2. Transfer of heatof heat
Heat
• A form of energy.
• Travels from a hotter region to a colder region until
both regions are of the same temperature.
• Transferred from a warmer to a colder region in three
different ways:
Conduction
Convection
Radiation
3. What is convection?
ConvectionConvection
• The transfer of heat by the circulation of currents
from one region to another in a fluid (liquid or a
gas).
• Convection above a hot surface occurs because
hot air expands, becomes less dense, and rises.
• Hot water is likewise less dense than cold water
and rises, causing convection currents which
transport energy.
4. Examples of convection:
Example 1
Heated water in the pot expands and becomes
less dense.
The warmer water will then rises while the cooler
and denser water near the surface descends.
Convection currents are formed.
5. Example 2
Atmospheric convection
Atmospheric convection is a very important
part of Earth’s weather.
In atmospheric convection,
Warm air moves upwards.
Cool air falls downwards.
6. Example 3
Coal mines
When a fire was lit up at the bottom,
Hot air expands, becomes less dense, and
rises.
Cooler air from outside the coal mines enter the
mines to take the place of the leaving air.
Mines were thus ventilated with continuous supply
7. Natural and forced convectionNatural and forced convection
Natural convection
• It is caused by buoyancy forces due to density
differences caused by temperature variations in
the fluid.
Eg.
The buoyancy forces caused density
differences in the air inside the room
thus, convection occurs.
8. Forced convection
• In forced convection, fluid is circulated by a plump or
blower.
Eg.
In human circulatory system, a heart is
needed to pump the blood to other parts of
the body.
9. • Appliances such as
kettles,heaters,air-
conditioners and
refrigerators make use
of convection to heat
up or cool down liquids
or gases rapidly.
Applications of convection
10.
11. What are the three different ways
of Heat Transfer?
Ans :
Convection , Conduction &
Radiation
12. What is convection ?
Ans :
It is the transfer of heat by
the circulation of currents
from one region to another in a
fluid (liquid or a gas).
13. What is the function of
convection current?
Ans :
Convection current transports energy.
14. What are the two types of
convection?
Ans :
They are natural convection and forced
convection.
