NOTA FIZIK T4- HEAT

Concept Map Chapter 4

Heat

Dear students,

Success is the sum of small efforts, repeated day in and
day out.

Heat

Thermal Specific Heat Specific Gas Laws
Equilibrium Capacity Latent Heat

Q = mcθ Charles’ Boyle’s
Law Law

Specific Specific Pressure
latent heat of latent heat of Law
vaporisation
fusion
Q = mlv
Q = mlf

1

4.1 Thermal Equilibrium

The measure of the When an object is
degree of hotness of heated, it will absorb
heat energy and the
an object.
SI unit Kelvin, K temperature will
increase.
Temperature
Heat When an object is
A hot object is at a higher cooled, it will release
temperature than a cold • Form of energy heat energy and the
• Measured in
object. temperature will
Joules, J decrease.
Thermal contact
Net heat transferred
Two objects are in from hotter object
thermal contact when
(higher temperature)
heat energy can be to colder object (lower
transferred between
temperature).
them.

2

Heat transfer
When two objects with different degrees of hotness come into __t_h_e_rm__a_l_c_o_n_t_a_c_t,_______heat
energy is __tr_a_n_s_f_e_r_re_d____________between the two objects.

Mechanism of Thermal Equilibrium

Faster rate of heat
transfer from A to B

AB A BA B AB

Hot Cold Net flow of heat Heat transferred at No net heat transfer
from the hot object the same rate
Slower rate of heat to the cold object between A and B
transfer from B to A

• Heat energy is transferred at a faster _ rate • After some time, heat energy is transferred
at the same rate between the two
from the hotter object to the colder object. objects. There is no net heat transfer
between the objects.
Heat energy is also transferred from the
• The two objects are said to be in
colder object to the hotter one, but at a _th_e_r_m_a_l_e_q_u_il_ib_r_iu_m___________________ .

_sl_o_w_e_r___ rate. 3

• There is a net flow of heat energy

from the hotter object to the colder object.

• The hotter object cools down while the colder

object warms up .

Thermal Equilibrium ***
When two objects are in thermal equilibrium, there is no net flow of heat between them.
Two objects in thermal equilibrium have the same temperature.

Examples

1. A wet towel is placed on the forehead of a Cooling drinks
person who has high fever. 1. A hot drink can be cooled by

2. Initially the temperature of the cloth is lower than adding a few ice cubes to the drink.
the body temperature of the person. 2. Heat from the hot drink is

3. Heat energy is transferred from the forehead to transferred to the colder ice until
the towel until thermal equilibrium is reached. thermal equilibrium between the ice
and water is reached.
4. The towel is rinsed in tap water and the 3. The final temperature of the drink
procedure is repeated. equal the final temperature of ices.

5. In this way heat energy is removed from the
person.

Strength does not come from physical capacity. It comes

“ from an indomitable will.
”Mahatma Gandhi

4

The characteristic of the liquid used How a liquid-in-glass
in liquid-in-glass thermometer thermometer works?

1. be easily seen Liquid-in-glass 1. The bulb of the thermometer
2. expand and contract rapidly over a Thermometer contains a fixed mass of
mercury. The volume of the
wide range of temperature/ expand mercury increases when it
uniformly when heated absorbs heat.
3. not stick to the glass wall of the
capillary tube. 2. 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.

How can a thermometer be calibrated?

1. A temperature scale is obtained by choosing two temperatures, called the fixed point.
2. Definition of ice point and steam point

Fixed point Definition Value
0°C
Lower point: The temperature of pure melting ice 100°C
Ice Point
The temperature of steam from water that is boiling
Upper point: under standard atmospheric pressure.
Steam point

5

How can a thermometer be calibrated?

Steam L100 When the two fixed points have been marked on the stem of the
point thermometer, the range between them is divided equally into 100
divisions or degrees. The thermometer now has a scale.

L100

100 equal L0 Steam
divisions Ice
Boiling
Lθ water

Ice L0 Water Steam point
point Ice point

Bulb θ = Lθ − L0 100C
L100 − L0
6

Explain the working principle of a thermometer Thermometer

1. When the thermometer is placed in contact with hot water,
heat is transferred from hot water to the thermometer.

2. Thermal equilibrium between the thermometer and hot water
is reached when the net rate of heat transfer is zero.

3. The thermometer and the water are at the same temperature.
At this point, the thermometer reading shows the temperature
of the water.

What are characteristics of mercury that makes it suitable as a liquid-in-glass thermometer?

1. It is a good conductor of heat
2. It has a high boiling point, 357°C
3. It expands uniformly when heated
4. It is opaque (does not allow light to pass through) and it can be seen easily.
5. Mercury freezes at a temperature of - 39°C and it is therefore not suitable for measuring

temperatures below this temperature, such at the north pole.

How to increase the sensitivity of a mercury thermometer?

1. Thin capillary tube
2. A glass bulb with thinner wall
3. Small bulb

7

Exercise 4.1 Swami
Vivekananda
1. Which of the following characteristics is used in the
function of a liquid-in-glass thermometer?
A Volume of a fixed mass of liquid
B Boiling point of the liquid
C Resistance of the liquid
D Density of the liquid

2. Which of the following methods can be used to increase “Take up one idea. Make
the sensitivity of a mercury thermometer? that one idea your life -
A Thick-walled glass bulb
B Thinner capillary tube think of it, dream of it, live
C Shorter capillary tube
D Larger glass bulb on that idea. Let the brain,

3. An alcohol-in-glass thermometer has not been calibrated. muscles, nerves, every
When it is inserted into melting ice and boiling water, its
lengths are 5.2 cm and 13.7 cm respectively. part of your body, be full of
When it is inserted into a cup of warm water, the alcohol
length is 9.8 cm. Calculate the temperature of the warm that idea, and just leave
water.
A 44.12 °C every other idea alone.
B 52.22 °C
C 20.45 °C This is the way to success,
D 54.12 °C
that is way great spiritual

giants are produced ”

8

4.2 Specific Heat Capacity

Heat capacity, c
The amount of heat required to change its temperature by one degree.

Specific Heat capacity, c
The amount of heat that must be supplied to increase the temperature by 1 °C for a mass of
1 kg of the substance.

c = Q SI unit: = J kg-1°C-1
mθ
Q = heat absorbed / released, unit J
m = mass of the substance, unit kg
∆θ = temperature difference , unit °C

Quantity of heat absorbed or lost by Q = mc∆θ
a substance
900 J of heat needs to be supplied to 1 kg of Aluminium
What does specific heat of Aluminium to produce a 1 °C temperature increase.
900 Jkg-1°C-1 mean?

What does specific heat of water 4200 4 200 J of heat needs to be supplied to 1 kg of water to

Jkg1°C-1 mean? produce a 1 °C temperature increase.

9

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

A substance with 1. Heats up and cools at a faster rate. For example, metal like iron, steel,
a small value of copper and Aluminium is used as pots and pans because they can be
specific heat quickly heated up when there is only small heat absorption.
capacity
2. Sensitive to temperature changes a thermometer has low specific heat
capacities so it enables heat to be easily absorbed and released even
when small quantities of heat are involved.

A substance with 1. Heats up and cools at slower rate. Require more heat to raise its
a high value of temperature by a specific amount. Poor conductor of heat – handle of pot
specific heat
capacity 2. Can absorb a great amount of heat without a high increase in
temperature. For example, water acts a heat reservoir as it can absorb a

great amount of heat before it boils. Water is used as a cooling agent in a
car radiator.

“ When one makes the mind stick to one
thought, the mind becomes rock-steady and
the energy is conserved.

Ramana Maharshi 10

Applications of Specific Heat Capacity Aluminium body

Handle 1. Relatively low specific
1. Large specific heat capacity. heat capacity. The pot
becomes hot quickly.
T_h_e__h_a_n_d_le__w_il_l _n_o_t _b_e_co_m__e__to_o__h_o_t _
w__h_en__h_e_a_t_is__a_b_s_o_rb_e_d_.___________ 2. Low density so it will
_____________________________ be lighter
2. Poor conductor of heat.
3. Does not react with
Cooking pot the food in the pot

Copper base 11

1. Low specific heat capacity. The pot
becomes hot very quickly. This enables
quick cooking of the food in the pot.

2. High density. _T_h_e__h_e_av_i_e_r ___________
_ba_s_e__e_n_s_u_re_s__th_a_t_t_h_e_p_o_t_i_s_s_ta_b_l_e_______
_an_d__w_i_ll_n_o_t_to_p_p_l_e_o_v_e_r_e_a_s_il_y_. __________

Sea Breeze

• Land has a smaller specific heat capacity than

sea. Temperature of land increase faster than

sea. Therefore, land is warmer than the sea at

day time.
• Air above the land is heated up and rises.
• Cooler air from the sea moves from towards the

land as sea breeze.

Land Breeze

• At night, heat is lost from the land and sea.
• Sea has a larger specific heat capacity so sea is

warmer than land.
• Warmer air above the sea rises
• Cooler air from the land moves towards the sea

as land breeze.

12

Exercise 4.2

1. Calculate the total heat that is absorbed by a copper block of mass 500 g and which has been
heated from 31 °C to 80°C. (specific heat capacity of copper = 390 Jkg-1°C-1).
Ans : 38220 J

2. When an electric heater is supplied with an electric power of 2 kW to heat 4 kg of water for 1
minute, calculate the increase in temperature of the water. [specific heat capacity of water =
4 200 Jkg-1°C-1) .Assume there is no heat loss to the surroundings.

Ans : 7.15°C

Tips : Electric Energy, E = Pt = VIt Heat Energy, Q = mcθ 13

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 Jkg-1°C-1 and all heat produces is
absorbed by the bullet, what is the increase in temperature of the bullet?
Ans : 65°C

4. An aluminium 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 30 V and an ammeter which gives a reading of 2.5A, calculate the specific
heat capacity of the aluminium.

Ans : 900 JKg-1°C-1

Tips : Kinetic Energy, E = ½ mv2 Heat Energy, Q = mcθ 14

5. 300 g of water at temperature 40 °C is mixed with 900 g of water at temperature 80°C. If there
is no heat loss to the surroundings, what is the final temperature when thermal equilibrium is
achieved by the mixture of water?

Ans : 70°C

Tips : Heat Energy Released = Heat Energy Absorbed 15

4.3 Specific Latent Heat

Latent heat
The heat absorbed or the heat released at constant temperature during change of phase.

1. When a solid melts at its melting point, latent heat of fusion is absorbed 4 main

2. For a liquid to solidify at its freezing point, latent heat of fusion is released. Changes of

3. When a liquid is boiling at its boiling point, latent heat of vaporization is phase

absorbed.

4. When vapour condenses back into the liquid phase, latent heat of

vaporization is released.

GAS

MELTING BOILING

Latent heat Latent heat
absorbed absorbed

SOLID Latent heat LIQUID Latent heat
released released

SOLIDIFICATION CONDENSATION

The common characteristics of the four processes in the change of phase 16

1. A Substance undergoes a change of phase at a particular temperature.
2. Heat energy is transferred during change of phase
3. During change of phase, the temperature remains __c_o_n_s_ta_n_t___ even though there is

transfer of heat.

Heating Curve State : Liquid State : Gaseous
Temperature : Increases Temperature : Increases
State : Solid
Temperature : Increases Liquid heated to its boiling The temperature of the
point gas will increase to the
Solid heated to its melting temperature of the source
point
F
Temperature

Boiling Point D E
C
Melting Point B

A

State : Solid and liquid Time
Temperature : Unchanged
State : Liquid and gas
B : Solid start melting Temperature : Unchanged
B – C : Solid melting
C : Solid melted completely D : Liquid start boiling
D – E : Liquid boiling
F : Liquid boiled completely

17

Cooling Curve Draw a cooling curve.

State : Gaseous State : Liquid
Temperature : Decreases Temperature : Decreases

The temperature decreases as The liquid is cooled to its
heat is released to the freezing point.
surrounding.
State : Solid and liquid
Temperature Temperature : Unchanged
S : The solid start freezing
P S – T : The liquid freezing
T : The liquid freezes completely
Boiling Point QR
U
Freezing Point ST
Time
State : Liquid and gas State : Solid
Temperature : Unchanged Temperature : Decreases
The solid is cooled to the room
Q : The gas start condensing temperature.
Q – R : The gas condensing
R : The gas condenses completely 18

Why does the temperature remains constant during change of phase?

1. During change of phase, the transfer of heat does not cause a change in the kinetic energy of
the molecules.

2. 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 among each
other.

3. When a liquids boils, the heat absorbed is used to completely break the bonds between the
particles and also to do work against atmospheric pressure when the gaseous vapour expands
into the atmosphere.

Specific Latent Heat, l
The amount of heat required to change the phase of 1 kg of the substance at a constant
temperature.

l=Q Unit : J kg-1
m Q = latent heat absorbed or released by the substance

m = mass of the substance

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

19

Specific latent heat of vaporization
The amount of heat required to change 1 kg of the substance from the liquid to gaseous
phase without a change in temperature.

Specific latent heat of fusion of ice is Specific latent heat of vaporization of water
336 000 Jkg-1 is 2.26 x 106 Jkg-1

336 000 J of latent heat is needed for 1 kg ice 2.26 x 106 J of latent heat is needed for 1 kg
to melt to become water at 0 °C water to boil to become vapour at 100°C

Formula to Q = mcθ Q = Pt = ml Q = ml
calculate
The heat added or as as
HEAT removed changes the
If heat is supplied When the heat added
Condition temperature of an electrically or removed changes
object, the heat is the phase of an object
calculated using
at constant
temperature, the heat is

calculated using

P = power of the heater, unit in W,
t = time , unit is seconds

20

Exercise 4.3 2. An electric kettle contains 3kg of water.
Calculate the amount of heat required to
1. The specific latent heat of fusion of ice is boil away all the water after the boiling
336 000 Jkg-1. What is the quantity of heat point has been reached.
required to melt 2.5 kg of ice at 0 °C? Ans : 6.78 x 106 J

Ans : 840000 J

Specific latent heat of fusion of ice is 336 000 Jkg-1 21
Specific latent heat of vaporization of water is 2.26 x 106 Jkg-1
Specific heat capacity of water is 4.2 x 103 J kg-1°C-1

3. What is the quantity of heat that is required to convert 4g of ice into steam at 100°C.
Ans : 12064 J

Specific latent heat of fusion of ice is 336 000 Jkg-1 22
Specific latent heat of vaporization of water is 2.26 x 106 Jkg-1
Specific heat capacity of water is 4.2 x 103 J kg-1°C-1

1 The freshness of fish and meat can be maintained
by placing them in contact with ice. With its larger
Drinks can be cooled by adding
in several cubes of ice. When 2 latent heat, ice is able to absorb a large quantity of
ice melts a large amount of heat
is absorbed and this lowers the heat from the fish as it melts. Thus, food can be
temperature of the drink. kept at a low temperature for an
extended period of time.

Applications of Specific
Latent Heat

3 4 Always be very careful when

Water has a large specific latent opening the lid of a pot when the
heat of vaporization. This property water in it is boiling. Water has a
enables steam to be used for large specific latent heat of
cooking by the method of vaporization. When steam
steaming. When steam condenses on the skin of your
condenses on the food, the latent arm, the very large amount of
heat is released directly onto the latent heat released can cause a
food enables the food to be serious burn.
cooked at a faster rate.
23

4.4 Gas Laws Charles’ law Pressure Law

Boyle’s Law states that for a fixed mass states that for a fixed mass
of gas, the volume of the of gas, the pressure of the
states that for a fixed mass gas, V is directly gas, P is directly
of gas, the pressure of the proportional to its absolute proportional to its absolute
gas, P is inversely temperature, T when its temperature, T when its
proportional to its volume, pressure, P is kept volume, V is kept constant.
V when the temperature, T constant.
is kept constant.

P 1 P1V1 = P2V2 V T V1 = V2 P T P1 = P2
V T1 T2 T1 T2
P P
P V

V 1 T P/T T
PV PV V V/T V/T P/T

VP VT PT

24

25

Boyle’s Law Charles’ law Pressure Law

1. When the volume of a 1. When a gas is heated, the 1. When a gas is heated,

gas is decreased, the average kinetic energy of the average kinetic

number of molecules the molecules increases . energy increases .

per unit volume Temperature of the gas The temperature of the

increases . increases. gas increases.

2. Rate of collision between 2. The faster moving

2. The same number of the molecules and the molecules strike the
molecules moves in a
smaller space. walls will increase if walls of the container

3. The molecules collide the volume is constant. more frequently .
more frequently
with the walls of the 3. If the gas is allowed to 3. Thus, the pressure of
container.
expand, the faster the gas increases .
4. This increase in the
rate of collision results molecules now move in a
in an increase in
the pressure exerted by bigger space.
the gas.
4. Therefore, the rate of

collision between the

molecules and the walls

remain constant and

thus the pressure is

constant. 26

Absolute temperature P P
Temperatures measured in the Kelvin, K

VV

T/K θ / °C T/K θ / °C

-273 -273
0K 0K

Convert °C to Kelvin: Convert Kelvin to °C :
θ + 273 T – 273

Absolute zero At this point:
1. Voume and pressure of gas is zero
The lowest possible temperature 2. Kinetic energy of the gas molecules is zero
3. Gas molecules are stationary.
which is ___-_2_7_3_°_C___o_r__0__K________.

Human beings unlike plants and animals have the capacity to choose what they want to

be. I belief that if a child elects to be a brilliant and successful person he has the innate,

God-given talents to achieve whatever he desires. There are absolutely no obstacles to

his ambition except himself. 27

Exercise 4.4

Question 1 Question 2
The air in a foot pump has an initial volume The pressure of a bubble under the sea is 120
of 2800 cm3 and pressure 100 kPa. The cm Hg. When the bubble rises to the surface
outlet of the pump is closed and the piston of the sea, its volume becomes 25.0 cm3.
pushed inwards until the volume of the air Assuming that the atmospheric pressure is 76
becomes 700 cm3. What is the pressure of cm Hg, what is the original volume of the
the compressed air in the pump? bubble?

Ans : 400 kPa Ans : 15.83 cm3

28

Question 3 Question 4
A cylinder contains 200 cm3 of gas at a A fixed mass of gas in an enclosed metal
temperature of 27°C. The gas is heated until container has a pressure of 2.5 x 105 Pa. If the
its temperature increases by 30°C. If the gas is heated from 27°C to 87°C, calculate the
piston of the cylinder expands under constant final pressure of the gas.
pressure, what is the final volume of the gas?
Ans : 300 kPa
Ans : 220 cm3

29

Challenge Zone

1. As shown in Figure 1 , block P of mass 7 kg at 90°C and block Q of mass 3 kg at 30°C . Given
that the specific heat capacity of P is 4 900 J kg-1°C-1 and the specific heat capacity of Q is
3800 J kg-1°C-1 .Block P and Q are contact with each other. Assume that there is no energy loss
to the surroundings.

7 kg (a) What is the final temperature of P and Q if they
are in thermal equilibrium?

(b) Find the energy given by P during the process.
P 3 kg Give the answer in unit of kJ.
(c) Find the energy absorbed by Q during the
Q process. Give the answer in unit of kJ.

90°C 30°C

Figure 1 Ans : (a) 75.03C (b) 513.47kJ (c) 513.34kJ

30

2. There are two beakers of water each with mass 500 g and 1 200 g respectively. The water is
then mixed together by pouring the water into another beaker. If the initial temperature of 500g
water and 1 200g water are 38°C and 88°C respectively.
(a) Determine the final temperature of the mixture of water after achieved equilibrium.
(b) State the assumption used in your calculation.
Ans : (a) 73.29 °C (b) No heat loss to the surroundings

31

3. The graph of temperature-time in Figure 2 is T/°C Graph of temperature
obtained when a solid is heated by a heater of
power 500 W. Determine against time
(a) the melting point of the solid. 75
(b) the latent heat of fusion of the substance.

Ans : (a) 75 °C (b) 900 J

0 0.2 t/s

2.0

Figure 2

32

4. Figure 3 shows a gas trapped inside a tube by 7 cm of 7 cm Mercury
mercury. The length of the gas column at 20°C is 23 cm. Gas
Determine the length of the air column at temperature
90°C.

Ans : 28.49 cm

23 cm at
20°C

Figure 3

33

5. Diagram 4 shows an ice cream container used by an ice cream seller using his 34
motorcycle.

Diagram 4

Table 1 shows the specification of four types of ice cream containers P, Q, R and S, that can
be used by an ice cream seller to carry ice cream.

You are required to determine the most suitable ice cream container to carry ice cream.
Study the specification of the four types of ice cream container based on the given aspects.
Explain the suitability of the each aspects.

[10 marks]

Box P Q R S

Specific heat capacity of ice cream box High High Low Low

Size of ice cream box Large Small Small Large
Material of outer box Copper PVC PVC Aluminium
Colour of outer box Bright Bright
Dark Dark
Answer : Table 1

35

Characteristics Explanation
Easy get cold // becomes cool quickly
Low specific heat capacity of ice
cream box Easier to carry // easy too become cold
Smaller size of ice cream box

Plastic PVC Poor conductor of heat

Bright colour of outer box Does not absorb heat from surrounding quickly

R is chosen because Low specific heat capacity of ice cream
box, Smaller size of ice cream box, Plastic PVC,
Bright colour of outer box