This document discusses different modes of heat transfer - conduction, convection, and radiation. It explains that conduction involves direct contact between objects, convection involves the transfer of heat by liquid and gas particles, and provides examples of each. It also differentiates between conductors and insulators, and describes the phenomena of sea breezes and land breezes that occur due to differences in how land and sea heat and cool.

1. Heat
Part-3
FOR CLASS VII
By- Vivek Singh
ABPS JAGDISHPUR

2. Key points in this power point
• Transfer of heat
• Conduction
• Conductors and insulators
• Convection
• Convection in air
• Sea breeze and land breeze

3. TRANSFER OF HEAT
• 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

4. Conduction
• Conduction is the process by which heat is
transferred in solids from the hotter end to the
colder end.

5. Conduction
• Transfer of heat through direct contact.
• Occurs anytime objects at different temperatures
are touching each other.
• As long as the objects are in contact, transfer of
heat will continue until the temperature of the
objects is the same.

6. • Example: If you leave a metal spoon in a pan of
soup that you are heating on the stove, it may burn
your fingers.
• The spoon is in direct contact with the hot soup
and heat is transferred to the spoon.

7. Activity :-
• Take an iron or aluminium rod or strip.
• Fix a few wax pieces on at equal distances.
• Clamp the rod to a stand.
• Heat the other end of the rod.
• The wax pieces begin to melt and fall down from
the heated end.

8. This shows that heat is transferred from the hotter
end to the colder end by conduction.

9. Conductors and insulators
• Conductors :- Conductors are materials which
allow heat to pass through them easily.
• E.g. :- iron, aluminium, 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.

10. Convection
• Convection is the process by which heat is
transferred in liquids and gases from the hotter
part to the colder part.

11. Convection
• The transfer of energy in a liquid or gas.
• When part of a gas or liquid is heated, the
particles it is made up of move faster and spread
out more.
• The moving particles bump into other particles,
causing them to move faster and spread out
more.

12. Activity :-
• Take some water in a round bottom flask.
• Keep it on a tripod stand.
• Put a crystal of potassium permanganate in it.
• Heat it with a burner.
• The water at the bottom becomes hot and rises
up and cold water from the top moves down.

13. • This water becomes hot and rises
up and cold water from the top
moves down and the process
continues till all the water gets
heated.
• This shows that heat is
transferred by convection.
Process of convection

14. Convection in air
• The air near the heat source gets heated and
rise up.
• The air from the sides move in to take its place.
In this way the air gets heated.

15. • If you keep one hand above a flame and one hand
on the side of the flame, the hand at the top
feels hot because the air above is heated by
convection.
• The hand at the side does not feel as hot
because there is no convection.

16. SEA BREEZE AND LAND BREEZE
Sea breeze :-
• During the day the land gets heated faster than
the sea. So the air above the land gets heated
becomes hotter and rises up and cool air from the
sea moves towards the land. This is called sea
breeze.

17. SEA BREEZE…
Air moves from the sea during the day.

18. Land breeze :-
During the night sea cools down slowly than the
land. So the hot air above the sea rises up and
cool air from the land moves towards the sea.
This called land breeze.

19. LAND BREEZE….
air moves from the land at night

20. Assignment
• Make note of all slides in your notebook.
• Write 5 examples of conductors and insulators.
• Write difference between conduction and
convection.
• Write difference between see breeze and land
breeze.

21. THANK YOU