Heat is a form of energy that transfers from one point to another due to temperature differences. Heat can cause expansion of substances and increase their temperature. There are several ways heat transfers, including conduction, convection, and radiation. Thermometers use liquids like mercury or alcohol to measure temperature changes based on thermal expansion principles.

1. HEAT ENERGY
Heat is a form of energy
that travels from one point
of a medium to the other
due to temperature
differences.
What is heat energy?

2. HEAT ENERGY
• Heat can also said to be the total
amount of energy in a substance.
• This total energy is made up of both
kinetic and potential energies of the
molecules of the substance.
• The S.l. unit of heat is the Joules(J)
• Heat can be converted into other forms
of energy such as electrical and light
energies.``

3. HEAT ENERGY
1.The Sun (natural source)
2.Burning of petroleum and its products
3.Biomass
4.Hydroelectric power
5.Chemical reactions
6.Nuclear reactions
7.Geothermal energy (heat energy from
the core of the earth)
Sources of Heat

4. HEAT ENERGY
1.Heat causes increase in temperature
of substances
2. Heat causes change of state of matter
of substance
3. Activates chemical reactions of
matter.
4. Causes increase in volume of
substances (expansion)
Effects of Heat on
substances

5. HEAT ENERGY
Heat cannot be measured directly but its effect on
a substance can be detected.
Changes in heat can usually be detected as
changes in temperature.
1. When heat is added to a substance, kinetic
energy of the molecules increases and
temperature of the substance also increases.
2. When heat is removed from a substance,
kinetic energy of the molecules decreases and
temperature of the substance also decreases.
Relationship between Heat and
Temperature

6. HEAT ENERGY
Temperature can be
defined as the degree of
hotness or coldness of a
body.
What is temperature?

7. HEAT ENERGY
• Temperature can measured in
1.degree Celsius (°C.)
2.degree Fahrenheit (°F.)
3.Kelvin (K)
• The S.I unit for measuring
temperature is Kelvin(K)
• The instrument for measuring
temperature is the thermometer.

8. HEAT ENERGY
1. It causes a rise in
temperature of bodies
1. It is the degree of hotness
or coldness of a body
2. It is a form of energy
2. It is not a form of
energy
3. It is measured in
Joules
3. It can be measured in
kelvin or degree Celsius
4. It can be transferred
from one point to
another
4. It cannot be transferred
from one point to another
Differences between Heat and Temperature

9. HEAT ENERGY
Temperature Scales
The temperature scales used in
most scientific work is the
1. Celsius scale which is also known
as the centigrade scale and the
2. thermodynamic scale which is
also known as the kelvin scale or
the absolute scale.

10. HEAT ENERGY
Upper fixed point(UFP) and
lower fixed point(LFP)
The upper fixed point is the
temperature of steam from pure
water boiling under normal
atmospheric pressure.
The lower fixed point is the melting
point of pure ice at normal pressure.

11. HEAT ENERGY
UFP and LFP
• On the Celsius scale the upper
fixed point is 100 °C and the
lower fixed point is 0 °C.
• On the kelvin scale the upper
fixed point is 373 K and the
lower fixed point is 273 K.

12. HEAT ENERGY
Fundamental interval
The interval between the upper
and lower fixed points is called
the fundamental interval.
This interval is divided into 100
equal parts and each part defines
one degree Celsius or one kelvin.

13. HEAT ENERGY

14. HEAT ENERGY
The fundamental interval on the
Celsius and kelvin scales is the
same.
Conversion from one scale to the
other is simply done by adding or
subtracting 273 as appropriate.
Conversion of temperature scales

15. HEAT ENERGY
Conversion of temperature scales

16. HEAT ENERGY
Conversion of temperature scales
Where T is temperature in Degree Celsius

17. HEAT ENERGY
Conversion of temperature scales
Freezing point of alcohol is -115C
Freezing point of mercury is -39C
Boiling point of mercury is 357 °C
Boiling point of alcohol is 78 °C

18. HEAT ENERGY
1. For drying objects like our clothes, fish,
cocoa and corn.
2. For warming our homes
3. For cooking, baking and ironing
4. For sterilising medical instruments in
hospitals
5. For burning fossil fuels in engines
6. At the workplace heat is used for
melting metals
Uses of heat energy

19. HEAT ENERGY
1. Liquid-in-glass thermometer e.g. clinical
and laboratory thermometers
2. Bimetallic thermometers
3. Gas thermometers
4. Pyrometers used in very hot places e.g.
pottery industry,hospitals
5. Thermocouples
6. Digital and electronic thermometers
Types of thermometers

20. HEAT ENERGY
Types of thermometers
Bimetallic thermometers: it is applied in
making the thermostat in electric gadgets.
Gas thermometers: used to measure the
temperature of molten iron and aluminum.
Pyrometers: used in the pottery industry to
read the temperature in a kiln.

21. HEAT ENERGY
Liquid-in-glass Thermometers
Liquid-in-glass
thermometer refers to a
thermometer which
contains thermally sensitive
element is a liquid (mercury
or alcohol) contained in a
graduated glass envelope.

22. HEAT ENERGY
Types of liquid-in-glass thermometer
1. Clinical thermometer :used to measure
temperature of the human body.
2. Laboratory thermometer: used to measure
temperature changes of substances with high
degree of precision.
3. Six maximum and minimum thermometers:
used to determine the maximum temperature
during the day and the minimum temperature
during the night.

23. HEAT ENERGY
Uses of parts of thermometer
The liquid-in-glass thermometer consists of a liquid which
flows through a fine capillary tube in a thick glass wall. It
has
1. A bulb that serve as the reservoir of the liquid.
2. A stem with fine uniform capillary glass tubing
through which the liquid rises when the temperature
increases and falls when the temperature decreases.
3. Calibration (markings) on the stem to read the
temperature.
4. Kink prevents the mercury from falling back into the
bulb.

24. HEAT ENERGY
Thermometric liquid
A thermometric liquid is the liquid
used in liquid-in-glass thermometers.
Liquids used are mostly alcohol and
mercury.
This is because of special qualities they
have that other liquids like water do
not have.

25. HEAT ENERGY
Thermometric liquid
A thermometric liquid is the liquid
used in liquid-in-glass thermometers.
Liquids used are mostly alcohol and
mercury.
This is because of special qualities they
have that other liquids like water do
not have.

26. HEAT ENERGY
Qualities of a good thermometric liquid
1. The temperature range within which it
remains a liquid is large.
2. It expands regularly and evenly with a
rise in temperature.
3. It does not cling to the wall of the glass
tubing i.e. it should not wet glass.
4. It should be easy to see i.e. it should be
coloured.

27. HEAT ENERGY
Why water is not used in liquid-in-gas thermometers
1. It expands irregularly at certain
temperatures.
2. It wets glass by clinging to it.
3. It vaporizes and later condenses in
the glass tubing.
4. The temperature range within which
it freezes and boils is very small

28. HEAT ENERGY
Advantages of alcohol over mercury as a thermometric liquid.
1. Alcohol has a lower freezing point
(-114 °C) than mercury (-39 °C). This
explains why they are used to
measure temperature in very cold
regions.
2. Alcohol has a high expansivity, about
six times than that of mercury

29. HEAT ENERGY
Why mercury is preferred in most liquid-in-
glass thermometer over alcohol
1. It has a boiling point of 357°C and a freezing point of -
39°C. This gives a wide temperature range
2. It expands and contracts regularly with an increase or
decrease in temperature.
3. It does not cling to the wall of glass tubing (it does not
wet glass).
4. It is opaque and therefore can be seen in the glass
easily.
5. Mercury is not as volatile as alcohol.
6. Mercury has a high specific heat capacity.

30. HEAT ENERGY
Clinical thermometers
Clinical thermometers are liquid-in-glass thermometers
that are used in clinics and hospitals to measure human
body temperature. It has a temperature range between
34°C and 43°C. The average human body temperature is
37°C

31. HEAT ENERGY
Features of clinical thermometer
1. It has a temperature range between 35°C
and 43°C.
2. The fine bore of the tube makes the
thermometer very sensitive to temperature
changes.
3. Narrow constriction or kink: prevents the
mercury from falling back into the bulb on
its own

32. HEAT ENERGY
How the clinical thermometer works
When the thermometer is put under a person's tongue or
armpit and left for some times, the mercury thread
expands along the tube until the body temperature is
reached.
When the thermometer is removed, the mercury column
does not contract into the bulb, but remains at the same
level.
It breaks at the kink and the temperature is recorded. It is
shaken vigorously to force the mercury into the bulb. The
thermometer is then sterilized in an antiseptic solution
before reuse.

33. HEAT ENERGY
Guidelines for using a liquid-in-glass thermometer
1. The substance is stirred so that the same temperature is
maintained throughout the entire substance.
2. The thermometer is placed in the substance to be
measured for a short period of time before
measurements are taken to allow the liquid in the
thermometer to expand or contract to the correct
temperature.
3. The bulb does not touch the bottom or the wall of the
container.
4. You hold the opposite end of the thermometer to that
which is in the substance.
5. You read the scale at the correct point of the meniscus.

34. HEAT ENERGY
Why boiling water is not used in sterilizing
clinical thermometer
This is because clinical thermometers are made in such a
way that they can measure body temperatures up to 43°C
(maximum temperature) and since water boils at 100°C,
using boiling water for sterilization may cause the glass of
the thermometer to crack because of excessive expansion.
Importance of sterilizing clinical
thermometers
This is to help prevent the spread of germs i.e.
microorganisms that cause disease from one patient to
another

35. HEAT ENERGY
Advantages of liquid-in-glass thermometers
1. They are very portable and so can easily be
carried from one place to another.
2. They are less expensive than other types of
thermometer.
3. Their operation is very simple to
understand.
4. The liquid used in them (mercury or
alcohol) can be easily be obtained.

36. HEAT ENERGY
EXPANSION AND CONTRACTION COMPARED
Thermal expansion refers to increase in size,
length and volume of objects when they are
heated.
Whiles
Thermal contraction refers to the decrease in
size, length and volume of objects when they
lose heat.

37. HEAT ENERGY
Explanation of expansion and contraction of objects
When a substance is heated, there is an increase in
temperature and molecules of the substance vibrate
faster and move faster in the body i.e. kinetic energy
of the molecules increases. This increase in kinetic
energy and the increase in distance between
molecules in the substance results in the expansion of
the substance.
As the substance cools i.e. taking away heat, there is
a decrease in temperature and kinetic energy of the
molecules reduces and the average distance between
the molecules become less hence, the contraction.

38. HEAT ENERGY
An experiment to demonstrate that heating causes
expansion in metals(solids)
Materials /apparatus
The apparatus consist of a metal ball and a ring which is
constructed in such a way that at room temperature the
ball passes through the ring easily.

39. HEAT ENERGY
An experiment to demonstrate that heating causes
expansion in metals(continued)
Method:
The metal ball is heated in the Bunsen flame and then
placed in the ring
Observation
The ball was unable to pass through the ring after it has
been heated but upon cooling it did.
Conclusion:
Thermal expansion occurred in the ball when it was heated
and this explains why it was unable to pass through the ring
until it was cooled.

40. HEAT ENERGY
An experiment to demonstrate that heating causes
expansion in liquids
Apparatus/materials: Round-bottom flask, retort stand and clamp,
glass tube, rubber bung, Bunsen burner, water which has been dyed
Method: Apparatus are arranged as shown below.

41. HEAT ENERGY
An experiment to demonstrate that heating causes
expansion in liquids
Observation:
The level of the liquid first falls (due to
expansion of the flask) but rises gradually (due
to expansion of the liquid).
On cooling, the liquid returns to its original
level.
Conclusion
Liquids expand on heating and contracts upon
cooling.

42. HEAT ENERGY
An experiment to demonstrate that heating causes
expansion in liquids
NOTE: Initial fall in level of liquid is caused by
expansion of the flask when heated before
heat is conducted through it into the liquid for
it also to expand.

43. HEAT ENERGY
Disadvantages of Expansion and contraction in
Everyday life
1. Sagging of overhead electric cables
2. Cracking of thick glass bottle or glass
cup
3. Damage to bridges
4. The crackling noise heard from the
metal roofs on hot afternoons
5. The bulging of railway tracks
6. Damage to terrazzo work:

44. HEAT ENERGY
Disadvantages of Expansion and contraction in
Everyday life
1. Sagging of overhead electric cables
2. Cracking of thick glass bottle or glass
cup
3. Damage to bridges
4. The crackling noise heard from the
metal roofs on hot afternoons
5. The bulging of railway tracks
6. Damage to terrazzo work:

45. HEAT ENERGY
Application of Expansion and contraction in
Everyday life
1. Expansion gaps are left between metal parts in bridges
to allow for expansion when heated by the sun.
2. Metal roofing sheets have their ends placed one on top
of the other to allow for expansion. The cracking noise
heard from metal roofs during the afternoon is due to
the expansion of the roofing sheets.
3. Buildings have expansion gaps between the concrete
blocks.
4. Gaps are left between blocks in terrazzo works.
5. Gaps are left in railway lines to allow for expansion so
that the rails do not bend.

46. HEAT ENERGY
Other applications of thermal expansion and contraction in machines
1. Remove very tight metal lids of bowls and
bottles
2. Fit metal wheels on axles of trains
3. Construct thermostats in household
electrical appliances
4. Construct bimetallic thermometers
5. Rivet steel plates together in ship building
and in the construction of boilers

47. HEAT ENERGY
Application of Expansion
1. Steel rods are placed in concrete beams to
strengthen them because they both expand
equally.
2. Thermometers are constructed on the
bases of expansion and contraction of
liquids.
3. Bimetallic strips for construction of a
temperature controlling device called
thermostats which bend to cut off or
connect the electricity supply temporarily.

48. HEAT ENERGY
Bimetallic Strip
The bimetallic strip consists of strips of two
different metals, such as brass and iron of the
same length, fastened together.
It is straight when at room temperature.

49. HEAT ENERGY
Bimetallic Strip
When it is heated the strip curves. The metal
with the greater expansion being on the
outside of the curve. A temperature increase
causes the brass to expand more than the
iron

50. HEAT ENERGY
Bimetallic Strip
On the other hand, when the same
bimetallic strip is cooled below room
temperature it bends so that the brass is
on the inside of the curve

51. HEAT ENERGY
Uses of bimetallic strip
1. Thermostats as in electric irons, gas
cookers, refrigerators, electric kettles,
rice cookers and air conditioners.
2. Oven thermometers as in bimetallic
thermometers.
3. Electric flasher unit of motor cars for
directing traffic.

52. HEAT ENERGY
Using the thermostat
The thermostat is a temperature or
heat controlling device for maintaining
a study temperature.
It is fixed mostly in electrical heating
appliances such as electric iron, deep
freezers, and electric cooker.

53. HEAT ENERGY
Operation of thermostat in electric Iron:
When these electrical appliances get over heated,
the bimetallic strips in them expand and bend,
thus cutting off current to control the temperature
of the appliances.

54. HEAT ENERGY
Transfer of Heat
Heat naturally transfers from a body with a
higher temperature to a body with a lower
temperature. There are three main
mechanisms by which heat is transferred from
one body to another:
1. Conduction.
2. Convection.
3. Radiation.

55. HEAT ENERGY
Conduction
Conduction is the transfer of heat
through a material from a place of higher
temperature to a place of lower
temperature without the molecules of
the material moving as a whole.

56. HEAT ENERGY
Conduction
Conduction is the direct
transfer of heat energy from
one substance to another.
OR
It is the transfer of heat in
solids that are in contact.

57. HEAT ENERGY
Conduction
Conduction is the direct transfer of heat energy from one
substance to another.
It is the transfer of heat in solids that are in contact.
The conduction of heat energy always occurs from a region
of higher temperature to a region of lower temperature
until temperatures in both regions reach a state of
equilibrium.
For example, when a cooking pot is placed on the solid
surface of a hot stove, the pot comes in direct contact with
the stove element and heat is transferred to the pot by
means of the movement of molecules (kinetic energy).

58. HEAT ENERGY
Good Conductors and Bad Conductors of heat energy
Materials that conduct heat are called
conductors.
Good conductors of heat
A good conductor of heat is any substance which
conducts heat easily and rapidly.
Good conductors of heat are usually metals and
hence have free electrons. Examples are copper,
aluminium, iron, brass, tin, lead.
Good conductors of heat are often times also
good conductors of electricity

59. HEAT ENERGY
Bad conductors of heat
Bad conductors of heat
A bad conductor of heat is any substance which does
not conduct heat easily and rapidly.
Examples are cork, wood, paper, concrete, felt,
sawdust, plastics, leather, water and porcelain.
Insulators are used in winter clothing, roofing insulation
and in lagging(wrappings) for ovens, refrigerators and
pipes.
These substances are usually non-metallic and have no
free electrons.Bad conductors of heat are also called
insulators and hence they are used as such.

60. HEAT ENERGY
Factors that affects conduction in solids
For a solid that conducts heat, the rate of
conduction depends on
1. the nature of the solid.
2. the thickness of the solid.
3. the difference in temperature between two
points on the solid (temperature gradient).

61. HEAT ENERGY
Uses of conductor and insulators
1. Metals like aluminium and silver are used in making cooking
utensils because
• they are good conductors of heat.
• they are relatively light.
• they resist corrosion/does not rust.
• they are not poisonous.
3. In the kitchen most cooking utensils have handles made of
insulators such as plastics, wood and porcelain so that one
can easily touch them and pick them up without being burnt
when on fire or when heated.
4. Insulators help to control temperature.
5. In cold areas people wear thick clothing and sweaters to
insulate their bodies against heat loses.

62. HEAT ENERGY
Experiment to show conduction of heat in solids
Materials needed
1. Metal rod
2. Drawing pins
3. Candle wax
4. Stop watch/clock
5. Bunsen burner

63. HEAT ENERGY
Experiment to show conduction of heat in solids
Procedure
Place or clamp the metal rod in a horizontal manner.
Attach pins at various intervals on the rod with the aid of the candle
wax.
Heat the rod at one end and start the stop watch at the same time.
Take note of the time each pin falls when candle wax melts.
Observation
After sometime, the candle wax will begin to melt and pins fall off.
Wax closest to source of heat melts in a shorter time, hence pins
closest to heat source fall first (pins fall in a specific manner)
Conclusion
Heat moved through solid rod from hottest end to coolest end.
Conduction has taken place as heat travelled from region of higher
temperature to one of lower temperature.

64. HEAT ENERGY
Experiment to show conduction of heat in solids(II)
Materials needed
1. Metal rod
2. Candle wax
3. Stop watch/clock
4. Bunsen burner
5. Retort stand and clamp

65. HEAT ENERGY
Experiment to show conduction of heat in solids
Method
One end of a metal rod is dipped in some molten candle wax and the
candle wax allowed to cool and solidify. The rod is clamped in the
middle.
The end of the rod which was not covered with candle wax is put in a
hot flam
Observation
The heat of the flame causes the candle wax along the metal rod to
melt.
metal rod by the process of conduction.
Conclusion
Heat moved through solid rod from hottest end to coolest end.
Conduction has taken place as heat travelled from region of higher
temperature to one of lower temperature.

66. HEAT ENERGY
Convection
Convection is the transfer of heat from
one place to another by the movement of
the hot body carrying the heat itself due
to differences in temperature.
Convection usually takes place in liquids
and gases (fluids) but not in solids.

67. HEAT ENERGY
How does convection occur?
• When a liquid or gas (fluid) is heated the particles
gain kinetic energy.
• Particles therefore move (vibrate) more quickly and
push themselves further apart (the fluid expands).
• Density of fluid decreases since mass remains the
same.
• Warm fluid with lower density tries to move
upwards as it tries to float on top of cooler fluid with
higher density.
• Warm fluid rises and cool fluid falls to replace it until
all acquire same temperature.

68. HEAT ENERGY
How does convection occur?
If liquid in a vessel is heated,
• it expands
• density decreases
• and remains floating on the
denser liquid beneath.

69. HEAT ENERGY
An experiment to show convection currents in a
liquid e.g. water
Procedure(Method)
1. Fill a flask, beaker or a suitable
container with water or any
liquid.
2. With the help of a glass tube
place a crystal of potassium
permanganate (purple colour)
at one corner of the bottom of
the beaker.
3. Gently remove the glass tube.
4. Heat gently the beaker and its
content where the crystal is
located.

70. HEAT ENERGY
Observation
• It would be observed that there is an upward movements
of coloured (purple colour) water/liquid from the region
of the crystals to the top.
• Coloured stream reaches top and spreads out and then
after sometime circulates down the sides of the beaker.
• Heat is carried from one place to another in the
water/liquid by the movement of the water/ liquid itself.
Conclusion
• The upward movement of coloured liquid and its
replacement by uncoloured liquid is due to convection.
• The circulation of liquid is called convection current.
• Convection current has set up.
An experiment to show convection currents in a liquid e.g. water

71. HEAT ENERGY
1. Land and sea breezes
2. The formation of clouds
3. The functioning of the refrigerator
4. The floating of balloons
5. The domestic hot water system
6. The ventilation of rooms: A room is said to be
ventilated when the air inside is fresh and pure. When
windows are open at night warm air escape from the
hot room and cool air from the outside flows in and
replaces it
7. The cooling system of an engine
The process of allowing cool air to replace hot air in the
room is called ventilation
Practical applications of convection currents

72. HEAT ENERGY
Sea Breeze
When the sun shines, it heats up the sea and the land. The
land gets warm quickly than the sea. The air above the land
also warms up. The warm air rises to replace the cooler air
above the sea. This produces a convection current called the
sea breeze from the water towards the land. So breeze
blows towards the land to cool it.

73. HEAT ENERGY
Land Breeze
At night the temperature of the air over the land fells
quickly because the land loses its heat rapidly. This means
the sea becomes relatively warmer than the land. The warm
air over the sea then rises while cool air from the land blows
towards the sea. This process of warm air from the sea
replacing cool air from the land is land breeze

74. HEAT ENERGY
Radiation
Radiation
Unlike conduction and convection,
this mode of heat transfer does not
require a material medium (does not
involve movement of particles or
contact between substances).

75. HEAT ENERGY
Radiation
Radiation is the process of heat transfer which
occurs in vacuum (empty space)
OR
Radiation is the transfer of heat energy from
one place to another without any material
medium.
OR
Radiation is the transfer of heat energy from
one place to another by means of
electromagnetic radiation.

76. HEAT ENERGY
Demonstration of Radiation
When a hand lens is used to direct the sun’s
rays on a dry sheet of paper, it catches fire
and burns.
This is because the sun radiates heat energy.
When this energy is focused on the paper it
raises its temperature to a level where it
catches fire.
The energy from the sun travels through
space, which is a vacuum by radiation.

77. HEAT ENERGY
Good absorbers(emitters) and Bad
absorbers(reflectors)
Good absorbers of radiant heat energy
are also good radiators/emitters and
hence bad reflectors (dull black surfaces).
Bad absorbers are bad emitters/radiators
(bright shiny surfaces) and hence good
reflectors.

78. HEAT ENERGY
Objects that are hotter than their
surroundings radiate or give off heat.
Examples include
1. a heated box iron
2. heated oven
3. a hot coal pot
4. a heated electric iron
Objects that radiate heat lose their energy
and cool down.
Examples of Objects that radiate heat

79. HEAT ENERGY
Application of radiation
1.Electric room heaters
2.Shiny surfaces of teapots:
3.Base of a cooking utensil
4.Reflecting solar films
5.Petrol storage tanks
6.Solar cooker (and solar water heater)
7.Choice of clothes
8.Construction of thermos flask
9.Kettles are silver-coated to reduce the
amount of heat radiation given out while the
water is being heated.

80. HEAT ENERGY
Explanations of some applications
1. White or light coloured clothes are more comfortable to
wear on sunny days because they reflect heat rather than
absorb it.
2. Gas tanks are painted with silver paint to reduce the
amount of heat it absorbs. This ensures that gas
temperature and pressure do not get too high.
3. Kettles are silver-coated to reduce the amount of heat loss
by radiation while water is being heated.
4. Water reservoirs are painted with silver paint to reduce the
amount of heat absorbed. This is to reduce water loss by
evaporation.
5. The cooling fins of deep freezers are painted black to emit
as much heat by radiation as possible.

81. HEAT ENERGY
THERMOS FLASK
The thermos flask
is designed to keep
hot substances like
porridge; hot
water etc. hot and
cold substances
cold. Heat entering
or leaving the flask
is greatly reduced
because of the way
it is designed.
The Thermos or Vacuum Flask

82. HEAT ENERGY
Features or parts of a thermos flask
1.Consist of double-walled glass vessel
with a vacuum between the walls.
2.Both glass walls facing each other are
silvered on the vacuum side.
3.Has cork supports at the bottom.
4.Has plastic or cork stopper.
5.Enclosed in metal or plastic container.

83. HEAT ENERGY
How it works(Functions of parts)
1. The supports and the stopper prevent heat
lose or gain by conduction.
2. The vacuum within the double walls of the
flask also prevent heat lose or gain by
conduction and convection.
3. Radiation of heat from the flask is
prevented by the silver-coated inner
surfaces of the walls of the flask, which
reflect heat that would have passed out into
the flask.

84. HEAT ENERGY
Method(Procedure)
1.Two surfaces, one painted dull black and the other highly
polished are placed vertically a few centimetres apart.
2.At the back of each side of the two surfaces, a cork is
attached by means of candle wax.
3.A candle or Bunsen burner is lit and placed half way
between the two surfaces so that both surfaces receive
equal amount of heat energy.
4.The set up is left to stand for a few minutes.
Experiment to show that dark surfaces are good
absorbers of heat and shiny surfaces are poor
absorbers of heat

85. HEAT ENERGY
Experiment to show that dark surfaces are good absorbers of heat and
shiny surfaces are poor absorbers of heat

86. HEAT ENERGY
Observation
The wax behind the dull black surface begins to melt
and the cork eventually slides off.
The wax behind the polished surface does not melt.
Conclusion
The observation shows that dull black surfaces absorb
more heat than shiny or polished surfaces.
Experiment to show that dark surfaces are
good absorbers of heat and shiny surfaces
are poor absorbers of heat

87. HEAT ENERGY
Conduction happens in solid materials, when
vibrations
are passed on from particles to particles. There
must be a solid medium for the heat to be
transferred to.
Convection only happens in fluids where there
are molecules which can move around.
Radiation does not require any medium to
transfer heat, it can take place in a vacuum.
The differences between conduction,
convection and radiation