4.1 THERMAL EQUILIBRIUM

CHAPTER 4
HEAT

4.1 THERMAL EQUILIBRIUM

TEXT BOOK : PAGE 120 - 124

SUE ROSE





4.1.1 Explain with examples thermal
equilibrium in daily life

When a cold metal spoon is
put into a cup of hot coffee,
the spoon and the coffee are
said to be in thermal contact.

Heat energy can be
transferred between the two
bodies.
How can the metal spoon
cool down the hot coffee?

What is the final condition of the spoon and the coffee?

Heat energy can be transferred between two objects
when they are in contact (sentuhan)

Thermal contact is not What kind of contact?
only physical touch
Thermal Contact!
(Sentuhan terma)

When two objects are in thermal contact, the temperature of the hot
object will drop while the temperature of the cold object will rise
until the temperature of both objects become the same

Pemindahan haba
bersih sifar

Net heat transfer between the
two objects becomes zero

Both objects are said to be in
thermal equilibrium

Keseimbangan terma!

A boy feels the
heat of the
kettle. Why?

The ice melt
when it is in
the boy’s hand.
The boy’s hand
is cooled. Why?

The boy takes his hand
away from the kettle
because the boy feels the
heat of the kettle

Heat is transferred from the
kettle to the boy’s hand

HEAT is transferred from
HOT object to COLD object

The ice melt when it is in
the boy’s hand
The boy’s hand is cooled

Heat is transferred from the
boy’s hand to the ice

HEAT is transferred from
HOT object to COLD object



HEAT is a form of ENERGY

TEMPERATURE is the
DEGREE OF HOTNESS

SI UNIT : KELVIN (K)

Comparison between Temperature & Heat

characteristic Temperature Heat

Defination Degree Energy
of hotness

SI unit KELVIN (K) JOULE (J)

Measuring Thermometer Calorimeter
device
Base Derived
Base @ quantity quantity
Derived
quantity?

When an object Heat absorbed Temperature rises
is heated or released? or drops?

When an object HEAT Temperature
is cooled absorbs increases

Heat Temperature
releases decreases

Activity 1 Aim: To show thermal equilibrium between two bodies in thermal
contact

Apparatus : Two retort stands, two thermometers, 250 ml beaker (A), 50 ml
beaker (B), measuring cylinder, stop-watch, hot water 50 ⁰C, tap water & tissue

Activity 1 Aim: To show thermal equilibrium between two bodies in thermal
contact

1. Wrap beaker A with tissue and fill it with 150 ml of tap water.
2. Fill 40 ml of 50⁰C hot water into beaker B.

3. Place beaker B into beaker A. Then, place thermometer A and thermometer
B into beaker A and beaker B respectively.

4.Record readings of thermometer A and thermometer B every 30 s until the
readings of both thermometers are the same.

Temperature of Temperature of

Time, t/s thermometer A / ⁰C thermometer B / ⁰C

0 27 50
30.0 28 48
60.0 29 46
90.0 30 44
120.0 31 42
150.0 32 41
180.0 33 40
210.0 34 39
240.0 35 39
270.0 36 38
300.0 37 37

1. Why is beaker A wrapped with tissue paper?

To prevent heat absorbs from
surroundings.

2. Describe the changes in temperature of the hot
water and tap water.

When the two water are in thermal
contact, the temperature of the hot
water decreases while the
temperature of tap water
increases until the temperature of
both objects become the same.

3. What causes the changes in temperature?

➢ Hot water releases heat to
tap water.

➢ Tap water absorbs heat from
hot water.

➢ Transfer of heat occurs when
two bodies are in thermal
contact.

4. Discuss the transfer of heat between the hot water
in beaker B and the tap water in beaker A

Heat is transferred from hot water
in the beaker to the tape water with
high rate.

Heat is transferred from the tape
water to the water in the beaker
with low rate.

5. State the direction of net heat transfer between the two objects.

The direction of net Temperature hot water
heat transfer is from hot decrease; heat released.
water in beaker B to tap Temperature of tap water
water in beaker A. increases, heat absorbed

6. Compare the temperature of both
thermometer after 5 minutes

The temperature of both
thermometer are equal

7. What happens to rate of heat
transfer after 5 minutes?

Heat is transferred at the same rate
between the hot water in beaker B to
tap water in beaker A

8. What can you say about the net rates of
transfer of heat when the readings of
the two thermometers become equal?

There is no net heat transfer
between both readings.
The net rates of heat transfer is
zero.

Both hot water and tap water are
in a state of thermal equilibrium.

➢ THERE IS NO NET FLOW OF HEAT BETWEEN

TWO OBJECTS
➢ TWO OBJECTS HAVE THE SAME

TEMPERATURE

Thermal Equilibrium in Daily Life

(a) A wet towel is placed on the forehead of a
person who has high fever.

• Initially the temperature of the cloth is
lower than the body temperature of
the person.

• Heat energy is transferred from the
forehead to the towel until thermal
equilibrium is reached.

• The towel is rinsed in tap water and
the procedure is repeated. In this way
heat energy is removed from the
person.

Thermal Equilibrium in Daily Life

(b) Cooling drinks

• A hot drink can be cooled by adding
a few ice cubes to the drink.

• Heat from the hot drink is
transferred to the colder ice until
thermal equilibrium between the ice
and water is reached.

• Ices cubes melt. The temperature of
the drink decreases and the drink
cools.

Thermal Equilibrium in Daily Life

(c) Cooling object in the refrigerator

• When food is kept in the
refrigerator, heat from the food
flows to the air in the refrigerator
until thermal equilibrium occurs.

• Temperature of the food drops
and the food stays fresh for a
longer period.

Thermal Equilibrium in Daily Life

(d) Baking cake in an oven

• Hot air in oven is in thermal
contact with cake batter.

• Heat from the hot air flows
to the cake batter.

• This causes the cake batter
to be heated until it is
baked.

Thermal Equilibrium in Daily Life

(e) Taking temperature of a sick
patient

• Clinical thermometer is placed
under the tongue of a patient.

• Heat from the patient’s body flows
to the thermometer until thermal
equilibrium occurs.

• The temperature of the patient and
the thermometer become the same.

• The body temperature of the patient
can be determined

4.1.2 Calibrate a liquid-in-glass thermometer
using two fixed points

A thermometer that
does not have a scale
can be calibrated using
two fixed temperature
points.
Two fixed points used
for distilled water ae
melting point of ice, 0 ⁰C
and boiling point of
water 100 ⁰C

State what happens to the liquid in the capillary
tube of thermometer when heat is absorbed?

The liquid will expand.

What does the length of the liquid column in the
capillary tube indicate?

Indicates the magnitude of the
temperature.

Calibration is a process of
making a scale of reading on a

thermometer.

0⁰C is the fixed lower limit
100⁰C is the fixed upper limit

The length of liquid column
between the fixed lower limit and
the fixed upper limit is divided into

100 equal divisions

The thermometer is then calibrated and can be used
to measure temperature between 0⁰ and 100⁰C

The process of Example: length of
calibrating uses column of liquid
the thermometric expands when
property of liquids temperature
increases.
in glass

Thermometric
property means a
physical property

which can be
measured which

changes with
temperature

How a thermometer is calibrated?

At the scale of degree Celsius, two fixed temperature are chosen.

Lower point / Ice point Upper point / Steam point

Melting point Boiling point of water at
of pure ice. atmospheric pressure of 1 atm

0 ⁰C 100 ⁰C



Aim: To calibrate a liquid-in-glass
thermometer using boiling point of distilled
water and melting point of ice

Apparatus: Thermometer, ruler, 250 ml beaker, immersion heater, power supply,
retort stand, ice, distilled water, masking tape

1. Cover the scale of the thermometer with masking tape so
that the scale cannot be seen.

2. Fill beaker A with ice and a small amount of distilled water.

3. Put a thermometer into beaker A. Wait until
there is no more change in the level of liquid
column.

4. Then, mark the level of liquid column on the

stem of the thermometer. Label this level as 0 ⁰C.

5. Fill beaker B with distilled water and put in an
immersion heater.

6. When the distilled water in beaker B is boiling,
put the thermometer into beaker B. Wait until
there is no more change in the level of liquid
column.

7. Then, mark the level of liquid column on the stem
of the thermometer. Label this level as 100 ⁰C.
Switch off the immersion heater.

8. Measure the length from 0 ⁰C to the 100 ⁰C mark

as L100

9. Prepare beaker C and fill it with tap water.

10. Put the calibrated thermometer into beaker C.
Wait until there is no more change in the level of
the liquid column.

11. Then, mark the level of the liquid column on the
stem of the thermometer. Label this level as θ⁰C

12. Measure the length from the 0⁰C mark to the
θ⁰C mark as Lθ

13. Calculate the temperature of tap water using
the formula,

1. The bulb of the thermometer should not touch the base or
side wall of the beaker while taking measurement. Explain.

To prevent heat lost through the beaker to
the surroundings.

2. Why should you wait until there is no more change in the
level of the liquid column before making a mark on the
stem of the thermometer?

To make sure that the thermal equilibrium
state is reached.

temperature of the liquid
Length of the capillary at temperature ϴ.
length of the capillary at ice point
length of the capillary at boiling point



THE END