Total Energy Input} x 10

Energy Transferred = ^{Total Energy Input}⁄_{Useful energy output} x 10

This is called the efficiency of an energy transfer

3 .

During an energy transfer, only part of it may be usefully transferred. What happens to the remainder of the unused energy?

It's wasted

All the energy is all transferred and used successfully

It is converted into carbon

It becomes a gas

In every energy transfer, some energy is wasted

4 .

What cannot be done to energy?

Created or destroyed

Dissipated

Transferred

Stored

It is impossible to create or destroy energy. In a science lesson, you may have watched a balloon being popped - all of the elastic energy within the balloon is transferred into sound, heat and kinetic energy

5 .

What happens to wasted energy?

It decomposes into the ground

It becomes hot

No energy is ever wasted

It is transferred into its surroundings

Any energy wasted by a process will always dissipate into its surroundings. Although it is still there, because it is so spread out, it makes it much more difficult to use

6 .

What can be done to energy?

It can be transferred

It can be stored

It can be dissipated

All of the above

Not all forms of energy can be stored

7 .

Calculate the efficiency of a heater which can convert 700 joules of chemical energy into 175 joules of heat energy.

10%

25%

35%

50%

Remember, efficiency is normally given as a percentage

8 .

A solar panel is 20% efficient at converting light energy into electricity. If it generates 200 joules of electrical power, how much power is wasted?

500 J

750 J

800 J

1000 J

This is an alternative way for the examiners to check your understanding of efficiency

9 .

An LED converts around 80% of the energy supplied to it into light. How much energy is converted into light if a total of 50 J is supplied to it?

30 J

40 J

50 J

60 J

LEDs are a much more efficient way of transferring electrical energy into light energy than the conventional filament bulb and fluorescent lamps ~ they last longer too

10 .

Which formula can be used to calculate the percentage of power transferred by a device?

Power Transferred = ^{Useful Power Output}⁄_{Total Power Input} x 100

Power Transferred = ^{Total Power Input}⁄_{Useful Power Output} x 100

Power Transferred = ^{Useful Power Output}⁄_{Total Power Input} x 10

Power Transferred = ^{Total Power Input}⁄_{Useful Power Output} x 10

More efficient devices waste less energy

You can find more about this topic by visiting BBC Bitesize - Energy

Author: Martin Moore