C10 - Transfer of Heat Energy and It's Effects
Temperature
define
Measure of how hot an object is
SI Unit
Kelvin
0 degree Celsius = 273 Kelvin
0 Kelvin = -273 degree Celcius
Expansion and Contraction
when substance is heated...
particles vibrate/ move faster
particles are further apart
gains energy
density decrease
when substance is cooled...
loses energy
particles vibrate/ move slower
particles are closer together
density increases
Expands
Contracts
bimetallic strip
Two different metals that expands at different rates
when heated
brass expands more than iron, hence strip bends upwards
when cooled
brass contracts more than iron, hence strip bends downwards
The metal with a faster rate of expansion also has a faster rate of contraction.
heat transfer
Heat energy travels from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached.
3 methods of transfer
convection
radiation
conduction
define
is the transfer of heat energy without the physical movement of the medium.
good conductors
poor conductors
metals
plastics, fibres, wood, air
define
is the transfer of heat energy from one place to another by the physical movement of a medium. Fluids (liquids and gases) transfer heat energy mainly by convection.
explain how convection currents are formed
aircon unit is placed near the ceiling of the room
(1) Air around the air-con unit becomes cool, contracts, becomes denser and sinks to the bottom of the room.
2)Hot air at the bottom of the room, being less dense, rises and takes the place near the air-conditioner.
(3) Hence a convection current is set-up.
heating element in kettle is at the bottom
(1) Water near the heating element is heated up, expands and becomes less dense. It rises.
(2) Cooler water being more dense rushes down to take the place left by the heated water.
(3) Hence a convection current is set-up.
define
is the transfer of heat energy from a hotter body to a cooler body without the need for a medium.
emission and absorption of radiant heat
emission of radiant heat: gives off radiant heat (because surrounding is cooler)
absorption of radiant heat: takes in radiant heat (because surrounding is hotter)
factors affecting radiation
total surface area
temperature
colour and nature of surface
black/dull/rough
white/shiny/smooth
good emitter and absorber
poor emitter and absorber
larger surface area will be a better emitter and absorber
higher temperature will be a better emitter