The document discusses heat and thermal equilibrium. It defines key terms like temperature, heat, and thermal contact. It explains that when two objects at different temperatures come into contact, heat is transferred from the hotter object to the cooler one until they reach the same temperature and thermal equilibrium. Examples are given like a wet towel being used to reduce a fever by transferring heat from the body. The document also discusses specific heat capacity and how it relates to how fast an object's temperature changes when heat is gained or lost. Specific heat capacities of different materials are provided.

1. Physics
(Form 4)
Chapter 4: HEAT

2. 4.1 Understanding Thermal
Equilibrium

3. Definition
Definition
Temperature The measure of degree of hotness of an object.
SI unit: Kelvin, K
Heat A form of energy.
SI unit: Joules, J
Eg: Heat is transferred from a hotter object
(higher temperature) to a cooler object (lower
temperature).
Thermal
contact
Two objects are in thermal contact when heat
energy can be transferred between them.
Heat transfer When two objects with different degree of
hotness come into thermal contact, heat energy
is transferred between these two objects.

4. Mechanism of thermal equilibrium
• Heat energy is transferred at a
faster rate from the hotter
object to the cooler object.
• Energy is also transferred from
the cooler object to the hotter
object, but at a much slower
rate.
• There is a net flow of energy
from the hotter object to the
cooler object.

5. • The hotter object cools down,
while the cooler object warms
up.
• After some time, energy is
transferred at the same rate
between the two objects.
• There is NO net heat transfer
between the objects.
• These two objects are said to be
in thermal equilibrium.

6. Thermal equilibrium
• When two objects are in thermal equilibrium,
there is ___________________________
between them.
• Two objects in thermal equilibrium have the
_________ temperature.

7. Example of application of thermal
equilibrium in daily lives
Wet towel & fever
• Wet towel is places on your forehead when you
have fever.
• Initially, temperature of the cloth is lower the
your body temperature.
• Heat energy is transferred from ____________ to
______________ until
____________________________ is reached.
• The towel is then rinsed and the procedure
repeats.
• This way, heat energy is removed from you.

8. Cooling drinks
• Ice cubes are added to a hot drink.
• Heat from the ______________ is transferred
to the ____________ until
________________________ is reached.
• The final temperature of the drink is the same
as the final temperature of the ice cubes.

9. Liquid-in-glass thermometer
• Characteristics of liquid used:
– Easily seen
– Expand and contract rapidly and uniformly over a
wide range of temperature
– Does not stick to the glass wall of the capillary
tube

10. How does it work?
• The bulb of the thermometer contains a fixed
mass of mercury. The volume of mercury
increased when it absorbs heat.
• The mercury expands and rises in the capillary
tube.
• The length of the mercury column in the
capillary tube indicates the magnitude of the
temperature.

11. How is a thermometer calibrated?
• A temperature scale is obtained by choosing 2
temperature, called fixed points.
Fixed point Definition Value
Ice point Temperature of
pure melting ice
00C
Steam point Temperature of
steam from
boiling water
under standard
atmospheric
pressure.
1000C

12. • When two fixed points have been marked on
the stem of the thermometer, the range
between them is divided equally into 100
divisions. The thermometer now has a scale.

13. Working principle of a thermometer
• When the thermometer is placed in contact with
hot water, heat is transferred from the hot water
to the thermometer.
• Thermal equilibrium between the thermometer
and the hot water is reached when the net rate of
heat transfer is _______.
• The thermometer and the water are at the same
temperature.
• At this point, the thermometer reading shows the
temperature of the water.

14. Characteristics of mercury
1. Good heat conductor.
2. High boiling point, 3570C.
3. Expands uniformly when heated.
4. Opaque and can be easily seen.
**Freezing point of mercury is -390C. Therefore
is is not suitable for measuring temperatures
below this temperature, like in the north pole.

15. How to increase sensitivity of mercury
thermometer?
1. Thin capillary tube.
2. Glass bulb with thin wall.
3. Large bulb.

16. 4.2 Understanding specific heat
capacity

17. Definitions
• Heat capacity, C:
– The amount of heat required to change the temperature
of an object by 10C.
• Specific heat capacity, c:
– The amount of heat required to increase 1kg of
substance by 10C.
Quantity of heat absorbed
or lost by a substance:

18. What does specific heat capacity of
aluminium 900 J/kg 0C mean?
900 J of heat energy needs to be supplied to 1kg
of aluminium to produce a 10C temperature
increase.

19. What does specific heat capacity of
water 4200J kg-1 0C-1 mean?
Answer:

20. Physical meaning of specific heat
capacity, c
• When two objects of the equal mass are
heated at equal rates, the object with smaller
specific heat capacity will have a faster
temperature increase.
• When two objects of the equal mass are left
to cool down, the temperature of the object
with smaller specific heat capacity will drop
faster.

21. Substance with small value of specific
heat capacity
1. Heats up and cools down at a faster rate.
– Eg: Metals like iron, steel, copper and aluminum
are used as pots and pans between they can be
quickly heated up when there is only small heat
absorption.
2. Sensitive to temperature change.
– Eg: A thermometer has low specific heat
capacity. It enables heat to be easily absorbed
and released even when small quantities of heat
are involved.

22. Substance with high value of specific
heat capacity
1. Heats up and cools down at a slower rate.
Requires more heat to raise its temperature
by a specific amount.
– Poor heat conductor  handle of pot/pan
2. Can absorb a great amount of heat without a
high increase in temperature.
– Water: used as a cooling agent in a car radiator.

23. Application of specific heat capacity
Cooking pot:
1. Copper base:
– Low specific heat capacity. The pot becomes hot very quickly,
enables quick cooking of food.
– High density. Heavier base ensures that the pot is stable and
will not topple easily.
2. Wooden handle:
– Large specific heat capacity. Poor heat conductor: handle will
not become too hot when heat is absorbed.
3. Aluminum body:
– Relatively low specific heat capacity. Pot becomes hot very
quickly.
– Low density.
– Does not react with food in the pot when heated.

24. Sea breeze: (daytime)
• Land has smaller specific heat capacity than
the sea.
• In daytime, land has a faster increase in
temperature. Land is warmer than the sea.
• Air above the land is heated up and rises.
• Cooler air from the sea moves towards the
land as sea breeze.

25. Land breeze: (Nighttime)
• At night, heat is lost from the land and sea.
• The sea has a larger specific heat capacity,
release heat slower, therefore the sea is
warmer than the land.
• Warm air above the sea rises.
• Cooler air from the land moves to the sea as
land breeze.

26. Cooling system of car engine:
Water is cheap and has a
____________________________________. Therefore, it is a
preferred cooling agent.
A water pump circulates the water inside the engine. Heat
produced by the engine is __________________ by the water
that flows along the space in engine walls. The hot water then
flow to the radiator where heat is lost to the cooler air that
flows through the cooling fan.

27. A boy drinks the hot soup with a spoon. If he
accidentally spills a spoonful of soup onto his hand,
he would only experience slight pain.
But if he spills the whole bowl of soup onto himself,
he would suffer serious injury.
Why?
• The mass of the spoonful of soup is smaller than the
mass of a bowl of soup, although both have the
same temperature and the same specific heat
capacity.
• .
• Mass is directly proportional to the quantity of heat.
• Soup in the bowl contains more heat.

28. Example 1:
• Calculate the total heat that is absorbed by a copper
block of mass 500g which has been heated from 31˚C
to 80˚C.
[Specific heat capacity of copper = 390 J kg-1 ˚C-1]

29. Example 2:
• When an electric heater is supplied with an electric
power of 2kW to heat 4kg of water for 1 minute,
calculate the increase in temperature of the water.
[specific heat capacity of water = 4200 J kg-1 ˚C-1]
Assume there is no heat loss to the surrounding.

30. Example 3:
• A lead bullet moves horizontally with a velocity of 130 ms-1
and embedded into a cement wall after collision. If the
specific heat capacity of lead = 130 J kg-1 ˚C-1 and all the
heat produces is absorbed by the bullet, what is the
increase in temperature of the bullet?

31. Example 4:
• An aluminum block of mass 1 kg is heated by an electric
heater for 3 minutes and a temperature rise of 15˚C is
recorded. If the electric heater is connected to a voltmeter
which gives a reading of 30V and an ammeter which gives a
reading of 2.5A, calculate the specific heat capacity of
aluminum.

32. Example 5:
• 300g of water at temperature of 40˚C is mixed with 900g
of water at temperature of 80˚C. Assuming there is no
heat loss to the surrounding, what is the final
temperature when thermal equilibrium is achieved by
the mixture of water?

33. 4.3 Understanding specific latent
heat

34. Latent heat
• Definition: The heat absorbed or the heat
released at constant temperature during
change of phase.

35. 4 main changes of phase
Melting:
When a solid melts, latent
heat of fusion is absorbed
but the temp remains
constant at its melting
point.
Solidification:
For a liquid to solidify
at its freezing point,
latent heat of fusion
has to be removed.
Boiling:
When a liquid is boiling, latent
heat of vaporization is
absorbed but the temp remains
constant at its boiling point.
Condensation:
When vapour condenses
back into liquid, latent of
vapourization is released.

36. A
B
C
D
E
Heating graph

37. A
• PQ: Solid heated to its melting point.
• Heat energy: Absorbed
• Temperature: Increases
• State of matter: No change
• Contents: Solid

38. B
• Q: Solid begins to melt
• QR: Solid is melting
• S: Entire solid has melted
• Heat energy: Absorbed
• Temperature: Constant
• State of matter: Solid to liquid
• Contents: Solid and liquid

39. C
• RS: Liquid heated to its boiling point
• Heat energy: Absorbed
• Temperature: Increases
• State of matter: No change
• Contents: Liquid

40. D
• S: Liquid begins to boil
• ST: Liquid is boiling
• T: Entire liquid has boiled away
• Heat energy: Absorbed
• Temperature: Constant
• State of matter: Liquid to gas
• Content: Liquid and gas

41. E
• TU: Gas is heated
• Heat energy: Absorbed
• Temperature: Increases
• State of matter: No change
• Contents: Gas

42. Cooling graph
A
B
C
D
E

43. A
• PQ: Gas cools down to its boiling point
• Heat energy: Released
• Temperature: Decreases
• State of matter: No change
• Content: Gas

44. B
• Q: Gas begins to condense
• QR: Gas condenses
• R: Entire gas has condensed
• Heat energy: Released
• Temperature: Constant
• State of matter: Gas to liquid
• Content: Gas and liquid

45. C
• RS: Liquid cools down to its freezing point
• Heat energy: Released
• Temperature: Decreases
• State of matter: No change
• Content: Liquid

46. D
• S: Liquid begins to freeze
• ST: Liquid is freezing
• T: Entire liquid has freeze
• Heat energy: Released
• Temperature: Constant
• State of matter: Liquid to solid
• Content: Liquid and solid

47. E
• TU: Solid cools down
• Heat energy: Released
• Temperature: Decreases
• State of matter: No change
• Content: Solid

48. Common characteristics of the 4
processes in the change of phase
1. Substance undergoes a change of phase at a
particular temperature (melting point, boiling
point, freezing point)
2. Heat energy is transferred during change of
phase.
3. During change of phase, TEMPERATURE
REMAINS THE SAME even though there is
transfer of heat.

49. Notes
**Temperature of a substance is proportional to
the average kinetic energy of its particles.**
1. Temp increases when the average kinetic
energy of the particles increase.
2. Temperature ___________ when the average
kinetic energy of the particles ___________.
3. Temperature remains constant when the
average kinetic energy does not change.

50. Why does temperature remain
constant during change of phase??
• During change of phase, the transfer of heat
does not cause a change in the kinetic energy of
the molecules.
• During melting, the heat absorbed is used to
break up the bonds between the particles. The
particles are freed from their fixed positions and
are able to vibrate and move.
• During boiling, heat absorbed is used to break
the bonds between the particles and to work
against the atmospheric pressure when gaseous
vapour expands into the atmosphere.

51. Specific latent heat, l
• Definition: Amount of heat required to change
the phase of 1kg of a substance at a constant
temperature.

52. Specific latent heat of fusion
• The amount of heat required to change
1kg of a substance from solid to liquid
phase without a change in temperature.

53. Specific latent heat of
vaporization
• The amount of heat required to change
__1kg___ of substance from ___liquid___
to ___gas____ phase without
__change______ in temperature.

54. Specific latent heat of fusion of ice is
33600 J kg-1.
Explanation:
33600 J of latent heat is needed for 1kg of ice
to melt to become water at 0˚C.

55. Specific latent heat of vaporization of
water is 2.26x106 J kg-1.
Explanation:

56. • When the heat added or removed changes the
temperature of an object, heat is calculated using:
• When the heat added or removed changes the phase of an
object at CONSTANT TEMPERATURE, heat is calculated
using:
• When heat is supplied electrically:
– Q = Electrical energy = Pt
– P = power of heater in Watt, W
– t = time, in seconds, s
Can also be
written as,
Pt = ml

57. Example 1:
• The specific latent heat of fusion of ice is 33600 J
kg-1. What is the quantity of heat required to melt
2.5kg of ice at 0˚C?

58. Example 2:
• An electric kettle contains 3kg of water. Calculate
the amount of heat required to boil away all the
water after the boiling point has been reached.
[Latent heat of vaporization of water = 2.26x106 J kg-1]

59. Example 3:
• What is the quantity of heat that is required to convert 4g of
ice into steam at 100˚C?
[specific latent heat of vaporization of water is 2.26x106 J kg-1 ;
specific latent heat of fusion of ice is 33600 J kg-1 ;
specific heat capacity of water = 4.2x103 Jkg-1 ˚C-1]

60. Application of specific latent heat
1. Drinks can be cooled by adding ice cubes. When ice
melts, a large amount of heat is absorbed, this lowers
the temperature of the drink.
1. Freshness of fish and meat is maintained by keeping
them with ice. Ice absorbs heat from the fish as it
melts, thus food can be kept longer.
1. Cooking by steaming. Water has a large specific latent
heat of vaporization. When steam condenses on the
food, latent heat is released directly onto the food,
enabling food to be cooked at a faster rate.

61. 4. Our bodies are cooled down after sweating. Latent
heat of vaporization is absorbed from the body
when sweat evaporates. Heat is removed from the
body.
5. When water is boiling in a pot, always be careful
when opening the lid. Water has a large specific
latent heat of vaporization. When steam condenses
on our skin, large amount of latent heat release
can cause serious burn.

62. 4.4 Understanding GAS LAW
1. Boyle’s law
2. Charles’ law
3. Pressure law

63. Boyles’ law
• States that for a fixed
mass of gas, the pressure
of the gas, P is inversely
proportional to its
volume, V when the
temperature, T is kept
constant.

64. • When the volume of a gas in decreased, the
number of molecules per unit volume increase.
• The same number of molecules move in a smaller
space.
• The molecules collide more frequently.
• The increase of rate of collision increases the
pressure exerted by the gas.

65. Charles’ law
• States that for a fixed mass of gas, the volume
of the gas, V is directly proportional to its
absolute temperature, T when its pressure, P
is kept constant.

66. • When a gas is heated, the average kinetic energy of the
molecules increases. The temperature of the gas increases.
• The rate of collision between the molecules and the walls will
increase if the volume is constant.
• If the gas is allowed to expand, the faster molecules move in
a bigger space.
• Therefore, the rate of collision between molecules and the
wall remain constant and the pressure remain constant also.

67. Pressure’s law
• States that for a fixed mass of gas, the
pressure of gas, P is directly proportional to its
absolute temperature, T when its volume, V is
kept constant.

68. • When a gas is heated, the average kinetic
energy increases. The temperature of the gas
increases.
• The faster moving molecules strike the walls
of the container more frequently.
• Thus, the pressure of the gas increases.

69. Universal gas law

70. Absolute temperature
• Temperature measured in Kelvin, K.
• Convert ˚C to K: x + 273
• Convert K to ˚C: x - 273
Absolute zero
• The lowest possible temperature which is -273˚C or 0 K.
• 0 K = -273˚C
• At this point:
– Volume and pressure of gas is zero
– Kinetic energy of gas molecules is zero
– Gas molecules are stationary.

71. Example 1:
• The air in a foot pump has an initial volume of 2800 cm3
and pressure 100kPa. The outlet of the pump is closed
and the piston pushed inwards until the volume of the air
becomes 700cm3. What is the pressure of the
compressed air in the pump?

72. Example 2:
• The pressure of a bubble under the sea is 120 cm Hg.
When the bubble rises to the surface of the sea, its
volume becomes 25.0 cm3. Assuming that the
atmospheric pressure is 76 cm Hg, what is the original
volume of the bubble?

73. Example 3:
• A cylinder contains 200 cm3 of gas at a temperature of
27˚C. The gas is heated until its temperature increases by
30˚C. If the piston of the cylinder expands under constant
pressure, what is the final volume of the gas?

74. Example 4:
• A fixed mass of gas in an enclosed metal container has
a pressure of 2.5x105 Pa. If the has is heated from 27˚C
to 87˚C, calculate the final pressure of the gas.

76. Universal gas law: