# Energy and Efficiency

In this worksheet, students will learn how energy can be saved and used efficiently as well as the calculation of efficiency.

Key stage:  KS 4

Curriculum topic:  Physics: Energy

Curriculum subtopic:  Calculating Energy Efficiency for Energy Transfers

Difficulty level:

### QUESTION 1 of 10

With the increased demands for energy around the world, especially in developed countries, it is really important to keep the use of energy as low as possible, so as to extend the life of fossil fuels (coal, oil and natural gas). This is cost-effective as well, as it decreases electricity bills. Alternative sources of energy are increasingly used, but this worksheet's focus is on the benefits of insulation and calculation of energy efficiency.

Homes lose energy from the roof, walls, doors, floors and windows, as shown in the diagram below:

This energy is wasted. as it goes into the environment. This means that the house needs more energy, in order for it to be warm enough to live in during cold periods. Hot air rises due to convection, so fibreglass is usually used to insulate the roof. Air is an insulator, which means it does not let heat go through. Fibreglass contains a lot of gaps, where air is trapped, keeping the heat inside the house. A coal fire would warm the room by radiation.

Double glazed windows are also used for insulation (they also help reduce noise pollution from busy streets). Double glazed windows are made of two panes of glass with air, argon or vacuum sandwiched between them. A vacuum does not contain any particles, so it is impossible for heat to be transmitted through it. Air and argon are good insulators because, as gases, their particles are far away from each other, so heat cannot be conducted from one particle to another.

Each energy source has its advantages and disadvantages. The most cost-effective type of insulation is the one that has the shorter payback time (measured in years). The formula for calculating it is:

It is also worth checking the efficiency of sources of heat. The formula for calculating efficiency is:

What is the general name of the precautions we take to reduce energy loss from home?

Insulation

Vacuums

What is the phenomenon that causes hot air to rise?

Convention

Convection

Contraction

How do radiators and coal fires transfer heat?

By convection

By insulation

What mediums are used in double glazing?

Water

Air

Argon

Nitrogen

Feathers

Vacuum

How is energy transferred in solids, where particles are close to each other?

By convection

By conduction

What is the main material used in roof insulation?

Fiberglass

Air

Feathers

Considering your answer to Question 6, why is that material a good insulator?

It has no gaps in it so it keeps heat in.

It has gaps in it, and the air trapped in them is a good conductor.

It has gaps in it, and the air trapped in them is a good insulator.

Calculate the payback time of double glazing that costs £3000 and ensures an annual saving of £50.

30 years

60 years

120 years

What is the efficiency (in percentage) of a radiator where, for every 500 J of energy, 100 J are transferred to the room? Use the formula from the introduction to help you (you can look at it again by clicking on the Help button).

2%

10%

20%

Using your common sense, tick the correct statement:

A fireplace is more efficient when placed in the centre of a room.

A fireplace is more efficient when placed near a wall.

• Question 1

What is the general name of the precautions we take to reduce energy loss from home?

Insulation
EDDIE SAYS
Insulation is used to reduce energy loss from homes. Vacuums are used within double glazed windows and radiation is created from coal fires.
• Question 2

What is the phenomenon that causes hot air to rise?

Convection
EDDIE SAYS
Convection is the collective movement of particles. Hot air rises as it is less dense and this is, therefore, a form of convection. Convection is where the things move!
• Question 3

How do radiators and coal fires transfer heat?

EDDIE SAYS
Radiators and coal fires transfer heat by radiation. This means that the heat can be moved directly to a spot where it is needed, even if it is below! This is because it is a type of wave, not traditional heat like in conduction and convection.
• Question 4

What mediums are used in double glazing?

Air
Argon
Vacuum
EDDIE SAYS
Air, argon and vacuum are used in double glazing. This is because they are all not very good at letting heat pass through them. This, in turn, keeps the heat from escaping through the windows.
• Question 5

How is energy transferred in solids, where particles are close to each other?

By conduction
EDDIE SAYS
Energy is transferred in solids by conduction, which is the process of heat moving from one particle to another.
• Question 6

What is the main material used in roof insulation?

Fiberglass
EDDIE SAYS
Fibreglass is the main material used in roof insulation. This is because it is able to trap small pockets of air and stop it from forming convection currents.
• Question 7

Considering your answer to Question 6, why is that material a good insulator?

It has gaps in it, and the air trapped in them is a good insulator.
EDDIE SAYS
Fibreglass a good insulator because it has gaps in it with air trapped inside the gaps and the air also acts as an insulator to keep warmth inside the house.
• Question 8

Calculate the payback time of double glazing that costs £3000 and ensures an annual saving of £50.

60 years
EDDIE SAYS
• Question 9

What is the efficiency (in percentage) of a radiator where, for every 500 J of energy, 100 J are transferred to the room? Use the formula from the introduction to help you (you can look at it again by clicking on the Help button).

20%
EDDIE SAYS

0.2 x 100 = 20% efficiency
• Question 10

Using your common sense, tick the correct statement:

A fireplace is more efficient when placed in the centre of a room.
EDDIE SAYS
A fireplace is more efficient when placed in the centre of a room, because more energy is transferred to the room this way, rather than being lost through the wall.
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