This document discusses the three main methods of heat transfer: conduction, convection, and radiation. Conduction involves the transfer of thermal energy between molecules in direct contact. Convection involves the transfer of heat by the circulation of fluids like gases and liquids. Radiation involves the emission and absorption of electromagnetic waves and can occur through a vacuum. Various materials are classified as good or poor conductors based on their ability to transfer heat via conduction. Insulators are poor conductors that reduce heat transfer. Convection examples include ocean currents and heating/cooling systems. Radiation examples demonstrate how color affects heat absorption and emission. Proper insulation of homes reduces heat loss or gain.

1. TRANSFER OF
THERMAL ENERGY

2. CONDUCTION
Conduction is the process by which heat is
transmitted through a medium from its hotter part
to its colder part until they are both at the same
temperature.
Conduction occurs only in solid.
Explanation:
• Molecules in a solid are arranged very close to
each other.
• When one end of the metal rod is heated, the
molecules at this end vibrate faster due to the
increased kinetic energy.
• The molecules collide with the neighboring
molecules and cause them to vibrate faster.
• This process is repeated until the molecules of the
rod at the other end vibrate faster.
• Thus heat has been transferred from one end of

4. THERMAL CONDUCTORS
Materials which allow heat to flow through it well are
called thermal conductors.
Examples: copper, Aluminum, iron, gold etc….
THERMAL INSULATORS
Materials which do not allow heat to flow through it
well are called thermal insulators or poor conductors.
Examples: Glass, Water, Plastics, Rubber, Wood etc..
Materials containing air (wool, fiberglass,
plastic foam, expanded polystyrene)

5. Diagram below shows one way to compare different
metals. The metal rods are all the same size. Each has
a blob of wax at one end. They all heated equally at
the other end. The best conductor is the metal on
which the wax melt first.
COMPARING THERMAL CONDUCTORS

6. Procedure
1. Set up the apparatus as shown in the diagram.
2. Heat the water at the top of the test tube gently to
boil the water.
Observation & conclusion
1. The water at the top of the test tube boils while water
at the bottom of the test tube remains cold and the
ice does not melt.
2. The experiment shows that water is a bad conductor
TO SHOW THAT WATER IS A BAD CONDUCTOR OF HEAT

7. Examples of everyday application:
1. All metals are good conductors of heat. So cooking
pans, kettles, electric iron are made of copper,
aluminum or steel.
2. Plastic and wood are poor conductors (good
insulators). Therefore handles of cooking utensils are
made of plastics or wood.
3. Air is a very good insulator. So if a substance
contains a layer of trapped air, it can stop the
conduction of heat. For example, wool keeps you
warm because it traps a lot of air. The air trapped in
and between our clothes and blankets keeps us warm.
4. In the same way, the air trapped in fur and feathers
keeps animals warm. Birds fluff up their feathers in
winter to trap more air.

8. CONVECTION
Convection is the process by which heat is transferred
from one place to another by the movements of heated
particles of a gas or liquid.
Convection can only occurs in fluid (liquid and gas)
CONVECTION IN LIQUID
In the experiment below, the bottom of the beaker is
being gently heated in one place only. As the water
above the flame become warmer, it expands and
become less dense. It raises upwards as cooler, dense
water sinks and displaces the less dense water. The
result is a circulating stream, called convection current.
Where the water is heated, its particles circulate; they
transfer energy to the other parts of the beaker.

9. CONVECTION IN AIR
In the set-up shown in the diagram, smoke is been to
move through the box. The candle heats the air above it
and causes less dense air to rise, setting up convection
currents. The denser colder air is force into the box.

10. Examples of everyday application:
1. Heated by the sun, warm air rises above the equator
as it is displaced by the cooler, dense air sinking to
north and south. The result is huge convection
current in the Earth’s atmosphere. These cause
winds across all oceans and continents.

11. 2. Day breeze (land breeze) and night breeze (sea
breeze)
During day time, in hot sunshine, the land heats up
more quickly than the sea. Warm air rises above the
land, as it is displaced by cooler air moving in from the
sea. This is called day breeze.

12. At night the sea heats up. The sea stays warmer than
the land. Which cools down quickly, warmer air now
rises above the sea, as it is displaced by cooler air
moving out from the land. This process is called night
breeze.

13. 3. Hot water system
Cold water in the storage tank sinks down to the boiler,
where it is heated. The heated water in the boiler rises
to the top of the storage tank. In this way, a supply of
hot water collects in the storage tank from the top
down. The storage tank is insulated to reduce thermal
energy losses by conduction and convection. The
header tank provides the pressure to push the water
out of the taps.

14. 4. Refrigerator
Cold air sinks below the freezer compartment. This
sets up a circulating current of air which cools all the
food in the refrigerator.

15. 5. Air conditioner
Cold air sinks below the air conditioner and hot air at
the bottom of the room rises up. This sets up a
circulating current of air which cools all air in the
room.

16. 6. Room heating
Warm air rising above a convector heater or radiator
carries thermal energy all around the room-through
unfortunately; the coolest air is around your feet.

17. RADIATION
Radiation is the process by which heat is transmitted
from a hot object to another in the form of
electromagnetic waves (infra red).
This process does not require any medium.
It can take place in a vacuum.
Different objects give out different amounts of radiation,
depending on their temperature and their surface.
EMITTERS AND ABSORBERS
Some surface are better at emitting (sending out)
thermal radiation than others.
Good emitters of thermal radiation are also good
absorbers.
Black colour is good absorber and also good emitter of
thermal radiation.
White and silver colour are bad absorber and emitter of

18. COMPARING ABSORBERS
Put water two cans, one is painted with black colour
and another is painted with silver colour. Cover the
both cans and put thermometer to each cans and kept
both cans into direct sunlight for sometime.

19. It is found that the temperature of black colour can
higher than silver colour can.
This means black colour is good absorber of heat.

20. COMPARING EMITTERS
Put hot water into two cans, cover both the cans and
put thermometer into each can. Keep both cans
where there were no sunlight.
It is found that the reading of the thermometer in the
black can falls more quickly that silver can.
This means black colour is good emitter of thermal
radiation.

21. REDUCING HEAT LOST FROM HOMES
Energy tends to escape from a hot object, spreading to
its cooler surroundings by conduction, convection
and radiation. This can be a great problem. We may
use a lot of energy (and money) to heat our homes
during cold weather, and the energy simply escapes.
A well insulated house can avoid a lot of energy
wastage during cold weather. The insulation can also
help to prevent the house from becoming
uncomfortably hot during warm weather.