1.1 - Heat Transfer Flashcards
What do all objects do?
Emit and absorb infrared radiation
How does temperature effect the amount of infrared radiation emitted?
The hotter an object is the more infrared radiation it radiates
How do dark, matt surfaces effect radiation?
Good absorbers and good emitters of infrared radiation
How do light, shiny surfaces effect infrared radiation?
Poor absorbers, poor emitters and good reflectors of infrared radiation
In a hot country what colour would they paint the house to limit temperature inside?
White
What colour should radiators be painted to maximise heat to the room?
Black matt as it would be better at absorbing and emitting the heat to a room
What is the kinetic theory?
It explains the properties of the different states of matter
Describe a solids properties
Fixed and close regular patterns Vibrate on a fixed position Compact Dense Strong bonds Large resistance Large volume Can't compress
Describe a liquids properties
Slightly random pattern Vibrating moderately The bonds are together but not as strong Some resistance Can't compress Takes the shape of container as particles move around each other
Describe a Gases properties
Lots of space between particles Vibrates a lot Travel at a thousand miles per second Minimal resistance Minimal to no existent bonds Easy to compress
What is the main difference between solids, liquids and gases?
They all have different amounts of energy
What is conduction
Heat transfer through solids
How does conduction work?
In metals there are delocalised electrons that surround positive ions
The electrons gain kinetic energy when heated vibrating faster
The electrons collide with each other transferring the kinetic energy
What name is given to a material that allows electrical currents to pass through?
A conductor
Why don’t non-metals conduct electricity?
They don’t have delocalised electrons
What is a material called if they don’t conduct electricity?
Insulator
How does the start of convection work?
When you place a heat source next to the particles
As the particles gain kinetic they vibrate more
The space between the particles expands
As a result the area is less dense and the volume increases
The substance rises
How does the second part of convection work?
As the particles move further away from the heat source they lose energy
They become denser and the volume decreases
Pushed round by other particles the denser particles fall back down
How does liquid go to a gas?
Evaporation
What is evaporation?
As the liquid gets heated up the particles gain kinetic energy
They vibrate more and the space between the particles expands
With enough energy the bonds can be broken and and they start to move around independently
With a lot of energy they can escape becoming a gas
What happens to a liquid once some of it has evaporated?
It is cooler and have a lower average kinetic energy
Because when the particles leave they take the heat energy with them
At what point does evaporation happen the quickest?
Boiling point
What is an example of evaporation to cool something down?
Sweat
As it takes the heat energy away from your skin
What are the three factors affecting evaporation?
Surface area
Breeze or air moving over the surface
Heat
How does gas go to a liquid?
Condensation
What is condensation?
As the gas is cooled the kinetic energy of the particles is reduced
The decrease in movement closes the gaps between the particles
When they get closer together the bonds become stronger
What happens to energy during condensation?
It is released into the surrounding atmosphere
What are the factors affecting condensation?
Surface area
Temperature of the gas
What are the general factors that affect heat transfer?
Surface area
Volume
The type of material
The bigger the temperature difference between an object and its surroundings….
The faster the rate of energy is transferred
What is radiation transfer?
The type of transfer that doesn’t require particles i.e a vacuum
What are U-values?
They measure how affective a material is as an insulator
If you have a small U-value is the material a good or bad insulator?
A good insulator
Name 4 types of insulation in a house?
Cavity wall insulation
Fibre glass loft insulation
Double glazing windows
Draught proofing
