Conduction, Convection and Radiation

Question 1

What is heat?

Answer 1

Heat is thermal energy.

Question 2

How can heat be transferred from one place to another?

Answer 2

Heat can be transferred from one place to another by convection and conduction.

Question 3

How can energy be transferred?

Answer 3

Energy can be transferred by conduction, convection, and radiation.

Question 4

What is insulation used to stop?

Answer 4

Insulation is used to stop heat energy transfer from buildings and the human body.

Question 5

Why are liquids and gases ‘fluids’?

Answer 5

They can be made to flow. The particles in these fluids can move from place to place.

Question 6

When does convection occur?

Answer 6

When particles with lots of heat energy in a liquid or gas move and take the place of particles with less heat energy.

Question 7

What happens to liquids and gases when they are heated?

Answer 7

They expand.

Question 8

Why do liquids and gases expand when heated?

Answer 8

The particles in liquids and gases move faster when they are heated than they do when they are cold.

Question 9

How can heat be transferred?

Answer 9

Infrared radiation.

Question 10

What type of radiation is infrared radiation?

Answer 10

Unlike conduction and convection - which need particles - infrared radiation is a type of electromagnetic radiation that involves waves.

Question 11

Why can radiation work through the vacuum of space?

Answer 11

No particles are involved. This is why we can still feel the heat of the sun even though it’s 150 million km away from the earth.

Question 12

What surfaces are good absorbers and emitters of infrared radiation?

Answer 12

Dull, matt or rough surfaces.

Question 13

What surfaces are poor absorbers and emitters of infrared radiation?

Answer 13

Shiny surfaces. However, they are good reflectors of infrared radiation.

Question 14

Why are domestic radiators thin and flat?

Answer 14

If two objects made from the same material have identical volumes, a thin, flat object will radiate heat energy faster than a fat object.

Question 15

How do radiators transfer most of their heat?

Answer 15

Despite their name, radiators actually transfer most of their heat energy to a room by convection, not radiation.

Question 16

How is heat energy transferred from homes?

Answer 16

By conduction through the walls, floor, roof and windows. It is also transferred from homes by convection.

Question 17

How does heat energy leave the house?

Answer 17

By radiation - through the walls, roof, and windows

Question 18

List four ways to reduce heat loss:

Answer 18

• Fitting carpets, curtains,and draught excluders. It is even possible to fit reflective foil in the walls or on them.
• Heat loss through windows can be reduced by using double glazing. These special windows have air or a vacuum between two panes of glass
• Heat loss through walls can be reduced using cavity wall insulation. This involves blowing insulating material into the gap between the brick and the inside wall.
• Heat loss through the roof can be reduced by laying loft insulation. This works in a similar way to cavity wall insulation.

Question 19

What does conduction and convection involve?

Answer 19

Conduction and convection involve the transfer of energy by particles.

Question 20

What is the main form of heat transfer in solids?

Answer 20

Conduction

Question 21

What is the main form of heat transfer in liquids and gases?

Answer 21

Convection

Question 22

What can infrared radiation be emitted by?

Answer 22

Solids, liquids and gases.

Question 23

Can any object absorb and emit infrared radiation?

Answer 23

Yes, any object can both absorb and emit infrared radiation, whether or not conduction or convection are also taking place.

Question 24

What is infrared radiation emitted from?

Answer 24

The surface of an object. All objects are continually emitting and absorbing infrared radiation.

Question 25

What type of surfaces will reflect IR radiation?

Answer 25

Light, shiny surfaces

Question 26

What types of surfaces will absorb IR radiation?

Answer 26

Dark, matt surfaces

Question 27

What allows liquids and gases to transfer heat by convection?

Answer 27

Liquids and gases are usually free to move about - and that allows them to transfer heat by convection which is a much more effective process than conduction

Question 28

When does convection occur (2)?

Answer 28

Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them.

Question 29

Why can’t convection happen in solids?

Answer 29

The particles can’t move.