hi viewers, this is Ishita Soni of class VII-B.I study in GD Goenka Public School. This is a knowledge sharing presentation on convection. Please have a quick glance on it so that i have a good response and experience so that i come up with more attractive presentations later. THNX

2. What is ConveCtion ???What is ConveCtion ???
The phenomenon due to which particles of a
medium actually move to the source of heat energy,
and then move away from it after absorbing heat
energy is called Convection . In simple words,
Convection is the mode of heat transfer
in fluids (liquids and gases).

3. More about ConveCtionMore about ConveCtion
Convection takes place in fluids only where molecules are free
to move about. Exception is mercury which gets heated by
conduction as it is a very good conductor of heat.
Convection depends on the fact that, in general, fluids
expand when heated and thus undergo a decrease in
density (since a given volume of the fluid contains less
matter at a higher temperature than at the original, lower
temperature). Now question rises that Why is convection not
possible in solids? The answer is that the molecules of a
solid are held tightly amongst each other due to
intermolecular forces. As, these molecules cannot travel to
the source of heat energy, convection is not possible in the
cases of solids.

4. What are convectionWhat are convection
currents???currents???
On heating, as a result, the warmer, less dense portion of theOn heating, as a result, the warmer, less dense portion of the
fluid will tend to rise through the surrounding cooler fluid, influid will tend to rise through the surrounding cooler fluid, in
accordance with accordance with Archimedes' principleArchimedes' principle. If heat continues to. If heat continues to
be supplied, the cooler fluid that flows in to replace thebe supplied, the cooler fluid that flows in to replace the
rising warmer fluid will also become heated and also rise.rising warmer fluid will also become heated and also rise.
Thus, a current, called a convection current, becomesThus, a current, called a convection current, becomes
established in the fluid, with warmer, less dense fluidestablished in the fluid, with warmer, less dense fluid
continually rising from the point of application of heat andcontinually rising from the point of application of heat and
cooler, denser portions of the fluid flowing outward andcooler, denser portions of the fluid flowing outward and
downward to replace the warmer fluid. In this manner, heatdownward to replace the warmer fluid. In this manner, heat
eventually may be transferred to the entire fluid. Convectioneventually may be transferred to the entire fluid. Convection
currents are widely observed in both currents are widely observed in both liquidsliquids and gases. and gases.
Many aspects of weather are connected with convectionMany aspects of weather are connected with convection
currents .currents .

5. images for convectionimages for convection
currentscurrents

6. applications of convectionapplications of convection
currents in gasescurrents in gases
• VentilationVentilation
• Sea breeze and land breezeSea breeze and land breeze

7. VentilationVentilation
The supplying of air motion in a space byThe supplying of air motion in a space by
circulation or by moving air through thecirculation or by moving air through the
space. It may include partial treatmentspace. It may include partial treatment
such as heating, humidity control, filteringsuch as heating, humidity control, filtering
or purification, and, in some cases,or purification, and, in some cases,
evaporative cooling. In simple words, theevaporative cooling. In simple words, the
process by which continuous replacing ofprocess by which continuous replacing of
warm and impure air by cool and fresh airwarm and impure air by cool and fresh air
from outside is calledfrom outside is called Ventilation.Ventilation.

8. How does Ventilation takesHow does Ventilation takes
place???place???
Breathing by people in a room causes increase inBreathing by people in a room causes increase in
the rate of moisture and carbon dioxide in air.the rate of moisture and carbon dioxide in air.
Moreover, the air gets warm. This warm air isMoreover, the air gets warm. This warm air is
light and hence rises up. It then passes out oflight and hence rises up. It then passes out of
the ventilators. This causes a fall in pressure inthe ventilators. This causes a fall in pressure in
the room. To make up for this fall in pressure thethe room. To make up for this fall in pressure the
cool air from outside flows in. Thus, the warm aircool air from outside flows in. Thus, the warm air
is continuously replaced by cool and fresh airis continuously replaced by cool and fresh air
that is Ventilation takes place.that is Ventilation takes place.

9. images for Ventilationimages for Ventilation

10. Sea BreezeSea Breeze
During day time, sun shines equally on theDuring day time, sun shines equally on the
land as well as the sea. However, the landland as well as the sea. However, the land
gets heated up faster than the sea as thegets heated up faster than the sea as the
specific heat capacity of the land is far lessspecific heat capacity of the land is far less
than the sea water. Thus, the air above landthan the sea water. Thus, the air above land
becomes hotter than the air above sea. Thisbecomes hotter than the air above sea. This
hot air being light expands and rises up.hot air being light expands and rises up.
This results in a fall of pressure over theThis results in a fall of pressure over the
surface of land .To make up for this fall insurface of land .To make up for this fall in
pressure cool air from sea starts blowingpressure cool air from sea starts blowing
towards land giving rise totowards land giving rise to SEA BREEZE.SEA BREEZE.

11. Land BreezeLand Breeze
During night, land as well as sea lose heat.During night, land as well as sea lose heat.
However, the land loses its heat more rapidlyHowever, the land loses its heat more rapidly
as compared to sea on the account of its lowas compared to sea on the account of its low
specific heat capacity. Thus the air abovespecific heat capacity. Thus the air above
land becomes colder than the air above sea.land becomes colder than the air above sea.
The hot air above sea being light expandsThe hot air above sea being light expands
and rises up .This causes a fall in pressureand rises up .This causes a fall in pressure
over the surface of the sea. To make up forover the surface of the sea. To make up for
this fall in pressure the air above land startsthis fall in pressure the air above land starts
blowing towards the sea giving rise toblowing towards the sea giving rise to LANDLAND
BREEZE.BREEZE.

12. ImageS for Land and SeaImageS for Land and Sea
BreezeBreeze