Class 7, Chapter 4- Heat, Lesson- 4

1. TRANSFER OF HEAT: LAND/ SEA BREEZE
AND RADIATION
Suman Kumar Krishna
Integrated B.Sc. B.Ed. (Medical)

2. • The wind blowing from the land towards
the sea is called the land breeze.
• During the night time, the land in the
coastal areas gets cool down faster than
the sea. The air above the sea is hotter
than the air above the land.
• Therefore the air above the sea rises and
the air from the land being cool flows
towards the sea. This results in the land
breeze.
Land Breeze

3. Sea Breeze
• The wind blowing from the sea
towards the land is called Sea
Breeze.
•
• During the daytime, the land in
the coastal area gets heated due
to the sun's radiation.
• The sea also gets heated,
however it takes more time to
get heated up than the land.

4. • Hence the air above the land
gets heated faster than the air
above the sea.
• The hot air from the land rises
above as it is lighter and the
cool air from the sea being
heavier takes its place. This
results in the sea breeze.

5. Just think: how does the heat come to us from
sun and which type of transfer of heat is involved
in it and why?.

6. Radiation
• The mode of transfer of heat through which heat energy from a
hot body to a cold body by means of heat rays without any
material medium between them is known as radiation, e.g. the
sun’s heat reaches the earth by the process of radiation.
• The sun is very far away from the earth, and there is mainly an
empty space (vacuum) between the sun and the earth even, then
the heat from the sun reaches the earth.
• This is due to the fact that the sun being extremely hot, emits
invisible heat radiation (or infrared rays) in all directions.

7. • These radiations travel through
the vacuum between the sun
and the earth at a very high
speed and ultimately, reach us
on the earth.
• Therefore, we can say that the
transfer of heat from a hot object
to a cold object by the process
of radiation does not require any
medium.

8. • Woollen clothes are obtained from
animal fibers. Woollen clothes are
generally dark in color and are worn in
the winter season as they protect us
from the cold environment.
• Cotton clothes are obtained from the
plant fibers. The cotton clothes are
generally light in color and are worn in
summer season so that we can feel
cool.
CLOTHES IN WINTERS
AND SUMMERS

9. • In the winters, we use
woolen clothes. Wool is a
poor conductor of heat.
Moreover, there is air
trapped in between the
wool fibers.
• This air prevents the flow of
heat from our body to the
cold surroundings. So, we
feel warm.
How woolen clothes keep
us warm in winter?

10. • What would happen if Air around us
doesn’t move?
• What would happen if sun suddenly
disappears or there is no sun?
• What would happen if you are made
to wear woolen clothes in summer and
cotton clothes in winter?

11. Choose the Correct Option:
• Breeze that blows from the massive water
bodies are termed as: -
a. Sea Breeze
b. Land Breeze
c. Desert Breeze
d. Air Breeze

12. State True or False:
• The transfer of heat by radiation does not require any
medium. [True/ False].
• From the sun heat comes to us by another process
known as radiation. [True/ False].

13. So, today we have learnt about ‘Transfer of heat: Land/ Sea
Breeze and Radiation’ and now let’s summarize today’s class:
Define the term convection of heat and heat radiation.
Tell one example of convection of heat and one of heat
radiation.
Tell one difference between sea breeze and land breeze.
Explain why do we use light color umbrella in summer.

14. Homework
Wrap a thin paper strip tightly around an iron rod. Try to burn
the paper with candle while rotating the iron rod continuously.
Does it burn? Explain your observation.