P2 - Heat Transfer

Question 1

What is Conduction?

Answer 1

Conduction is the heat transfer in solids e.g. the handle of a pan getting hot

Question 2

What is Convection?

Answer 2

Convection is the heat transfer in fluids (liquids, gases) e.g. convection currents in the mantle

Question 3

What is radiation?

Answer 3

A form of heat transfer where thermal energy (heat) is given out as infrared waves e.g. the sun heating up your face. Radiation can be reflected and happens is gases and vacuums

Question 4

What is thermal conductivity?

Answer 4

A measure of how well a material conducts thermal energy by conduction

Question 5

Process of convection currents

Answer 5

Air is heated. As it warms, it’s density decreases. The warm air rises and cooler denser air takes its place. A convection current is set up and will heat all the air in the room eventually

Question 6

Definition of absorb

Answer 6

To take something in (e.g. heat)

Question 7

Definition of reflect

Answer 7

To make something bounce back

Question 8

Definition of radiate

Answer 8

To give out something

Question 9

Definition of transmit

Answer 9

To move through

Question 10

Worst emitter, absorber, best reflector

Answer 10

Shiny white, silver

Question 11

Matt and shiny comparison

Answer 11

Matt is dispersed over a larger area due to a more rough surface. Shiny reflects waves straight away.

Question 12

What is black body and black body radiation?

Answer 12

A black body is a theoretical object that absorbs all the light that hits it so appears perfectly black when cold. Black body radiation is the radiation emitted by it.

Question 13

What is specific heat capacity?

Answer 13

The thermal energy needed to raise the temperature of 1 kg of a substance by 1 °C

Question 14

What is infrared radiation?

Answer 14

electromagnetic waves between visible light and microwaves in the electromagnetic spectrum

Question 15

Change in thermal energy (J) equals…

Answer 15

mass (kg) × specific heat capacity (J/kg °C) × change in temperature (°C)

Question 16

°C to K

Answer 16

+273

Question 17

How does loft insulation work?

Answer 17

Loft insulation such as fibreglass contains trapped air and so forms an insulating layer between the loft and the rest of the house. This helps to reduce heat loss through the roof.

Question 18

How does cavity wall insulation work?

Answer 18

In between 2 layers of bricks there is a cavity. The air trapped in the cavity acts as an insulator and reduces any heat loss due to conduction through the bricks. Heat loss can also occur due to convection within the cavity. Foam insulation can be pumped into the cavity to prevent this.

Question 19

How does double glazing work?

Answer 19

Double glazing adds an extra pane of glass. The air trapped between the two panes acts as an insulator and reduces heat loss by conduction.

Question 20

Hows does foil behind radiators work?

Answer 20

Heat loss from a radiator can be reduced by placing shiny foil between the wall and the radiator. The foil prevents heat radiation from reaching the wall by reflecting it back into the room.

Question 21

How do draught excluders work?

Answer 21

Draught excluders are hairy or spongy strips that can be used to close the gaps around doors and windows to prevent air from convection currents escaping (draughts)

Question 22

How do curtains work?

Answer 22

Fitting curtains and closing them can prevent draughts leaving a house and so reduce heat loss.

Question 23

How do you calculate payback time?

Answer 23

Total expenditure / annual saving

Question 24

Explain The Greenhouse effect

Answer 24

The atmoshpere prevents the suns radiation from leaving and reflects it back to the earth, making it warmer

Question 25

Impacts of greenhouse effect

Answer 25

Sea level rises, more frequent storms, rainfall patterns change

Question 26

Heat balance

Answer 26

A system stays at a constant temperature if the same amount of energy is absorbed than emitted.

Question 27

Peak intensity, wavelength

Answer 27

Longer the wavelengh, the lower the peak intensity