1. 1.2 Transfer Processes
Conduction
Convection
Radiation
Introduction

2. Conduction Heat conduction solids fluids vacuum insulators conductors
molecular collisions
electronic motion

3. Energy transferred by conduction
Many cooking utensils are made of metal with plastic handles. Do you know why?
Conduction is a process in which heat flows through a
from places of temperature to places of
temperature.
Conduction and cooking
How does conduction take place?
Conduction along metal rods
Suggest three ways to increase the conduction rate in the above case.
Concept maps

4. Conduction in solids Conduction in solids
Experiments
Conduction in solids
polystyrene silver glass brick water wood aluminium
Arrange the above solid materials in descending order of conductivity (i.e. ).
are better conductors of heat than , or to say, are better insulators of heat than .
Concept maps

5. Does water conduct heat well?
Conduction in fluids
Experiments
Conduction in fluids
Does water conduct heat well?
In the figure shown, the ice are fixed at the bottom by wire gauze, and the water is heated at the top.
Observation:
Implication:
water
wire gauze
ice
Water is conductor of heat.
Concept maps

6. Does air conduct heat well?
In the figure shown, two thermometers are fixed on the cardboard tube containing air.
Observation:
Implication:
thermometer
cardboard tube
heater
Air is conductor of heat.
Applications
Since air is heat insulator, the following can keep warmth by in:
1. cotton jackets
2. polar bears
3. birds
Concept maps

7. Conduction and molecular motion
When a solid is heated at one end, why can heat be transferred to the other end by conduction?
Bunsen burner
Upon heating, molecules near the Bunsen burner move more and The
force in turn set the neighboring molecules also vibrate
The process continue and ( ) energy is transferred along the body as a result of molecular .
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8. Why do solids conduct heat better ? Why do metals conduct heat better?
Liquids and gases are conductors of heat than solids because , and so molecular collisions do not occur as as those in solids for fast energy transfer.
Why do metals conduct heat better?
Metals possesses which can carry energy directly from the hot end to the cold end. Therefore, most metals are conductors of heat.
Discuss why copper is so conducting compared to other metals.
Concept maps

9. CE – 2005 – 8 Cynthia places a carpet on a tile floor.
After a while, she stands in bare feet
with one foot on the tile floor and the
other on the carpet as shown above.
She feels that the tile floor is colder
than the carpet. Which of the following best explains this phenomenon?
A. The tile is a better insulator of heat than the carpet.
B. The tile is at a lower temperature than the carpet.
C. The specific heat capacity of the tile is smaller than that of the carpet.
D. Energy transfers from Cynthia’s foot to the tile at a greater rate than that to the carpet.
carpet
tile floor
Concept maps

10. Convection Heat convection solids vacuum fluids rising of hot fluids
falling of cold fluids
convection current

11. General meaning of convection
Air-conditioners are usually installed high in a room. Do you know why?
Convection is the process in which heat is transferred by the movement of hot fluid (liquid / gas) due to a temperature difference along a direction.
Experiments
Convection in water
Experiments
Convection in air
Convection occurs only in , not in nor
Concept maps

12. Convection current Convection current
2. Colder fluid comes down from above to the warm fluid, forming a convection current flowing in the fluid.
1. When a fluid is heated from below, that part of the fluid and becomes That part of fluid therefore
is transferred by convection.
Concept maps

13. Drawing convection current
Sketch the convection current formed in the following cases.
(I) (II)
 D  A
 C  B
Compare points A and B in Figure (II). Which point has a higher
(i) temperature
(ii) air density?
(c) Compare points C and D in Figure (II). Which point has a higher
Correct diagrams?
Concept maps

14. Other related phenomena
Formation of sea and land breezes
Day times
Night times
During day times, lands have
temperature than sea (why?). Warmer air over the rises while cooler air over the flows in to take its place forming the breeze.
During the night, lands have temperature than sea (why?). Warmer air over the while cooler air over the flows in to take its place forming the breeze.
The running lantern
Concept maps

15. electromagnetic radiation
Heat
radiation
Solids
fluids
vacuum
infra-red radiation
electromagnetic radiation
green house
effect
dull black surface
shiny white surface

16. Identity of heat radiation
When we put our hand beside a lamp, our hand feel warm quickly. Is heat transferred from the lamp to our hand by
(i) conduction?
(ii) convection?
Radiation is the process in which heat is transferred from one place to another by means of electromagnetic waves called .
Heat radiation is an invisible form of which can travel in with a high speed of m s-1.
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17. Factors affecting rate of emission
Emission of radiation
All objects than the surrounding emit heat radiation in direction. Hotter objects emit heat radiation in a given time.
StarX
Factors affecting rate of emission
The rate of emission of radiation depends on the following factors of the radiators:
1. Temperature,
2. Surface area,
3. Nature of surface.
Concept maps

18. Good and poor heat radiators
Dull black surfaces are heat radiators than shiny white surfaces.
Experiments
Emission and absorption of heat
The following conical flasks contain same amount of hot water at the same temperature. Which one records a higher temperature after some time?
A: Dull black surface
B: Shiny white surface
Hot water
Give examples of good and poor heat radiators in daily lives.
Concept maps

19. Absorption of radiation
Radiation through a medium
When radiation falls onto a substance, the energy of the incoming radiation would change to : 1. 2. 3.
(1)
(2)
(3)
Radiation falls on different surfaces
Shinny surface
Dark surface
Transparent surface
Which surface is the hottest after the lamp has been turned on for a few minute?
Concept maps

20. Good and poor heat absorbers
Dull black surfaces are heat absorber than shiny white surfaces.
Experiments
Emission and absorption of heat
Which air-filled conical flask is hotter after the lamp has been turned on for a few minute?
Lamp
A: Dull black surface
B: Shiny white surface
Dull black / shiny white surface becomes hotter upon more efficient absorption / emission of radiation. Heat is then transferred from the hot surface to the air inside by conduction / convection / radiation.
Concept maps

21. The thermal flasks
A thermal flask (or thermos) can keep drinks hot or cold by reducing heat exchange with the surrounding through conduction, convection and radiation.
support to reduce heat loss by .
glass wall to reduce heat loss by .
to reduce heat loss by
to reduce heat loss by
Experiments
The thermal flasks
Concept maps

22. The thermal cookers
A thermal cookers can keep foods hot or cold by reducing heat exchange with the surrounding through conduction, convection and radiation.
1.Inner and outer to reduce heat loss by
steel wall to reduce heat loss by .
3.Outer to reduce heat loss by
3.An film between inner and outer pots acts as
Concept maps

23. The greenhouse effect
A green house has a glass roof and glass walls constructed to keep plants warm.
3. The low energy radiations can no longer pass through the glass but is repeatedly inside the house.
The sun emits radiations that are energetic enough to get enter the glass.
4. Radiations are thus inside the house and warm up the plants inside.
2. Radiations after entering the glass become
Experiments
The greenhouse effect
Concept maps

24. CE – 2005 – 7
A hot potato is wrapped by shiny aluminium foil. By what means can the foil help reducing the rate of energy lost from the potato to the surrounding?
(1) conduction (2) convection (3) radiation
A. (2) only B. (3) only C. (1) and (2) only D. (1) and (3) only
A space shuttle is covered by `heat shields’ over its body so as to protect the interior from getting too hot while entering the atmosphere of the Earth. Which of the following thermal properties is/are desirable for the material of the `heat shields’?
(1) It should be a good conductor of heat.
(2) It should have a very high melting point.
(3) It should have high specific heat capacity.
A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only
CE – 2005 – 7
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25. CE – 2006 – 9
The figure shows a vacuum flask with two glass walls. Which of the following statements are correct?
(1) The surface P and Q are painted silvery to reduce heat loss.
(2) The cork stopper reduces heat loss by conduction and convection.
(3) The vacuum between the double glass walls reduces heat loss by radiation.
A. (1) and (2) only B. (1) and (3) only
C. (2) and (3) only D. (1), (2) and (3)
surface P
surface Q
cork stopper
hot liquid
glass walls
vacuum
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26. CE – 2007 – 9 The diagram below shows the structure of a cake.
The ice-cream inside the cake does not melt when it is baked in an oven. Which of the following are possible reasons for this phenomenon?
(1) The whipped egg white is a poor conductor of heat.
(2) The whipped egg white is a good radiator of heat.
(3) The sponge cake is a poor conductor of heat.
A. (1) and (2) only B. (1) and (3) only
C. (2) and (3) only D. (1), (2) and (3)
Concept maps