Thermal Energy Transfers

Question 1

What does energy transfer by conduction through a material depend on?

Answer 1

Thermal conductivity

Question 2

What is thermal conductivity?

Answer 2

Thermal conductivity is a measure of how well a material conducts energy when it is heated.

Question 3

A good insulator has a ____ thermal conductivity?

Answer 3

low

Question 4

The energy transfer per second through a layer of insulating material depends on:

Answer 4

1. Temperature difference across the matieral
2. Material thickness
3. Thermal conductivity of the material

Question 5

What is infrared radiation and where is it emitted from?

Answer 5

Infrared radiation is a part of the electromagnetic spectrum of waves, it is one of many types of electromagnetic radiation emitted from the sun.

Question 6

All objects, no matter their temperature…

Answer 6

emit and absorb infrared radiation.

Question 7

An object at constant temperature…

Answer 7

emits and absorbs infrared radiation at the same rate

Question 8

What are the 3 ways that heat can be transferred? (+states of matter)

Answer 8

1. Conduction (solids)
2. Convection (liquids and gases)
3. Raditiation (vacuum / gases)

Question 9

The bigger the temperature difference between hotter and cooler places…

Answer 9

the faster the energy transfers

Question 10

Compare solids, liquids, gases and vacuums as conducturs

Answer 10

1. Solids are the only material that can be good conductors
2. Liquids and gases are insulators
3. Conduction cannot happen in a vacuum

Question 11

why are solids the best conductors?

Answer 11

Because their particles are closely packed

Question 12

Why are metals such good conductors?

Answer 12

Because they have free electrons, these can move around freely, bumping into lots of particles, causing them to vibrate as well

Question 13

What is conduction?

Answer 13

Conduction is the process where vibrating particles transfer energy to neighbouring particles

Question 14

What is cold?

Answer 14

the absence of heat

Question 15

Why is air a good insulator?

Answer 15

because the particles in air are far apart and therefore can’t vibrate and pass energy to neighbouring particles like solids.

Question 16

Why is a vacuum a good insulator?

Answer 16

Vacuums have no particles meaning there is no medium for the energy to pass through = no transfer

Question 17

What is convection?

Answer 17

Convection is where energetic particles move away from hotter to cooler regions

Question 18

What happens when you heat a region of a gas or liquid? What does this do to it’s density?
What does this mean?

Answer 18

The particles move faster and the space between individuals particles increases
This decreases the the density of the region being heated
Liquids and gases can flow, so the warmer less dense regions rise above the cooler denser regions, if there is a constant heat source, a convection current can be created

Question 19

What is the name for the waves (radiation) that travel to us from the sun?

Answer 19

infrared electromagnetic waves

Question 20

What colour absorbs and emits radiation the best?

Answer 20

matt black materials

Question 21

What colour absorbs and emits radiation the worst

Answer 21

shiny white/silver materials - they reflect heat

Question 22

What factors make a material transfer heat well? (4)

Answer 22

1. large surface area (big ears - animals + radiator fins)
2. Matt black colour (absorbs and emits radiation best)
3. Metal (transfers heat by conduction - close particles + free electrons)
4. Large temperature difference between object and environment

Question 23

What factors make a material transfer heat badly? (4)

Answer 23

1. Small surface area - less contact between object + surroundings
2. Shiny white/silver colours (reflects radiation)
3. Air pockets/vacuum/insulators - stops conduction from occurring
4. Small temperature difference makes heat transfer slower

Question 24

What are methods used to reduce energy loss in the home? (6)

Answer 24

1. Loft Insulation
2. Cavity walls and insulation
3. Draught proofing
4. Carpeting
5. Double glazed windows + curtains
6. Hot water tank jackets

Question 25

Loft insulation?

Answer 25

Fiberglass "wool" laid across loft floors reduces conduction through the the ceiling to the roof

Question 26

Cavity walls and insulation?

Answer 26

Two layers of brick with a gap between them reduces conduction, Insulating foam (with a very low thermal conductivity) traps layers of air to minimise convection

Question 27

Draught proofing?

Answer 27

Strips of foam and plastic around doors and windows stop air going out which reduces convection

Question 28

Carpeting?

Answer 28

Laid across a floor to reduce conduction

Question 29

Curtains and double glazed windows?

Answer 29

Thick curtains reduce conduction and radiation through the windows. Double glazing = two layers of glass with an air gap between to reduce conduction

Question 30

Hot water tank jacket?

Answer 30

Lagging such as fibre glass wool reduces conduction

Question 31

Why does having free electrons mean metals are good conductors?

Answer 31

The movement of the free electrons means the transfer of energy or current happens quicker than simply from particle to neighbouring particle, making metals good conductors

Question 32

Why does large surface area mean a good heat transfer?

Answer 32

Large surface area means more particles exposed to the environment or object that heat is being transferred too. This means more particles are transferring heat at the same time = a good heat transfer