Heat Flashcards
(28 cards)
What is heat?
Heat is a form of energy. When a material is heated it gains energy and its particles move faster, therefore heat energy is seen in movement of particles
What is heat measured in?
Joules
What is temperature?
How hot or cold an object is.
How is heat related to temperature?
Heat is the energy needed to raise the temperature of an object or the energy lost when an object cools down.
What is temperature measured in?
Celsius (ºC) or Kelvin (K)
What has more thermal energy and why?
Cup of tea at 80oC or swimming pool at 30oC
Swimming pool - it has more water molecules so stores more thermal energy.
What are the 3 forms of heat transer?
Conduction
Convection
Radiation
What is conduction?
Transfer of heat energy through matter from places of higher temperature to places of lower temperature, without the movement of the matter
What is convection?
Flow of heat through a fluid (liquid or gas) from places of higher temperature to places of lower temperature by movement of the fluid itself.
What is radiation?
Transfer of heat energy from a place of higher temperature to a place of lower temperature by means of electromagnetic waves.
How does conduction work?
When something is heated it’s particles gain thermal energy causing them to vibrate more vigorously.
The particles bump in to nearby particles making them vibrate as well.
This passes the thermal energy through the object by conduction from the hot to the cold end.
Why is metal a very good conductor of heat?
Metals have many free electrons. These free electrons can travel through the metal transferring the heat more quickly.
How does convection work?
Convection happens due to hot liquid/hot gas expanding making it less dense.
Less dense liquid/gas rises causing convection currents.
These convection currents transport the energy.
How does radiation work?
Doesn’t need a medium i.e. can travel through a vacuum
Transfers at speed of light in straight lines
Every object which is at a temperature above it’s surroundings loses heat through radiation even people.
By what method does the heat from sun reach earth
Radiation as space is a vacuum i.e. it is empty and has not particles in it.
Where is most heat lost in a home
Walls
What percentage of heat is lost through the roof?
25
What can be used to reduce heat loss through the roof?
Loft Insulation - fibreglass ‘wool’ laid across the loft floor
Reduced conduction through ceiling into loft
Cost: 450, Annual Saving: 150
What percentage of heat is lost through walls?
35
What can be used to reduce heat loss through walls?
Cavity wall Insulation
Cavity wall -Two layers for brick with a gap between them reduce conduction
Insulation - Foam squirted into the gap trapping pockets of air to minimise convection
Cost: 500, Annual Saving: 100
What percentage of heat is lost through draughts?
15
What can be used to reduce heat loss through draughts?
Draught proofing - strips of foam and plastic around doors and windows stop air going out reducing convection.
Cost: 30, Annual Saving: 20
What percentage of heat is lost through floors?
10
What can be used to reduce heat loss through floors?
Carpet - reduce conduction
Cost: 400, Annual Saving: 40
