density, heat transfer and heat loss in homes

Question 1

what is density?

Answer 1

a measure of how much matter is present in a given volume

Question 2

what is the density of a solid like?

Answer 2

particles are very close together, tightly packed so they have a high density

Question 3

what is the density of a liquid like?

Answer 3

particles are close together, still tightly packed so have high density but less dense than solids

Question 4

what is the density of gas like?

Answer 4

particles are very far apart and so have a low density

Question 5

what is conduction?

Answer 5

flow of heat through a material, from places of high temperature to low temperature

Question 6

are metals good conductors?

Answer 6

yes

Question 7

are plastics, wood, fabrics and glass good conductors?

Answer 7

no

Question 8

what are bad conductors known as?

Answer 8

insulators

Question 9

how do metals conduct heat?

Answer 9

metals contain ‘free electrons’ which gain energy when they are heated. They then move into cooler regions and collide with atoms. Their energy is passed on and temperature rises

Question 10

what is convection?

Answer 10

flow of heat energy through a liquid or gas from a place of high temperature to low temperature

Question 11

how is a convection current set up?

Answer 11

how liquid/ gas increases in volume and becomes less dense and lighter because the particles move faster and further apart. The hot liquid/ gas will rise. The colder, denser and heavier liquid/ gas will fall and gets heated. A convection current is set up.

Question 12

what is radiation?

Answer 12

All hot or warm objects radiate heat in the form of infra-red radiation, the hotter the object the more heat energy it will emit

Question 13

what are good emitters or infra red radiation?

Answer 13

dark surface because no heat is reflected away

Question 14

what type of surface is a good absorber of heat radiation?

Answer 14

black surface

Question 15

are shiny surfaces good emitters and absorbers?

Answer 15

no but they are good reflectors

Question 16

why is it important to reduce heat loss?

Answer 16

saves money
reduces use of heating
reduces fossil fuel use
reduces pollution and use of fossil fuels

Question 17

where is heat lost in a house?

Answer 17

windows and doors
floors
walls
roof

Question 18

where is heat lost due to conduction?

Answer 18

walls, windows, floor and roof

Question 19

where is heat lost due to convection?

Answer 19

draughts

Question 20

where is heat lost due to radiation?

Answer 20

walls, roof and windows

Question 21

how do you reduce heat loss in the roof?

Answer 21

loft insulation - traps air between fibres, air is an insulator and therefore prevents conduction. Air is also trapped in pockets which stops convection currents being set up

Question 22

how do you reduce heat loss in windows?

Answer 22

double glazing - two panes of glass which trap air, air is an insulator and therefore prevents conduction. May be a vacuum between glass and this prevents conduction and convection

Question 23

how do you prevent heat loss in walls?

Answer 23

cavity walls - foam is inserted which traps air which therefore stops conduction and convection

Question 24

how do you prevent heat loss from draughts?

Answer 24

draught excluders - prevent flow of air and therefore convection currents

Question 25

how do you prevent heat loss in floors?

Answer 25

underlay - trap air reducing condcution

Question 26

how do you calculate payback time?

Answer 26

savings per year