1

Temperature of a body

This is the degree or extent of coldness or

hotness of a body on some chosen scale.

Temperature is measured using an

instrument called thermometer.

It is a basic quantity and is measured in

degrees Celsius (0C) or Kelvin (K)

Kelvin (K) is the SI unit of temperature.

Temperature is a scalar quantity.

Expansion and Contraction of Solids

Metals and other solids expand when

heated and contract when cooled.

In simple terms,

Expansion is the increase in size of an

object when heated.

Contraction is the decrease in size of an

object when cooled.

Demonstration of expansion in solids

a.) The ball and ring experiment

Heat the ball and try to pass it through the

ring.

Leave it there for some time.

Observation

When both the ball and the rind are

at room temperature, the ball just

passes through the ring.

When the ball is heated it does not

go through the ring.

But when left there for some time,

it goes through.

Why?

When heated, the ball expands so that it

cannot go through the ring.

When left on the ring for some time, the

temperature of the ball decreases and it

contracts. At the same time, the

temperature of the ring increases and it

expands so that the ball goes through it.

b.) The bar and gauge apparatus

To investigate the force due so

expansion and contraction

Fit the tensioning nut and cast-iron pin in

the inside position of a bar-breaking

apparatus shown in figure (a). Tighten the

tensioning unit until there is no room for

expansion of the steel rod.

Heat the steel rod strongly and note what

happens to the cast iron pin.

Allow the apparatus to cool and repeat the

experiment with the cast iron pin on the

outside as shown in figure (b).

Withdraw the flame and allow it to cool.

You may pour cold water on it to cool it

faster. What happens lo the pin?

2

The cast iron pin breaks in both cases

Conclusion: The experiment shows that

very strong forces occur when metals

expand or contract due to heating and

cooling, respectively.

Expansion in gases also can result in very

strong forces, for instance the internal

combustion engines’ pistons are powered

by the expansion resulting from burning

fuel-air mixtures.

Applications of the expansion of solids 1. Construction of railway lines– an

expansion joint is allowed between any

two rails to accommodate expansion. A

fish plate is used to join two rails. Modern

railway system use the overlapping joint

at the end of rails.

2. Construction of bridges and roof tops

(steel girders)– for bridges one side has

rollers while the other is fixed to allow for

expansion. Concrete slabs are also laid on

the ground leaving space filled with pitch

to allow for expansion.

3. Hot water pipes– pipes carrying hot

water (steam) from boilers are fitted with

expansion joints for expansion.

3

4. Riveting – used to join two pieces of

metal together i.e. bimetallic strips, car

bodies, drums etc. Fitting rail cart wheel

using heat uses the principle of rivets.

Bimetallic

Bimetallic Strip.

ANOMALOUS EXPANSION OF

WATER

Solids and liquids expand on heating and

contract on cooling. Unlike other

substances, water has unusual behaviour.

As the temperature of water rises from 00C

to 40C, the volume of water falls showing

that water contract on heating from 00C to

40C.

At 40C, water has minimum volume.

After 40C, the volume of water rises as

heating continues.

A graph of volume against Temperature

Can you explain the meaning of

mass of a body?

Do you think the mass of water

change as its volume changes?

Write the equation relating mass,

volume and density.

As the volume of water reduces

then rises, does this have an effect

to its density?

Draw the graph of density against

temperature.

Effects of anomalous expansion of water.

Freezing of lakes and ponds.

In cold weather, when the

temperature of water falls below

00C, water in the lakes freezes and

ice is formed. So, how do fish

survive in frozen water? The

density of ice is less than that of

water and therefore stays at the top

and the water on the bottom remain

4

at 40C. This assists the aquatic

animals and plants to survive in

cold water.

Bursting of water pipes.

Water pipes can burst when water

flowing through the pipes freezes.

This is because on freezing the

volume of water increases.

Weathering of rocks. When

water freezes in the cracks of a

rock the volume of water increases.

This causes the rock to break into

small pieces resulting into

weathering of rocks.

Icebergs.

When water freezes to form ice, a

large mass of ice is immersed in

water and only its tip can be seen.

This can cause an accident to the

navigators.

Temperature

What is temperature?

Which instrument is used to measure

temperature of a body?

There are different types of a thermometer.

1. Liquid-in-thermometer

a.) Mercury thermometer

b.) Alcohol thermometer

c.) Clinical thermometer

2. Six’s maximum and minimum

thermometer

Liquid-in-glass thermometer

It uses either alcohol or mercury as

thermometric liquid.

Properties of thermometric liquid.

Visible.

Has a wide range of temperature

i.e. low freezing point and high

boiling point.

Do not stick on the walls of the

thermometer.

Sensitive to temperature change.

Expand uniformly.

Question

What are the advantages of using mercury

as a thermometric liquid than using

alcohol?

5

Calibration of a thermometer.

Thermometers must be calibrated before

they can be used to measure temperatures.

The calibration of an instrument refers to

the process of marking-up a scale on the

instrument to be used as measurement.

To produce a scale on a thermometer, two

fixed points must be determined first. Then

the two points must be the temperatures

which can easily and correctly be

reproduced in any part of the world.

On the Celsius scale, the two fixed

points are the ice point (0°C) and the

steam/boiling point (100°C).

The ice point (0°C), lower fixed point, is

the melting temperature of pure ice at

standard atmospheric pressure (760 mm

Hg).

The steam point (100°C), upper fixed

point, is the temperature of steam at

standard atmospheric pressure (760 mm

Hg).

After obtaining, the highest point and the

lowest point. We divide the length

between them to equal parts / scale.

Features of a thermometer

Bulb- the walls of the bulb is made

thin to make the thermometer more

sensitive to temperature change.

Capillary tube- it is made thin or

narrow to make the thermometer

more accurate i.e any slight

expansion or contraction of the

thermometric liquid is measurable.

Glass wall- it has a glass wall to

ensure:

a.) The reading is magnified

b.) Mechanical protection

c.) Easy reading because it is

clear.

During construction of the thermometer,

the following should also be considered:

The quantity of mercury in

the bulb is small so that the

mercury takes little time to

warm up.

The capillary tube is of

uniform cross-section so that

the mercury level changes

uniformly along its length.

6

Question

To determine the upper fixed point of a

thermometer, the thermometer is not put

in boiling water but in the steam.

Explain.

Clinical Thermometer.

Unlike ordinary thermometers which have

only the bulb, capillary tube and the stem;

clinical thermometers have constriction.

Constriction break the mercury thread

after the reading has been taken hence the

mercury in the tube stays back. After use,

the mercury in the tube can be forced

through the constriction back to the bulb

by flicking the thermometer.

The normal human body temperature is

370C .

7

A thermometer calibrated from 00C to

1000C is not required in the hospital.

Temperature scale conversion

The most commonly used temperature

scales are Celsius and Kelvin scales.

Celsius scale is also known as Centigrade

scale.

Fixed points:

For Celsius scale: 00C & 100

0 C

In Kelvin scale, the temperature of pure

melting ice is 273 K while that of pure

boiling water at normal atmospheric

pressure is 373 K.

Absolute zero temperature is the

temperature at which the energy of the

particles in a material is zero.

The lowest temperature in Kelvin scale is

0 K.

Change 0C to Kelvin.

T = Ɵ + 273

Where T= temp in kelvin

Ɵ = temp in 0C

Convert the following temperatures into

Kelvin.

a. 250C

b. 1000C

c. 00C

d. -2340C

e. 5600C

Convert the following temperatures into 0C

a. 350 K

b. 100K

c. 1K

d. 0K.

Six’s maximum and minimum

thermometer

8

It is used to record minimum and

maximum temperatures of a given place.

When the temperature of the surrounding

rises, the oil in the bulb A expands pushing

the mercury which in turn pushes up the

oil in the other arm. This compresses the

vapour above the oil and the maximum

index is pushed up to the maximum

position. This is the maximum

temperature.

When the temperature falls, the oil

contracts back into the bulb. Mercury

flows back pushing the minimum index to

the minimum position. This gives the

minimum temperature.

After taking the readings, the indices are

pulled down to the level of the mercury

using a magnet.

A bimetallic thermometer

It is made up of a coiled bimetallic strip

whose one end is fixed and the other end

connected to a pointer. Commonly used

metals are brass and invar. When the

temperature rises brass expands more than

invar. The strip thus curls forcing the

pointer to move over a calibrated scale.