Conduction , Convection and Radiation.

1. Free Powerpoint Templates
Page 1
Heat
Transfer

2. Modes of Heat Transfer
Conducti
on
Convecti
on
Radiatio
n
Conduction is the transfer of thermal energy
through a substance , or between substances in
contact, by the collision of particles.
Conduction occurs in solids and liquids.
Convection is how the air contacted with heat
material, which takes it to other materials with
different temperatures.
Convection occurs in liquids and gases.
The process in which energy is transferred waves.
 It is the combined processes of
emission, transmission, and absorption of heat or
light.

3. CONDUCTION
Molecular
vibration
Free electron
diffusion
Occurs in all
solids
Slow process
Occurs in metals
only
Fast process
 Two types of conduction
 Molecular vibration
 Free electron diffusion
Conductors and Insulators
Materials that can conduct heat easily and
readily (eg. Metals) are known as conductors.
Materials that do not conduct heat easily (eg.
Water, air, plastic) are known as insulators.

4. What happens during
convection?
1
• Water at the bottom is heated first.
• Heated water expands.
2
• When water expands density decreases
• Heated water of lower density starts to rise.
3
• Cooler water of higher density rushes in from sides to
take its place.
• The cooler water gets heated and the cycle repeats.
Convection currents are set up.
Taking the example of heating water.
Convection

5. Hot water
rises
Cooler
water
sinks
Cools at
the
surface

6. Convection helps to make the Earth liveable as
it removes excess heat from the Earth and
transporting it high up into the atmosphere.

7. Page 7

8. Applications of convection.
Air con is usually placed at
the top of a room.
Heating coil of a kettle is
usually at the bottom
Formation of land and sea
breezes

9. Radiation
Radiation does not require a medium to
transfer heat. (can occur in a vacuum)
Sun releases electromagnetic waves (heat
is contained in the waves as infra-red)
Hotter objects radiates more heat.

10. Page 10
Emitters and absorbers
 The Sun gives out the heat.
 It is known as an emitter / radiator
 The Earth takes in the heat.
 It is known as an absorber.
 A good emitter would also be a good absorber.
 A poor emitter would be a poor absorber.
Good
emitter/absorber
Poor
emitter/absorber
Dull, black
surface
Rough surface
Shiny, silver
surface
Smooth surface

11. Done By :
Alefiya & Disha.