Class 7, Chapter 4- Heat, Lesson- 3

1. TRANSFER OF HEAT: CONDUCTION &
CONVECTION
Suman Kumar Krishna
Integrated B.Sc. B.Ed. (Medical)

2. • Heat flows from a body at a higher temperature to
a body at a lower temperature. This is called
transfer of heat. Heat is transferred in three
different ways.
They are :-
i) Conduction
ii) Convection
iii) Radiation
TRANSFER OF HEAT

3. Conduction
• Conduction is the transfer of heat from a
hotter part to a colder part of an object due
to the collision of its particles without actual
movement of the particles from their
position.

4. CONDUCTORS AND
INSULATORS
• Conductors :- Conductors are
materials which allow heat to
pass through them easily. E.g. :-
iron, aluminum, copper etc.
• Insulators :- Insulators are
materials which do not allow
heat to pass through them
easily. E.g. :- wood, plastic,
glass, rubber, air, water etc.

5. Just think: Will heat be transferred if temperature
of two objects are the same.

6. Convection
• The transfer of heat in liquids and gases is called Convection.
• The molecules of the liquid or gases that are near the source of the heat get
heated first. They become lighter due to the heat and move upwards.
• The colder particles being heavier take the place and this process continues
until the whole liquid or the gas gets heated.
• That is why the area above the flame of a candle always feels hot but the
area on the sides of the candle does not.

7. • Air is a very poor conductor of
heat, Air transfers heat from its
hotter parts to the colder parts
by the process of convection.
Convection in Air

8. • Water is a poor conductor of
heat. So, due to this reason, it
cannot transfer heat by
conduction but it transfers heat
by the process of convection.
Convection in Water

9. • What would happen if there is no
conduction of heat?
• What would happen if all object
around us become good conductor of
heat?
• What things that you see in your
surrounding which is related to
convection of heat?

10. Choose the Correct Option:
• Transfer of heat happens: -
a. hot to cold
b. cold to hot
c. hot to hot
d. cold to cold

11. State True or False:
• The materials which allow heat to pass through them
easily are conductors of heat. [True/ False].
• The water and air are poor conductors of heat.
[True/ False].

12. So, today we have learnt about ‘Transfer of heat: Conduction
& Convection’ and now let’s summarize today’s class:
Define the term Conduction of heat and Convection of
heat.
Tell one example of conduction of heat and one of
convection of heat.
Name two types of heat transfer.
State a difference between conductor of heat and
insulator of heat.

13. Homework
Take a sheet of paper. Draw a spiral on it
as shown in the Fig. Cut out the paper
along the line. Suspend the paper as
shown in Fig. 4.14 above a lighted
candle. Observe what happens. Think of
an explanation