Heat transfer

Question 1

What are some different factors that effect the rate of heat transfer?

Answer 1

The size of the surface area.
Fins.
The type of material.
If the materials in contact with it are insulators and conductors.

Question 2

Are metals good conductors of heat?

Answer 2

Yes

Question 3

What are bad conductors of heat called?

Answer 3

Insulators

Question 4

Gas particles:

Answer 4

Almost no forces
Particles have more energy
Free to move
Random directions 
High speed

Question 5

Liquid particles:

Answer 5

Weaker forces
Particles  are  close together
Can move past each other
Have more energy than solids 
Move at low speeds

Question 6

Solid particles:

Answer 6

Strong forces
Particles are close together
Fixed pattern
Can only vibrate about their fixed position

Question 7

What do fins in and engine do?

Answer 7

Increase surface area to speed up cooling.

Question 8

If two objects at the same temperature have the same surface area but different volumes, which one will cool more quickly?

Answer 8

The one with the smaller volume.

Question 9

Give an example of how an animal controls heat transfer.

Answer 9

Arctic foxes: small ears
small surface area to minimise heat loss
by radiation.
Desert foxes: huge ears
large surface area to allow them to loose
heat loss by radiation.

Question 10

Describe how a vacuum limits heat transfer.

Answer 10

The glass bottle is double-walled with a vacuum between the two walls to stop conduction and convection through the sides.

Question 11

Heat energy is transferred from the heater coils to the what?

Answer 11

Water (conduction)

Question 12

The particles near the coils get ___________ so they start moving around faster

Answer 12

More energy

Question 13

Heating a room with a radiator relies on?

Answer 13

Convection currents

Question 14

Hot, less dense air by the radiator what flows to replace it?

Answer 14

Denser, cooler air

Question 15

Convection simply cant happen in solids because ….

Answer 15

particles cant move

Question 16

What happens when Gas cools?

Answer 16

The particles in the gas slow down and lose kinetic energy

Question 17

How does water vapour condense?

Answer 17

It condenses in the air when it comes into contact with cold surfaces

Question 18

Why does invisible water vapour condense?

Answer 18

It condenses to form tiny water droplets as it spreads into cooler air

Question 19

What is Condensation?

Answer 19

When a Gas turns to a Liquid

Question 20

What is Evaporation?

Answer 20

When a Liquid turns to a Gas

Question 21

What is melting?

Answer 21

When a solid turns to a liquid

Question 22

What is freezing?

Answer 22

When a liquid turns to a solid

Question 23

What is sublimation?

Answer 23

When a solid turns straight away to a gas (the liquid part is skipped out)

Question 24

In order for a solid to turn into a liquid and a liquid to turn into a gas what needs to happen to the particles?

Answer 24

The particles need to gain more kinetic energy (in order to break bonds)

Question 25

What state of matter has the most kinetic energy within its particles?

Answer 25

A Gas

Question 26

What state of matter has the least kinetic energy within its particles?

Answer 26

A Solid

Question 27

Explain the process of conduction

Answer 27

~ In conduction, one particle gets heated up and passes on its kinetic energy to it's neighbouring particle (and so on...)

Question 28

Why do metals make good conductors?

Answer 28

The metal contains free ions (electrons) which whizz around quickly and pass on the kinetic energy to random particles

Question 29

What do draught excluders do?

Answer 29

They are placed at the bottom of doors to minimise cold draughts by CONVECTION CURRENTS

Question 30

What does Double Glazing do?

Answer 30

It is an extra layer of glass placed in a window to minimise heat loss by CONDUCTION

Question 31

What do cavity walls do?

Answer 31

They are an additional layer of brick placed in walls to reduce heat loss by CONDUCTION

Question 32

What is Cavity Wall Insulation?

Answer 32

Foam placed in between cavity walls to reduce heat loss by CONVECTION

Question 33

What do radiator reflectors do?

Answer 33

They are a piece of shiny foil placed behind radiators to reflect the heat back into the home

Question 34

What is loft insulation?

Answer 34

A thick layer of fibreglass wood laid out across the floor and ceiling of the loft which reduces heat loss by CONDUCTION AND CONVECTION

Question 35

What do thick curtains do?

Answer 35

They are big bits of cloth over the window which reduces heat loss by CONDUCTION AND RADIATION

Question 36

What is the formula for Payback Time?

Answer 36

Payback time = initial cost/annual saving

Question 37

If the initial cost for installing loft insulation was £200 and the annual saving was £50. What would be the payback time?

Answer 37

200/50 = 4 years

Question 38

What is payback time measured in?

Answer 38

Years (sometimes can be months e.g. 15/30 can equal to 6 months)

Question 39

The better the insulator the (.......) the U-Value?

Answer 39

Lower