P2- Heat transfers

Question 1

Describe the experiment to test different materials as conductors

Answer 1

Use a rod of each different material.
Coat the end of each rod with a thin layer of wax.
Heat the non-waxed ends of each rod together, at the same time.

The rod whose wax melts the fastest is the best conductor of heart.

Question 2

The energy transfer by conduction through a material depends on what?

Answer 2

Its thermal conductivity.

Question 3

What is an insulator?

Answer 3

A material which has a low thermal conductivity

Question 4

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

Answer 4

The temperature difference across the material
The material’s thermal conductivity
The material’s thickness

Question 5

Why do the rods need to be equal in length and diameter?

Answer 5

So the investigation will be fair

Question 6

To reduce the energy transfer as much as possible what should happen?

Answer 6

Thermal conductivity of insulating material should be as low as possible
Thickness of insulating layer should be as thick as practically possible

Question 7

What forms of radiation are emitted by the Sun, which can pass through the Earth’s atmosphere?

Answer 7

Infrared radiation and Visible Light

Question 8

Infrared radiation and visible light are both emitted by the Sun. They are both parts of what?

Answer 8

The electromagnetic spectrum

Question 9

All objects emit what type of radiation?

Answer 9

Infrared radiation

Question 10

What is a perfect black body?

Answer 10

A body which is a perfect absorber and emitter of radiation.

Question 11

What does a black body NOT do?

Answer 11

Transmit or reflect radiation

Question 12

What is black body radiation?

Answer 12

The radiation emitted by a black body

Question 13

When an object emits and absorbs infrared radiation at the same rate, what happens to its temperature?

Answer 13

It is constant

Question 14

What type of surface is the best at emitting radiation?

Answer 14

Matte black surfaces

Question 15

What type of surface is the least effective at emitting radiation?

Answer 15

Shiny light surfaces

Question 16

How does global warming work?

Answer 16

Sun emits infrared radiation towards the Earth
IR heats up the Earth
Earth emits IR towards space
Greenhouse gases trap the IR
Greenhouse gases re-emit the IR back towards the Earth’s surface
Some of the IR is emitted towards outer space
Heats the Earth up again
CYCLE REPEATS

Question 17

How does more greenhouse gases effect global warming?

Answer 17

More IR is being trapped in the Earth’s atmosphere
Less IR escapes from the Earth
The Earth is being heated more and more as greenhouses gases in the atmosphere increase

Question 18

When a substance is heated, its temperature rise depends on what?

Answer 18

The amount of energy supplied to it
Mass of the substance
What the substance is

Question 19

What is the specific heat capacity of an object?

Answer 19

The amount of energy required to heat up 1kg of the object by 1 degree Celcius

Question 20

How does fibreglass loft insulation work?

Answer 20

Reduces rate of energy transfer through the roof
Fibreglass is a good insulator.
Air between fibres helps to reduce the rate of energy transfer by conduction

Question 21

The greater the number of layers of insulation means?

Answer 21

The thicker the insulation, therefore the rate of energy transfer will be decreased

Question 22

How does cavity wall insulation work?

Answer 22

Reduces rate of energy transfer through the outer walls of the house
Cavity of an outer wall is the space between two layers of brick that make up the wall
Insulation is pumped into the cavity
It is a better insulator than the air it replaces
Traps the air in small pockets
Reduces rate of energy transfer by conduction

Question 23

How does aluminium foil between the wall and radiator work?

Answer 23

Reflects radiation away from the wall
Al foil is shiny and light
Reduces rate of energy transfer by radiation

Question 24

How does double-glazed windows work?

Answer 24

Two glass panes
Dry air / a vacuum between the panes
Dry air reduces rate of energy transfer by conduction
Vacuum reduces rate of energy transfer by convection

Question 25

The thicker the glass of double-glazed windows means?

Answer 25

The slower the rate of energy transfer by conduction

Question 26

Low thermal conductivity means?

Answer 26

Low rate of energy transfer

Question 27

How do solar panels work?

Answer 27

Absorb infrared radiation from Sun
Generates electricity directly
OR
Heats water directly (solar heating panels)