Heat Transfer Test 2 Y10 Flashcards
Heat always moves from…
Hot to cold
Heat is also known as
Thermal
3 methods of heat transfer are;
1) conduction
2) convection
3) radiation (infra red)
Explain conduction
1) only happens in solids
2) molecules vibrate about a fixed position.
3) They have kinetic and potential energy. (These are called internal energy)
What happens if a material is heated (conduction)
1) Then the kinetic and potential energy increases, the particles vibrate faster and further.
2) The energy is passed along the material from particle to particle.
Good conductors:
Metals
Bad conductors:
Non- metals
Why are metals good conductors …
Metals have free electrons, that can move colliding with the fixed particles, making them vibrate more
Convection occurs in:
Gases and liquids
Explain convection
1) the water above the heat source gets hot and it expands (particles move away from one another)
2) the water becomes less dense, and it rises
3) it gives the energy away, becomes more dense and sinks.
!This continues and is called a convection current!
Explain radiation
Take a marshmallow. It can’t be heated by conv. or cond., so it has to be radiation.
Heat radiates from a hot object in straight lines.
Black is a good absorber of heat.
Black is the best emitter of radiation.
Silver is a bad absorber (it reflects the heat).
Silver is the worst emitter of radiation.
How to reduce heat loss in …
Conduction
1) use a poor conductor
How to reduce heat loss in …
Convection
1) stop the particles moving or remove them (vacuum)
2) many systems trap air/ water to stop the convection current. Eg- wetsuit, layers of clothing, thermals)
How to reduce heat loss in …
Radiation
1) silver the surface (poor emitter)
Specific heat capacity;
1) This is the heat required to raise the temp. of 1kg of material by 1°C.
Eg/ water—> c= 4200J/kg°C
