Oasis Science and Technology 7

Activity 8 Bell Hammer
Bucket
Objective: To demonstrate that sound
propagates through a liquid Water
Materials required: A bucket, water, a bell,
a hammer Figure 8.11
Procedure: Take a bucket and fill it with
water.
Immerse a bell into the water of the bucket
and hit the bell with a hammer. Can you
hear the sound? What can you conclude
from this activity?

8.7 Speed of Sound in Different Media

The speed of sound in solids is maximum and the speed of sound in gases is
minimum. This is because the molecules are packed closer in solids than in the
gases (or air). Since the molecules of a medium carry vibrations, they do so faster
when they are closer together.

8.8 Factors Affecting the Speed of Sound in Air

The factors that affect the speed of sound in air are as follows:

(i) Density
The speed of sound decreases when the density of air increases and the
speed of sound increases when the density of air decreases. For example,
the density of oxygen is more than the density of hydrogen. So, the speed of
sound in hydrogen is more than that in oxygen.

(ii) Temperature
The speed of sound in air increases when the temperature increases. This
is because when the temperature increases the density of air decreases and
consequently, the speed of sound travels faster on a hot summer day than on
a cold winter day.

(iii) Humidity
The amount of water vapour present in air is called humidity. The presence
of water vapour decreases the density of air. Therefore, the density of sound
increases when the humidity increases and vice-versa. The speed of sound in
moist air is more than that in dry air. For example, sound travels faster on a
rainy day than on a dry day.

PHYSICS Oasis School Science and Environment - 7 93

(iv) Wind
The speed of sound in air is affected by the direction of wind. If the wind
blows in the same direction in which the sound travels, the speed of the
sound increases. Conversely, the speed of sound decreases if the wind blows
in the opposite direction in which the sound travels.

Summary

• Sound is a form of energy which produces a sensation of hearing in the
ears. Sound is produced due to the vibration of bodies.

• Sound cannot travel through a vacuum. It can travel through the solids,
liquids and gases.

• An object which produces sound is called a source of sound.

• Wave motion is a periodic disturbance travelling through a medium
which is produced by a vibrating body.

• During a wave motion, the medium does not move as a whole but only
the disturbance travels through the medium.

• Waves are of two types transverse wave and longitudinal wave. Sound
travels in the form of longitudinal waves.

• The wave in which the particles of the medium vibrate up and down
perpendicular to the direction of the wave is called a transverse wave.

• A transverse wave consists of crests and troughs. Crest is the point of
maximum positive displacement of a transverse wave.

• The wave in which the particles of the medium vibrate to – and – fro
(back and forth) in the direction of the wave is called a longitudinal wave.

• The transmission of sound from one place to another is called propaga-
tion of sound.

• Density, temperature, humidity and direction of wind affect the speed of
sound in air.

Exercise

1 Choose the best answer form the given alternatives.

a. The form of energy that produces a sensation of hearing is ______.

(i) sound (ii) light

(iii) heat (iv) electricity

94 Oasis School Science and Environment - 7 PHYSICS

b. Which of the following is required to produce sound?

(i) solid medium (ii) vibration of a body

(iii) liquid medium (iv) gas medium

c. Sound cannot propagate through ______.

(i) gas (ii) liquid

(iii) vacuum (iv) solid

d. The speed of sound in steel is ______.

(i) 1500m/s (ii) 5200m/s

(iii) 232m/s (iv) 2500 m/s

e. The speed of sound is maximum in ______.

(i) liquid (ii) solid

(iii) gas (iv) water

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. Sound is produced due to the vibration of a body.

b. Sound can travel faster in gases than in solids.

c. Sound wave is a longitudinal wave.

d. The speed of sound increases when the density of air decreases.

3 Fill in the blanks using appropriate words.
a. When a body vibrates, ………….. is produced.
b. Sound needs a ………….. for propagation.
c. Sound wave propagates in the form of ………….. wave.
d. A ………….. wave consists of crests and ………….. .
e. The speed of sound in air increases when the temperature ………….. .

4 Answer the following questions.
a. What is sound? How is it produced?
b. What is a source of sound? Give any three examples.
c. What is a wave? Name two types of wave.
d. What is a transverse wave? Give any two examples.
e. What is a longitudinal wave? Give any two examples.
f. What is meant by propagation of sound?
g. What are the factors that affect the speed of sound in air?
h. Why is the speed of sound more in solids than in gases?
i. What is the speed of sound in air?
j. Write down the effect of humidity and temperature on the speed of sound.

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5 Differentiate between:
a. Transverse wave and Longitudinal wave
b. Crest and Trough
c. Compression and Rarefaction

6 Give reason.
a. Sound cannot travel through a vacuum.

b. The speed of sound is higher in solids than in liquids.

c. Astronauts cannot hear each other on the surface of the moon.

d. The speed of sound in hydrogen is higher than that in oxygen.

7 Describe an activity to demonstrate that sound is produced due to vibration.

8 Describe an activity to prove that sound travels through a solid medium.

9 Describe an experiment to demonstrate the propagation of sound through a
liquid medium.

96 Oasis School Science and Environment - 7 PHYSICS

Unit Estimated teaching periods: Th Pr
3 1
9
Magnet

Magnet

Objectives

After completing the study of this unit, students will be able to :

• introduce magnet and differentiate between natural magnet and artificial
magnet.

• state the utilities of magnets.
• explain and demonstrate the methods of making magnets.

Course of Study

• Introduction to magnet
• Types of magnets
– Natural and artificial magnets
– Permanent and temporary magnets
• Uses/Utilities of magnets
• Methods of making magnets
– Rubbing method
– Electrical method

Points to be Focused / Questions to be Discussed

• What is a magnet?
• What are natural and artificial magnets?
• What are temporary and permanent magnets?
• Why are magnets used?
• How are magnets made?

PHYSICS Oasis School Science and Environment - 7 97

9.1 Introduction

A magnet is a substance which has the property of
attracting iron, cobalt, etc. The substances like iron, S N

cobalt, nickel, etc. which are drawn towards the magnet

are called magnetic substances and the force that the Fig. 9.1: Bar magnet

magnet exerts on magnetic substances is called the

magnetic force. The discovery of a magnet is attributed to a shepherd boy, Mangers,

who while roaming on Mt. Ida, found that his iron-strapped sandals got stuck to the

mountain. He could not walk easily and tried to find the cause of the problem. A

wise man found that the mountain was made of black stone with iron in it which

had a special property to attract iron. That black stone was an ore of iron called

magnetite. The stone was called lodestone. It was used by navigators for finding

their way in the sea. In our daily life, magnets are widely used in electric appliances
such as loud speakers, electric motors, dynamos, toys, etc.

Magnets are of two types: natural magnets and artificial magnets.

9.2 Natural Magnets

Naturally occurring substances like lodestone which attract magnetic substances
are called natural magnets. Natural magnets are found in irregular shapes and
their magnetism (i.e. attracting force) is not strong enough to be used in modern
magnets.

9.3 Artificial Magnets

Magnets made by human beings using artificial methods are called artificial
magnets. Artificial magnets are of various shapes and sizes. Some of them are as follows:

(i) Bar magnet (ii) Horse shoe-shaped magnet

(iii) U-shaped magnet (iv) Magnetic compass

(v) Magnetic needle (vi) Cylindrical magnet

Some of the artificial magnets are shown below:

Bar magnet Horse shoe-shaped magnet Compass U-shaped magnet

Fig. 9.2: Magnets of various shapes

attribute /əˈtrɪbjuːt/ - to say or believe that sth is the result of a particular thing
roam / rəʊm / - to walk or travel round an area without any definite aim or direction

98 Oasis School Science and Environment - 7 PHYSICS

Artificial magnets are of two types. They are temporary magnets and permanent
magnets.

9.4 Temporary Magnets

The magnets that can retain Switch Coil Battery
their magnetism only for a
short time are called temporary Insulated
copper wire

magnets. These magnets are Steel bar Iron nails
usually made of soft iron or
steel by passing electric current Figure 9.3: Temporary magnet

through an insulated wire. They lose their magnetism when the flow of electric
current is stopped. Electromagnet is an example of a temporary magnet. Temporary
magnets are used in electric bell, electric motor, electric fan, generator, etc.

9.5 Permanent Magnets

The magnets that can retain their magnetism for a long time are called permanent
magnets (fig. 9.2). These magnets are made of steel, cobalt, iron, nickel, etc. These
magnets are used in speaker, transistor, radio, tape recorder, etc.

Activity 1 Fig. 9.4

• Bring a bar magnet near a heap of iron dust. What
do you observe? You will notice that the magnet
draws the iron dust towards it.

• Bring some iron filings and spread them on a sheet
of paper. Roll a bar magnet on the filings and pick
up the magnet. What do you observe? What can you
conclude from this activity?

Activity 2

• Bring a bar magnet and tie it with a nylon thread. Suspend it in a stand
so that it rotates freely. Observe it for a while till it comes at rest. Does the
magnet come at rest by pointing north-south direction?
Now, turn the direction of the magnet by your hand and observe the
direction in which the magnet resettles.
What can you conclude from this activity?

retain /rɪˈteɪn/ - to keep sth; to continue to have sth 99
PHYSICS Oasis School Science and Environment - 7

9.6 Uses of Magnets

(i) Magnets are used in loudspeakers, radios, generators, dynamos, electric
motors, computers and telephones.

(ii) Magnets are used in magnetic compasses, refrigerator doors, pencil boxes, etc.
(iii) Magnetic tapes are used in tape recorders and video recorders.
(iv) Magnets are also used in certain toys to give a magic effect.

9.7 Methods of Making Magnets

Now-a-days magnets of desired shapes and sizes can be made artificially by using
magnetic substances. There are many methods of making magnets. Some of the
simple and common methods are described below:

1. Rubbing method

Magnetic property can be developed in a magnetic substance by rubbing a bar
magnet for several times over the magnetic substance. It can be done by two methods.

a. Single touch method: In this method, a S Bar magnet
single magnet is rubbed with a magnetic N
substance for several times in only one
direction. While rubbing the magnet, we
should use the same pole every time. With
Steel bar

the help of this method, iron bar, blade, iron Fig.. 9.5: Single touch method
clips, etc. can be magnetized.

Activity 3

• Bring a steel bar and keep it horizontally on the table. Bring a bar magnet
and rub it on the steel bar in only one direction from one end of the steel
bar (fig. 9.5). Please note that we should use the same pole of the magnet
from only one end of the steel bar. Repeat this process for 40-50 times.

• Now, bring the steel bar near the iron nails. What do you observe? Does
the steel bar show magnetic property?

b. Double touch method: In this Bar magnet N S Bar magnet
method, a pair of magnet is rubbed S N
with a magnetic substance for
several times. In this process, we
should rub the magnetic substance
at the centre with the unlike poles Steel bar
Figure 9.6: Double-touch method

of two magnets simultaneously (fig. 9.6). After rubbing for 30-40 times, the
magnetic substance develops magnetic properties.

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2. Electrical method
Temporary magnets can be prepared by passing electric current in the coil around a
magnetic substance. In this method, a coil of insulated copper wire is wound around
the magnetic substance and the two ends of the wire are connected to an electric
source. When the current flows through the coil, the magnetic substance becomes
a magnet. The magnet made by using electric current is called an electromagnet.
It is a temporary magnet because its magnetism can be switched on or off when
required.

Switch Coil Battery Insulated
copper wire

Steel bar Iron nails
Figure 9.7: Electrical method
Figure 9.3: Temporary magnet

When the current in the coil is switched off, the electromagnet loses its magnetism
and it no longer behaves as a magnet.

Precautions while making an electromagnet

i. An insulated copper wire should be used for making the coil in an
electromagnet. Short circuiting takes place if we use a naked copper wire
instead of insulated wire.

ii. The winding should be done starting from only one side.
iii. The strength of an electromagnet can be increased by increasing the number

of turns in the coil, by increasing the amount of electric current in the coil and
by using a soft magnetic substance.
Electromagnets are used in electric bells, loud speakers, fans, electric motors,
telephone devices, etc. Similarly, electromagnets are used for lifting heavy
loads and to separate magnetic substances from non-magnetic substances.

Activity 4

• Bring a two metre long insulated copper wire and wind it around a steel
bar for several times.

• Connect the two ends of the copper wire to a battery through a switch.
• Keep some iron nails near the steel bar and turn the switch ‘ON’. What do

you observe? Does the steel bar attract iron nails?
• Now, turn the switch ‘OFF’ and observe carefully. Does the steel bar attract

nails? Why ? What can you conclude from this activity?

electromagnet /ɪˌlektrəʊˈmaɡnɪt/ - a piece of iron which becomes magnetic when electricity is
passed through it

PHYSICS Oasis School Science and Environment - 7 101

Summary

• A magnet is a substance which has the property of attracting iron, cobalt, etc.

• In our daily life, magnets are widely used in electric appliances such as loud
speakers, electric motors, dynamos, toys, etc.

• Naturally occurring substances like lodestone which attract magnetic
substances are called natural magnets.

• Magnets made by human beings using artificial methods are called artificial
magnets.

• The magnets that can retain their magnetism only for a short time are called
temporary magnets.

• Now-a-days magnets of desired shapes and sizes can be made artificially by
using magnetic substances.

• Electromagnets are used in electric bells, loud speakers, fans, electric motors,
telephone devices, etc.

Exercise

1 Choose the best answer from the given alternatives.
a. A magnet attracts ______.

(i) plastic (ii) stone

(iii) wood (iv) iron

b. A freely suspended bar magnet always rests in direction.

(i) east – west (ii) north-south

(iii) west – south (iv) south – east

c. Which of the following is a natural magnet?

(i) lodestone (ii) bar magnet

(iii) magnetic compass (iv) U-shaped magnet

d. Which of the following is a temporary magnet?

(i) magnetic needle (ii) electromagnet

(iii) bar magnet (iv) compass

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2 Tick (√) the correct statement and cross (×) the incorrect one.

a. The substance that attracts iron, nickel, etc. is called magnet.

b. A freely-suspended bar magnet always rests in east-west direction

c. U-shaped magnet is a natural magnet.

d. A permanent magnet is used in loud speakers.

3 Fill in the blanks using appropriate words.
a. Magnet was discovered by ………..
b. Lodestone is a ……….. magnet.
c. The man- made magnet is called ……….. .
d. The magnet made by using ……….. is called electromagnet.
e. Magnetic tapes are used in ……….. and ………..

4 Answer the following questions.
a. What is a magnet?
b. What is meant by magnetism?
c. What is a natural magnet? Give one example.
d. What is an artificial magnet? Give any three examples.
e. What is a temporary magnet?
f. What is a permanent magnet? Name any three devices in which permanent
magnet is used?
g. What is an electromagnet? Name any three devices in which it is used.
h. Write any two methods of making magnets.
i. How is magnet made by an electrical method? Explain.
j. Write any three uses of magnets.

5 Describe an activity to prove that electromagnet is a temporary magnet.
6 Differentiate between:

a. Natural magnet and Artificial magnet

b. Permanent magnet and Temporary magnet
c. Bar magnet and Electromagnet

7 Name any three devices in which magnets are used.

8 Name any three magnetic and three non-magnetic substances used in your home.

PHYSICS Oasis School Science and Environment - 7 103

Unit Estimated teaching periods: Th Pr
3 1
10
Electricity

Electricity

Objectives

After completing the study of this unit, students will be able to :

• introduce and demonstrate static electricity and explain its effects.
• draw electric circuits and introduce the symbols used in electric circuits.
• demonstrate the methods of connection of cells and explain its

importance.

Course of Study

• Static electricity
• Effects of static electricity
• Current electricity
• Electric circuit and its types
• Symbols used in electric circuit

Points to be Focused / Questions to be Discussed

• What is static electricity? How is it produced?
• What are the effects of static electricity?
• What is current electricity?
• What is electric circuit? What are its types?
• What are the symbols used in electric circuits?
• What is combination of cells? What are its types?

104 Oasis School Science and Environment - 7 PHYSICS

10.1 Introduction

When a plastic comb is brought near a piece of paper, Comb
it does not attract the paper. If the comb is first rubbed
on dry hair and then brought near the piece of paper, it
attracts the paper. From this observation, we can say that
initially the comb is electrically neutral, i.e. the number
of protons is equal to the number of electrons in it, and
hence shows no effect on the piece of paper. When we rub Paper

the comb on dry hair, the flow of electrons starts and the
comb becomes electrically charged. It is because electrons Fig. 10.1 A comb attracting a
flow from our hair to the comb and it becomes negatively piece of paper
charged. As the negatively charged comb is brought near the paper, the positive
charges of the paper get deposited near the comb. This process helps to attract the
paper since opposite charges attract and similar charges repel each other.

The electricity developed in the comb is one example of static electricity. The electric
charges produced by friction which remain bound to the surface of an insulator and
do not flow is called static electricity. In static electricity, electric charges remain
at rest.

10.2 Causes of Static Electricity

Substances are made of atoms that are electrically neutral as they contain equal
number of positive charges (protons) and negative charges (electrons). The
phenomenon of static electricity requires a separation of positive and negative
charges. When two materials are in contact, electrons may move from one material
to another which leaves an excess of positive charge on one material and an equal
negative charge on the other. When these materials are separated, they retain this
charge imbalance. So, static electricity is also an imbalance of electric charges within
or on the surface of a substance.

10.3 How a Body is Charged by Friction

Every substance has equal number of protons
and electrons. Protons are positively charged and
electrons are negatively charged particles. The + Electron
protons are present in the nucleus of an atom and +
the electrons revolve around it. It is not possible Nucleus
to transfer protons from one substance to another ++ Neutron
because protons are strongly held in the nucleus of ++ Proton

Shell

the atom. On the other hand, electrons are loosely
bound by the atom. So, when we rub one body over Fig. 10.2: A neutral atom
another body, friction is developed which produces
heat energy. This energy is responsible for the transfer of electrons from one body
to another. The substance which gains electrons will be negatively charged due to
its higher number of electrons than that of the protons. The substance which loses

PHYSICS Oasis School Science and Environment - 7 105

electrons has excess protons. So it will be positively charged. In this way, friction
helps to charge different substances. A body is said to be positively charged if it
has deficiency of electrons. Similarly, a body having excess of electrons is called
negatively charged.
Charges develop in various insulators or non-metals like plastic, wool, nylon,
polyster, acrelyc, etc. due to friction. When we wear clothes made of wool, nylon,
polyster, acrelyic, etc. charges develop on those clothes due to friction with our
body. When these clothes are put off, charges move and a sound like ‘tik-tik’ can be
heard and flashes can be seen in a dark room.

10.4 Effects of Static Electricity

There are many effects of static electricity.
The effects of static electricity are familiar
to most people because people can feel,
hear and even see the spark. Lightning and
thunderstorm are the dramatic natural effects
of static electricity. Lightning is a bright flash
of electricity produced by a thunderstorm. It is
a massive electrostatic discharge between the
electrically charged regions within the clouds Figure: 10.3: Lightning

or between a cloud and the surface of the earth. The charged regions within the
atmosphere temporarily equalize themselves through lightning flash.

There are three types of lightning from a cloud to itself, from one cloud to another
and between a cloud and the ground. Although lightning is always accompanied
by the sound of thunder, distant lightning can be seen but it is too far away for the
thunder to be heard.

Lightning primarily occurs when warm air is mixed with cold air masses, resulting
in atmospheric disturbances necessary for polarizing the atmosphere. The positively
and negatively charged air masses proceed in opposite directions, positive upwards
within the clouds and negative towards the earth.

The electrons move from negatively charged cloud to the positively charged cloud.
A large amount of heat is produced when charges transfer suddenly from one
cloudmass to another. This heat makes the surrounding air quite hot that appears
as a flash in the sky. Similarly, the hot air moves in the form of wave towards the
path of electricity and contracts immediately in the form of wave which produces a
sound that we hear soon after lightning.

Thunderstorm

A thunderstorm is a storm with lightning and thunder. It is produced by the
cumulonimbus cloud, producing strong winds, heavy rainfall and sometimes
hail. Thunderstorms can occur throughout the year but they are most likely
to happen in spring and summer and during afternoon and evening hours. All

thunderstorm /ˈθʌndəstɔːm/ - a storm with thunder and lightning

106 Oasis School Science and Environment - 7 PHYSICS

thunderstorms produce lightning and are
very dangerous. Thunderstorm damages
life and property. It kills humans, animals
and destroys houses, buildings, towers,
trees, etc. An American scientist Benjamin
Franklin was the first person to prove
that in a thunderstorm the clouds are
electrically charged.

During a thunderstorm, clouds gather
charges. When two masses of clouds with
unlike charges come near each other,
there can be a very heavy flow of charges Fig. 10.4: Thunderstorm

between them. This causes energy to be released in the form of light, heat and
sound. This is the lightning we see and the thunder we hear during a storm. A
lightning discharge may be very dangerous. It can cause fire, kill living beings and
shatter buildings.

10.5 Lightning Conductor

Lightning conductor is used to protect
tall buildings from damage by lightning.
It consists of a tall rod of copper or iron
with a number of sharp pointed long
rods at the top end. The lower end of
the lightning conductor is connected to
a metallic plate which is buried in the
ground.
In rainy season, roofs of tall buildings Figure: 10.5: A lightning conductor used in a house
are wet so they become good conductors of electricity. When a negatively charged
thunder cloud passes over the tall building fitted with a lightning conductor, the
charge is induced on the pointed tips of the conductor. When a lightning strikes, the
charge is conducted down into the earth via the thick metal rod. Thus, the building
is saved from the possible damage.

10.6 Current Electricity

Current electricity is a form of energy produced due to the continuous flow of
electrons through a conductor. Every atom is made up of two types of charged
particles. They are protons (positively charged particles) and electrons (negatively
charged particles). Metallic conductors such as copper, aluminium, etc. contain a
large number of free electrons. When these electrons flow continuously in a certain
direction, electric current is produced.
Electricity is one of the major sources of energy. It can easily be converted into light
energy, heat energy, sound energy, magnetic energy, and so on.

PHYSICS Oasis School Science and Environment - 7 107

10.7 Sources of Electricity

In modern world, we use a large number of electronic appliances such as computer,
television, radio, camera, washing machine, refrigerator, calculator, watch, etc.
Electrical energy is required to operate these appliances. Similarly, electrical energy
is essential to run industries, to operate fans, to obtain light, heat, etc. The devices
from which we obtain electricity are called sources of electricity. The three major
sources of electricity are as follows:

1. Cell 2. Photo cell or Solar cell 3. Dynamo or Generator

In order to use electrical energy, electricity should flow through a certain path
which is called electric circuit.

Copper wire

10.8 Electric Circuit Switch

An electric circuit is a path made by connecting Dry cell
a cell, a conducting wire and a bulb. It is a
continuous path through which current flows Bulb
(fig. 10.6). The things required for making an
electric circuit are described below: Fig. 10.6

a. Cell or Battery: It acts as the source of electricity.

b. Conducting wire: It is the medium through which electric current flows.

c. Bulb: A bulb is a device which converts electrical energy into heat energy and
light energy. A bulb is also called a load. It shows the effect of electric current.

d. Switch: It is a device which is used to open or close an electric circuit.

Open circuit and Closed circuit

When the switch is turned ‘OFF’, the bulb does Copper wire
not glow. Such electric circuit is called open
circuit (fig. 10.7). In such condition, the current Dry cell Switch
cannot flow continuously through the wire. So a off
load cannot function when the circuit is opened.
Bulb

When the switch is turned ‘ON’, the bulb glows. Fig. 10.7: Open circuit
Such electric circuit is called closed circuit. In
such condition, electricity flows continuously Copper wire Switch
through the circuit. As a result, the bulb glows on
(fig.10.8). Dry cell
In our home, school or office, electric circuits Bulb glowing
are closed to light the bulbs or operate other
appliances. Electric circuits are closed or Fig. 10.8: Closed circuit
opened with the help of switches fixed on the
switch boards.

dynamo /ˈdaɪnəməʊ/ - a device for turning mechanical energy into electricity

108 Oasis School Science and Environment - 7 PHYSICS

10.9 Symbols Used in Circuit Diagrams

When we draw circuit diagrams, it is very difficult to draw various components
used in the electric circuit. For the sake of convenience, various components used in
an electric circuit are represented by their symbols. Symbols of various components
which are often used in an electric circuit are given below:

S. No. Components Symbol Function
1. Cell + Source of electric current

2. Battery +– Source of electric current

3. Switch To put the current on or off in the
4. Bulb circuit
To produce light

5. Wire +A– To make a conducting path
6. Ammeter To measure the current

7. Voltmeter +V– To measure the voltage
8. Galvanometer G
To detect the current
9. Load or Resistance
To convert electrical energy into
other forms of energy like heat and
light

Above mentioned components are connected in an A
electric circuit in the given method. V

Fig. 10.9

Activity 1
Above mentioned components are connected in an electric circuit as shown in the
gi•ven figTcouaprkepe.ear dry cell, electric bulb, switch, bulb holder and conducting wire or
wire. Connect them as shown in the fig. 10.7.

• Study the characteristics of open circuit and closed circuit.

• Does the bulb glow when the switch is turned ‘off’, why?

• Write down the conclusion of this activity.

10.10 Combination of Cells

We use cells for various purposes in our daily life as the source of electricity. Some
times we need low voltage and sometimes we need high voltage. To get different

PHYSICS Oasis School Science and Environment - 7 109

voltage, we need to connect the cells in different ways. There are two types of
combination of cells. They are:

(i) Series combination of cells

(ii) Parallel combination of cells

(i) Series combination of cells: If the positive terminal of the first cell is connected to
the negative terminal of the second cell and positive terminal of the second cell is
connected to the negative terminal of the third cell and so on, the combination is
called series combination of cells. In this combination, the brightness of the bulb
increases with the increase in the number of cells and vice–versa. The group of cells
combined in a series is called battery.

1.5 V 1.5 V 1.5 V 1.5 V 1.5 V 1.5 V

+
–
+
–
+
–

+
–
+
–

+
–

(a) (b) (c)
Fig 10.10: Series combination of cells

In series combination of cells, the total voltage is equal to the sum of the voltage of
the individual cells, i.e.

Total voltage (V) = V1 + V2 + V3 + .......

Similarly, the current increases when the number of cells is increased in the series
combination. This type of combination is done when more voltage and more current
is required.

(ii) Parallel combination of cells: If the positive terminals of all cells are connected to
a common point and all the negative terminals are connected to another common
point in a circuit, the combination of cells is called parallel combination. In such
combination, the brightness of the bulb does not increase on increasing the number
of cells. However, the bulb glows for a longer time in parallel combination.

+ ++ + ++
1.5V 1.5V 1.5V 1.5V 1.5V 1.5V

– –– – ––

Fig 10.11: Parallel combination of cells

In parallel combination of cells, the total voltage of the circuit is equal to the voltage
due to each cell, i.e.

Total voltage (V) = V1 = V2 = V3

110 Oasis School Science and Environment - 7 PHYSICS

Similarly, the total current in circuit of parallel combination is the sum of current
through each cell. This combination is used when low voltage and high current is
required.

Activity 2

• Take any 3 dry cells, combine them in series as well as in parallel and
observe the brightness of the bulb.
In parallel combination, brightness of the bulb remains constant but in
series, brightness increases with the increase in the number of cells.

Summary

• The electric charges produced by friction which remain bound to the surface of
an insulator and do not flow is called static electricity.

• The phenomenon of static electricity requires a separation of positive and
negative charges.

• The substance which gains electrons will be negatively charged due to its
higher number of electrons than that of protons.

• A body is said to be positively charged if it has deficiency of electrons. Similarly,
a body having excess of electrons is called negatively charged.

• A thunderstorm is a storm with lightning and thunder.

• A lightning discharge may be very dangerous. It can cause fire, kill living
beings and shatter buildings.

• Lightning conductor is used to protect tall buildings from damage by lightning.

• Current electricity is a form of energy produced due to the continuous flow of
electrons through a conductor.

• The devices from which we obtain electricity are called sources of electricity.

• An electric circuit is a path made by connecting a cell, a conducting wire and a
bulb.

• If the positive terminal of the first cell is connected to the negative terminal
of the second cell and positive terminal of the second cell is connected to the
negative terminal of the third cell and so on, the combination of cells is called
series combination.

• If the positive terminals of all cells are connected to a common point and all
the negative terminals are connected to another common point in a circuit, the
combination of cells is called parallel combination.

PHYSICS Oasis School Science and Environment - 7 111

Exercise

1 Choose the best answer from the given alternatives.

a. The electricity produced due to friction between two insulators is ....................

(i) current electricity (ii) electric current

(iii) voltage (iv) static electricity

b. Which of the following is the effect of static electricity?

(i) thunderstorm (ii) cloud formation
(iii) lighting bulb (iv) ringing bell

c. Which of the following is used to protect tall buildings from thunder?

(i) battery (ii) lightning conductor
(iii) lightning radio (iv) electric wire

d. Which of the following is the symbol of resistance?

(i) (ii)
(iii) (iv) + –

e. Which of the following is an electric load?

(i) battery (ii) cell
(iii) bulb (iv) switch

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. The electricity developed in a comb is static electricity.

b. Lightning is the effect of current electricity.

c. Thunderstorm does not affect life and property.

d. In a closed circuit, a load does not function.

e. In series combination of cells, the brightness of bulb decreases on
increasing the number of cells.

3 Fill in the blanks using appropriate words.
a. Electricity is a form of ..................................

b. .................................. is a bright flash of electricity.

c. .................................. is used to protect tall buildings from lightning.

d. A load functions in .................................. circuit.

e. Brightness of the bulb .................................. on decreasing the number of cells
in series combination.

112 Oasis School Science and Environment - 7 PHYSICS

4 Answer the following questions.
a. What is static electricity? How is it produced?

b. How are charges developed due to friction?

c. How does lightning occur in the sky?

d. What do you mean by thunderstorm? How does it occur?

e. What is lightning conductor? Why is it useful?

f. What is current electricity?

g. Define an electric circuit with a neat figure.

h. What are two types of electric circuit?

i. Why are symbols used in an electric circuit?

j. What is meant by series combination of cells? Write down its two features.

k. What is meant by parallel combination of cells? Write down its two features.

5 Differentiate between:
a. Static electricity and Current electricity

b. Open circuit and Closed circuit

c. Series combination of cells and Parallel combination of cells

6 Draw the symbols of the given electric appliances.

a. Battery b. Resistor

c. Bulb d. Switch

e. Voltmeter f. Ammeter

7 Draw an open electric circuit having a switch, a bulb and three cells in parallel
combination.

8 Describe an activity to demonstrate that the brightness of the bulb increases on
increasing the number of cells in series combination.

PHYSICS Oasis School Science and Environment - 7 113

Unit Estimated teaching periods: Th Pr
9 1
11

Balloons

Matter

Objectives

After completing the study of this unit, students will be able to :

• describe general states of matter (solid, liquid and gas) and explain their properties.
• tell the names and symbols of first twenty elements, i.e. from atomic number 1 to 20.
• define compounds and write the molecular formulae of some common

compounds.
• introduce atom and molecules and explain the method of writing molecular

formula.
• define physical and chemical change and differentiate between them.

Course of Study

• States of matter (solid, liquid and gas)
• Element – introduction, names and symbols of the first 20 elements
• Compound–introduction and examples
• Differences between element and compound
• Atom, molecule and molecular formula
• Physical change and chemical change

Points to be Focused / Questions to be Discussed

• What is matter? What are three states of matter?
• What are properties of solids, liquids and gases?
• What are elements and compounds?
• What are symbols and molecular formulae?
• What are atoms and molecules?
• What are physical change and chemical change?

114 Oasis School Science and Environment - 7 CHEMISTRY

11.1 Introduction

We see a variety of substances around us. Air, water, soil, stone, plastic, animals,
plants, etc. are some examples of matter. It is because they have mass and they
occupy space. Anything which has mass and volume is called matter. But light,
sound, shadow, etc. do not have mass and volume. So they are not called matter.

Matter can exist in three physical states: solid, liquid and gas. Matter can be soluble
or insoluble. They can be good conductor or bad conductor of heat and electricity.
Matter can be transparent, translucent or opaque. Similarly, matter can be changed
from one state to another.

11.2 States of Matter

Matter can exist in three different states. They are solid, liquid and gas. For example,
stone and wood are solids, milk and water are liquids and oxygen and carbon
dioxide in atmosphere are gases.

Matter

Solid Liquid Gas



Solid

The matter which has a fixed shape and a
fixed volume is called a solid. Stone, brick,
iron, ice, steel, rock, book, sand, wood, etc.
are some common examples of solids. The
solids have the following characteristics.

(i) Solids have a fixed shape. Brick Book
(ii) Solids have a fixed volume.
(iii) Solids do not flow. Figure 11.1: Some solids

(iv) Solids cannot be compressed, because their molecules are closely packed.
(v) Solids are generally hard.

Liquid

The matter which has no fixed shape but has a fixed
volume is called liquid. Water, milk, ink, cooking oil,
kerosene, petrol, diesel, alcohol, etc. are some
examples of liquids. The liquids have the following Milk in glass Water in river
characteristics.
Figure 11.2: Some liquids

opaque /əʊˈpeɪk/ - not clear enough to see through or allow light through

CHEMISTRY Oasis School Science and Environment - 7 115

(i) Liquids do not have a fixed shape. They take the shape of their container.
(ii) Liquids have a fixed volume.
(iii) Liquids flow easily because their molecules are loosely packed.
(iv) Liquids cannot be compressed much.

Gas

The matter which has neither a fixed shape nor a
fixed volume is called a gas. Air, oxygen, carbon
dioxide, nitrogen, hydrogen, carbon, neon, argon,
water vapour, etc. are some examples of gases.
The gases have the following characteristics.

(i) Gases do not have a fixed shape because Figure 11.3: Gases are filled in
the position of their molecules are not balloons and cylinders
fixed.

(ii) Gases do not have a fixed volume.

(iii) Gases flow very easily.

(iv) Gases can be compressed very easily because the molecules in gas are far
apart from each other.

11.3 Elements

We use different types of elements in our daily life, e.g. gold (Au), iron (Fe), copper
(Cu), silver (Ag), etc. They are pure substances. An element is a pure substance
which is made of only one kind of atoms. For example, iron is an element because
it is made of only one type of atoms. Similarly, copper is also called an element as it
is made of only one kind of atoms.

All the atoms of an element are identical but the atoms of different elements are
different. Since an element is made of only one kind of atoms, it cannot be split
into two or more simpler substances. So, an element can also be defined as the
pure substance which cannot be split up into two or more simpler substances by
ordinary chemical methods. Elements themselves are the simplest substances. So
they cannot be split up into any more simpler substances.

Cu Cu Cu Cu Cu

Cu Cu Cu Cu Cu Only copper atoms
Cu Cu Cu Cu Cu

Cu Cu Cu Cu Cu

Fig 11.4: Copper is an element. It is made of only copper atoms



116 Oasis School Science and Environment - 7 CHEMISTRY

Some common examples of elements are hydrogen, helium, oxygen, nitrogen,
sodium, magnesium, gold, copper, iron, silver, carbon, etc. A total of 118 elements
are known so far. Out of these, 92 elements occur naturally on the earth and
remaining 26 elements have been prepared artificially by scientists.

At the room temperature, elements exist in solid, liquid and gaseous states. Elements
like iron, copper, silver, gold, etc. are found in solid state. Elements like bromine,
mercury, caesium, gallium, etc. are found in liquid state. Similarly, elements like
hydrogen, oxygen, nitrogen, neon, helium, etc. are found in gaseous state.

11.4 Symbol

In order to write chemical reactions quickly and conveniently, each element is
represented by one or two letters of its name, which is called symbol. A symbol is
the short way to write an element. The symbol of an element is the first letter or the
first letter and another letter of the English name or Latin name of that element.

Generally, the first letter of the name of an element is written as the symbol of that
element. There are, however, some elements whose names begin with the same
letter. In such cases, one of the elements is given a one-letter symbol but all other
elements are given two letter symbol. For example, the names of elements Carbon,
Chlorine, Calcium, Chromium and Cobalt, all begin with the same letter ‘C’. So, only
carbon is given a one-letter symbol, i.e. C whereas Chlorine, Calcium, Chromium
and Cobalt are given two letter symbol, i.e. Cl, Ca, Cr, and Co respectively. Please
note that in a two-letter symbol, the first letter is written as a capital letter and the
second letter as a small letter.

The symbols of first twenty elements derived from their English or Latin name are
given below:

Atomic number Names of elements Symbols

1. Hydrogen H

2. Helium He
3. Lithium Li
4. Beryllium Be
5. Boron B
6. Carbon C
7. Nitrogen N
8. Oxygen O

9. Fluorine F

10. Neon Ne

11. Sodium (Natrium) Na

12. Magnesium Mg

CHEMISTRY Oasis School Science and Environment - 7 117

13. Aluminium Al
14. Silicon Si
15. Phosphorus P
16. Sulphur S
17. Chlorine Cl
18. Argon Ar
19. Potassium (Kalium) K
20. Calcium Ca

In the above table, the symbols of most of the elements have been derived from
the letters of their English names but the symbols of Sodium and Potassium have
been derived from their Latin names. The symbol of Sodium, i.e. ‘Na’ has been
derived from its Latin name Natrium. Similarly, the symbol of Potassium, i.e. ‘K’
has been derived from its Latin name Kalium. The symbol of an element represents
two things, viz. name of the element and one atom of that element.

11.5 Compound

When two or more atoms of different elements combine together, a new substance is
formed which is called a compound. In a compound, the atoms of different elements
combine in a fixed proportion by weight. So, a compound is a substance made up
of two or more atoms of different elements in a fixed proportion by weight. Water
(cHom2Op)o, ucnardbso. n dioxide (CO2), sodium chloride (NaCl), etc. are some examples of

(oWCf a)o taxenyr dg(He tnw2O (oO) a)its. o Cama crsob omofn po odxuyiongxdeind m e(O a(Cd).eO S u2i)mp i siol aaf rtclwoy,mo s poadtoouimunmsd omcfh a lhodyreid durepo ( goNefn ao Cn(Hle) )ai sta onam dco oomnf cepa oarutbonomdn
made up of one atom of sodium (Na) and one atom of chlorine (Cl).

HH OC O Na Cl
O

Water (H2O) Carbondioxide Sodium
Fig. 11.5: Some compounds (CO2) chloride (NaCl)

Compounds are formed as a result of chemical reaction between any two or more
elements. Therefore, compounds do not contain the properties of elements.

proportion /prəˈpɔːʃ(ə)n/ - a part or share of a whole CHEMISTRY
118 Oasis School Science and Environment - 7

Differences between Elements and Compounds

Elements Compound

1. An element is made up of only one 1. A compound is made up of two
type of atom. or more types of atoms.

2. An element cannot be split into 2. A compound can be split into
simpler substances having different simpler substances having
properties. different properties.

3. The smallest particle of an element is 3. The smallest particle of a
called atom. compound is called a molecule.
Examples: Hydrogen (H), Oxygen d(ENixoaaxmCidlp)e,l ee(stCc: O.W2a),t eSro (dHiu2Om) ,c Chlaorrbiodne
(O), Carbon (C), Copper (Cu), Gold
(Au), etc.

11.6 Atom – Shell or orbit

Elements are made of tiny particles. These tiny particles + Nucleus
are called atoms. An atom is the smallest particle of + Proton
an element which can take part in a chemical reaction. – Neutron
All the atoms of an element are same but the atoms Electron
of different elements are different. For example, all
the atoms of hydrogen are similar but the atoms of Fig. 11.6: A neutral atom
hydrogen differ from the atoms of silver or sodium or
copper. The atoms of all 118 elements differ from each other. Atoms may or may
not exist freely in nature. For example, atoms of helium, neon, argon, etc. can exist
freely in nature but atoms of hydrogen, sodium, oxygen, etc. cannot exist freely in
nature.

An atom is made of three fundamental particles: proton, neutron and electron.
These fundamental particles are called sub-atomic particles. Proton and neutron are
located in the nucleus of an atom whereas electrons revolve around the nucleus in
elliptical orbits called shells. Protons are positively charged, neutrons are chargeless
and electrons are negatively charged sub-atomic particles.

11.7 Molecule

A molecule is the smallest particle of an HH OO
element or a compound which can exist

freely. The molecule of an element consists A hydrogen molecule An oxygen molecule
of two or more atoms of the same kind. For Fig 11.7

example, a molecule of hydrogen element

((HO22)) ccoonnssiissttss ooff twtwoo a atotomms so of fo xhyygderno.g en. Similarly, a molecule of oxygen element

CHEMISTRY Oasis School Science and Environment - 7 119

The molecule of a compound consists of HOH
two or more atoms of different elements.
For example, a molecule of sodium Na Cl

chloride contains one atom of sodium A molecule of sodium chloride A molecule of water
(Na) and one atom of chlorine (Cl).
Fig 11. 8
Scoimntialainrlsy ,t wao amtoomlesc uolfe h yodf rowgaetne r( H()H a2nOd) one atom of oxygen (O).

11.8 Molecular Formula

The molecule of a substance is represented by writing its chemical formula. A
chemical formula represents the composition of a molecule of a substance in terms
of the symbols. So, the symbolic representation of the molecule of a substance is
called molecular formula. For example, the molecular formula of sodium chloride
(common salt) is NaCl.

The molecular formulae of some common elements and compounds are given below:

Elements Molecular Compounds Molecular
formulae formulae

1. Hydrogen H2 1. Water H2O
2. Oxygen O2 2. Carbon dioxide CO2
3. Nitrogen N2 3. Sodium chloride NaCl
4. Chlorine Cl2 4. Hydrogen chloride
5. Bromine Br2 5. Calcium oxide HCl

CaO

In order to write the molecular formula of C + O2 CO2
an element or a compound, we first write
the symbol of the elements. The number of
atoms in the molecule is then written as a OC O

subscript just after the symbol of the atoms.
For example, carbon dioxide is a compound. Fig 11. 9: A molecule of carbon dioxide (CO2 )
It consists of one atom of carbon (C) and
wtwhoic aht oism csl eoafr loyx yshgoewn n(O in). tShoe, gthive emn ofilgecuurela. r formula of carbon dioxide will be CO2

The molecular formula provides a short-hand way of writing a compound. The
molecular formula tells us the names of elements and number of their atoms present
in one molecule of a compound.

11.9 Change in Matter

When water is heated, it changes into vapour and when the vapour is cooled, it
again changes into water. It is a temporary change. But when a piece of paper is
burnt, it changes into ash and gas. This change is a permanent change. On this
basis, change in matter occurs in two ways: physical change and chemical change.

120 Oasis School Science and Environment - 7 CHEMISTRY

a. Physical change

Physical change is the temporary change in which only physical properties (like
shape, size, colour, etc.) are changed. The chemical properties of the substance
remain unchanged. Conversion of water into ice, conversion of water into water
vapour, melting of ice, tearing a piece of paper, etc. are some examples of physical change.
Characteristics of physical change
(i) Physical change is a temporary and reversible change.
(ii) New types of substances are not formed in a physical change.
(iii) In a physical change, chemical properties of the substance remain unchanged.

b. Chemical change

Chemical change is a permanent change in which new type of substances are
formed. It takes place due to chemical reaction between any two or more substances.
Burning of a piece of paper, rusting of iron, formation of curd from milk, etc. are
some examples of chemical change.
Characteristics of chemical change
(i) Chemical change is a permanent and irreversible change.
(ii) New type of substances are formed in a chemical change.
(iii) In a chemical change, physical as well as chemical properties of substances
are changed.
Differences between Physical change and Chemical change

S.N. Physical Change S.N. Chemical change

1. It is a temporary change. 1. It is a permanent change.

2. It is a reversible change. 2. It is an irreversible change.

3. New substances are not formed. 3. New substances are formed.

4. Chemical properties of the 4. Physical as well as chemical
substance do not change. properties of substances are
changed.

Activity 1

• Heat some water in a kettle for a while.
• Can you see water vapour coming out of the kettle?
• Place a cold plate near the water vapour. Does water vapour change into

water?
• What type of change is this? Why?


CHEMISTRY Oasis School Science and Environment - 7 121

Activity 2

• Take a piece of iron or an iron nail. Keep the nail in a moist place for 2- 3 days.
• Observe the nail after 2-3 days. Can you see rust on the outer surface of the nail?
• What type of change is this? Why?



Summary

• Anything which has mass and volume is called matter.
• Matter can exist in three physical states, viz. solid, liquid and gas.
• An element is a pure substance which is made of only one kind of atoms and

cannot be split up into two or more simpler substances by ordinary chemical
methods.
• The symbol of an element is the first letter or the first letter and another letter
of the English name or Latin name of that element.
• A compound is a substance made up of two or more atoms of different
elements in a fixed proportion by weight.
• An atom is the smallest particle of an element which can take part in a
chemical reaction.
• A molecule is the smallest particle of an element or a compound which can
exist freely.
• The molecule of a compound consists of two or more atoms of different
elements.
• The symbolic representation of the molecule of a substance is called molecular
formula.
• Change in matter occurs in two ways, viz. physical change and chemical
change.
• Physical change is the temporary change in which only physical properties
(like shape, size, colour, etc.) are changed.
• Chemical change is a permanent change in which new type of substances are
formed.

122 Oasis School Science and Environment - 7 CHEMISTRY

Exercise

1 Choose the best answer from the given alternatives.

a. The matter having a fixed shape and volume is called ______.

(i) solid (ii) liquid

(iii) gas (iv) fluid

b. The pure substance which cannot be split into simpler substance is
called ______.

(i) compound (ii) element

(iv) molecule (iv) matter

c. The symbol of carbon is ______.

(i) Ca (ii) Co

(iii) C (iv) Cr

d. The molecular formula of carbon dioxide is ______.

(i) Co (ii) CO2

(iii) CO2 (iv) C2O

e. Which of the following is a chemical change?

(i) melting of ice (ii) burning of a paper

(iii) tearing a paper (iv) making a knife from iron

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. The substance which does not have mass and volume is called matter.

b. Liquids and gases flow easily.

c. The symbol of potassium is P.

d. The smallest particle of an element is called atom.

e. Rusting of iron is a physical change.

3 Fill in the blanks with appropriate words.
a. The substance having ..................... and ..................... is called matter.
b. An element is made of similar types of .....................
c. A molecule of water contains ..................... atoms of hydrogen and .....................
atom of .....................
d. The molecular formula of carbon dioxide is .....................
e. ..................... change is a temporary change.

CHEMISTRY Oasis School Science and Environment - 7 123

4 Answer the following questions.
a. What is matter? Give any three examples.
b. What are three states of matter?
c. What are solids? Write any three properties of solids with any two examples.
d. What are liquids and gases? Give any two examples of each.
e. What is an element ? Give any three examples.
f. What is a symbol ? Write with examples.
g. What is a compound? Give any three examples.
h. Define atom and molecule with any two examples of each.
i. What is meant by molecular formula?
j. What is a physical change ? Give any two examples.
k. What is a chemical change? Give any two examples.

5 Differentiate between:
a. Solids and Liquids
b. Liquids and Gases
c. Elements and Compounds
d. Atoms and Molecules
e. Physical change and Chemical change

6 Write down the symbols of the given elements.
a. Sodium b. Sulphur
c. Potassium d. Calcium

7 Write down the molecular formula of the given compounds.
a. Water b. Sodium chloride

c. Carbon dioxide d. Calcium chloride

8 Draw a neat diagram showing
a. a neutral atom.

b. a molecule of water.

c. a molecule of carbon dioxide.

124 Oasis School Science and Environment - 7 CHEMISTRY

Unit Estimated teaching periods: Th Pr
9 2
12

Centrifuge machine

Mixture

Objectives

After completing the study of this unit, students will be able to :

• explain and demonstrate some methods of separating the components of
mixture (evaporation, sublimation, centrifuging and crystallization).

• describe the utilities of mixture.
• define solution and differentiate between dilute and concentrated solution.
• introduce unsaturated, saturated and supersaturated solution and demonstrate

them.
• explain the utilities of solution in our daily life.

Course of Study

• Methods of separating components of mixture (Evaporation, Sublimation,
Centrifuging, Crystallization)

• Uses of mixture
• Solution, dilute solution and concentrated solution
• Unsaturated, saturated and supersaturated solution
• Utilities of solution in our daily life

Points to be Focused / Questions to be Discussed

• What are various methods of separating mixtures?
• What types of mixtures can be separated by evaporation, sublimation,

centrifuging and crystallization?
• What is a solution? What are its types?
• What are unsaturated, saturated and supersaturated solution?
• What are the uses of mixture and solution?

CHEMISTRY Oasis School Science and Environment - 7 125

12.1 Introduction

We use a variety of things in our day to day life. Among them, most of the things
are mixtures. Some of the mixtures around us are air, soil, tap water, milk, tea,
coffee, biogas, soft drinks, juice, etc. For example, air is the mixture of various gases
like oxygen, nitrogen, carbon dioxide, water vapour, etc. Soil is the mixture of sand,
clay, salts and remains of living beings. Similarly, tea is the mixture of water, milk,
sugar and tea-leaves. When two or more substances are brought together in any
proportion, the resulting mass is called mixture.

A mixture is made up of two or more different kinds of substances. The substances
which are present in a mixture are called components of the mixture. The
components of a mixture retain their original properties. So, a mixture shows the
properties of all the substances present in it.

The state of a mixture may be solid, liquid or gas. Similarly, a mixture may contain
solid and liquid or liquid and gas. Some forms of mixture are as follows:
(i) Mixture of solid and solid
Examples: Sand and camphor, salt and sand, rice and bran, etc.
(ii) Mixture of solid and liquid
Examples: Salt and water, sugar and water, sugar and milk, etc.
(iii) Mixture of liquid and gas
Examples: Coca-cola, sprite, beer, etc.
(iv) Mixture of gas and gas
Examples: Oxygen and nitrogen, air and smoke, air and water vapour, etc.

In some of the mixtures, we can easily see the components of the mixture but in
some other cases we cannot see all the components of the mixture. For example,
in the mixture of sugar and sand, we can see both components of the mixture but
in the mixtures like tea, juice, and milk, we cannot see all the components of the
mixture.

12.2 Reasons for Separating the Components of a Mixture

We make tea by boiling tea-leaves in water adding sugar and milk. Then we
remove the tea-leaves using a sieve (tea-strainer) before drinking it. Used tea-leaves
are undesirable component. When we buy rice, pulses, etc. from the market, these
things contain pieces of stone, insects and other harmful substances. Tap water
may contain some impurities. So, tap water is filtered before drinking. From these
examples, it can be concluded that the mixtures are separated into their components to:
(i) remove undesirable components.
(ii) remove harmful and useless components.
(iii) obtain pure substances.
(iv) obtain useful substances.

126 Oasis School Science and Environment - 7 CHEMISTRY

12.3 Methods of Separation of Components of Mixtures

We separate the various mixtures into their components to make them useful in
our day to day life. The different components of a mixture have different physical
properties such as solubility, density, size, etc. These differences in physical
properties are utilized to separate them from a mixture. Therefore, we should first
know the physical properties of the components of a mixture in order to select
suitable method for separating the components of a mixture. Different methods are
used to separate the components of different mixtures. In this unit, we will discuss
only four methods. They are (i) Evaporation (ii) Sublimation (iii) Centrifugation
and (iv) Crystallization.

(i) Evaporation

When water is heated, it changes into Steam
vapour or gaseous state. This process
is called evaporation. So, the changing Evaporating dish
of a liquid into vapours or gas is called
evaporation. Copper sulphate
solution

Evaporation is used to separate the
components from the homogeneous
mixture of solid and liquid. The dissolved Stand

substance is left as a residue when all the
water or liquid is evaporated. The use of
the process evaporation is based on the
fact that liquids change easily into vapour
on heating whereas solids do not change
into vapour easily. The evaporation of a
liquid at room temperature is very slow. Fig. 12.1: Evaporation of water

So, it can be made quicker by heating the solution.

Water evaporates

Porcelain basin Solution of salt
Wire gauze and water

Stand
Bunsen burner

(a) (b)

Fig. 12.2: Evaporation

CHEMISTRY Oasis School Science and Environment - 7 127

The common salt dissolved in water can



be separated by evaporation. First of all,
the solution of common salt and water is
taken in a porcelain basin or a beaker. Then
the solution is heated gently as shown in
the fig. 12.2 (a). The water present in the
solution changes into vapour on heating Figure 12.3: Separation of salt from sea water
and escapes into atmosphere. When all the
water present in the solution gets evaporated, the common salt is left behind in the
porcelain basin as shown the fig. 12.2 (b).

By evaporation, we can separate salt, sugar, copper sulphate, potassium nitrate,
alum, etc. from their solutions in water. The process of evaporation is used on a
large scale to separate common salt from sea-water. The sea-water is trapped in
shallow lakes and allowed to remain there.

The heat of the sun gradually evaporates the water present there and common salt
is left behind as a solid. In this way, salt is obtained from the sea water.

Activity 1

• Make a concentrated solution of common salt and water in a porcelain
basin.

• Heat the solution gently till all water gets evaporated. What is left behind
on the porcelain basin?

• What is this method of separation of mixture called?


(ii) Sublimation

Most of the solid substances, when heated, first change into liquid and then
into vapours or gaseous state. But some solid substances like camphor, iodine,
naphthalene, ammonium chloride, etc. change directly into vapours on heating.
These substances are called sublimes. These substances change directly into
vapours on heating and the vapours change into solid on cooling. So, the changing
of a solid directly into vapours on heating and of vapours into solid on cooling is
called sublimation.

Solid (Sublime) Heating Vapours or gas
Cooling

The solid substances that undergo sublimation are called sublimes.
But most of the solid substances are not sublimes. So, sublimation process is
used to separate the sublime from the mixture of sublime and non-sublimes.
Substances like camphor, iodine, naphthalene, ammonium chloride, etc. are
separated from a mixture by sublimation. For example, the mixture of camphor
and common salt can be separated by sublimation because camphor sublimes on
heating but common salt does not.

sublime /səˈblaɪm/ - solid that can be changed directly into vapour on heating

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Experiment 1

Objective: To separate a mixture of common salt and camphor by sublimation
process

Materials required

Camphor, common salt, porcelain basin (China dish), wire gauze, glass funnel,
tripod stand, Bunsen burner, match box, moist cotton

Procedure

• Take a porcelain basin (China dish) Cotton plug
and keep the mixture of camphor and Camphor vapours Inverted funnel
common salt in it.
Camphor solidified

• Place the porcelain basin on the wire China dish
gauze kept on a tripod stand.

• Cover the porcelain basin with an Burner
inverted glass funnel.

• Put a loose cotton plug in the upper Figure: 12.4: Sublimation
open end of the funnel and cover the
outer surface of the funnel with moist cotton.

• Now, heat the mixture gently by using a burner.

Observation

When the mixture of camphor and common salt is heated, camphor changes into
vapours but common salt does not. The vapours of camphor get converted into
solid camphor when it comes in contact with cold inner walls of the glass funnel.
In this way, pure camphor can be separated from the mixture of common salt and
camphor.

Conclusion

The mixture of camphor and common salt can be separated by sublimation.

(iii) Centrifugation

The mixture of heavy particles and
light particles can be separated into its
components by rotating the mixture at a
very high speed. This process of separating
mixture is called centrifugation. Thus,
centrifugation is the method of separating
the mixture of heavy particles and light
particles or suspended particles of a
substance by rotating the mixture at very
high speed. Centrifugation is done by
using a machine called centrifuge.

Figure: 12.5 (a): Centrifuge machines

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In centrifugation, the mixture of suspended particles in a liquid is taken in test
tubes. The test tubes are placed in a centrifuge machine and rotated rapidly for
a while. As the mixture rotates round rapidly, heavier suspended particles settle
down at the bottom of the test tubes and the lighter particles or liquid remains
on top. Then the mixture can be separated by decantation. We can separate clay
particles suspended in water, cream from milk, chalk powder from water, sand and
water, blood cells from plasma, etc. by centrifugation.

When the mixture of heavy particles and light particles rotates round rapidly, more
force acts on heavy particles than that in light particles. As a result, heavier particles
are settled at the bottom of the container.

Activity 2

• Take a beaker and prepare a mixture of sand and water.
• Place the mixture in a plastic bottle.
• Tie the neck of the bottle firmly with a strong string and rotate it gently for

a while. [Be aware of accidents.]
• Observe the bottle. Does the sand settle at the bottom of the bottle?
• Write down the conclusion of this activity.


Experiment 2

Objective: To separate the mixture of chalk–powder and water by centrifugation
Materials required: Mixture of chalk powder and water, test tubes, centrifuge
Procedure
• Take a mixture of chalk-powder and water and keep it in four test tubes.
• Put these test tubes in a centrifuge machine and close the mouth of the

centrifuge with the lid.
• Now, switch on the centrifuge machine to rotate the mixture for a while.
• Switch off the centrifuge and observe the mixture in the test tubes.
What do you observe? Does the chalk-powder settle at the bottom?
Observation
After rotating the mixture in a centrifuge, the chalk-powder settles at the bottom
and water remains over the chalk-powder.
Conclusion
The mixture of chalk-powder and water can be separated by centrifugation.

decant /dɪˈkænt/ - to pour liquid from one container to another

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(iv) Crystallization Glass rod

When a hot and highly Solution Porcelain basin
of copper
concentrated solution of a solid is sulphate and
cooled, crystals of the substance water
are formed. This process Wire gauze

of getting crystals is called Tripod stand
crystallization. The process of Bunsen burner
getting solid crystals by cooling
a hot concentrated solution of a
substance is called crystallization. Figure 12.6: Crystallization

This process is used to get pure crystals of a solid substance from its solution.
Crystals are pure solid substances having a fixed geometrical shape, smooth
surfaces and sharp edges. They do not contain any impurities.

Copper sulphate Common salt Sugar

Fig.. 12.7: Crystals of some substances

Crystallization is also used to purify an impure solid substance in the form of
crystals. It is done as follows:

Step 1
The impure solid substance is taken and dissolved in hot water as much as possible
in order to get a highly concentrated solution.

Step 2
The hot concentrated solution is filtered to remove insoluble impurities.

Step 3
The filtered concentrated solution is allowed to cool gradually for a few days

without disturbing it. On cooling for a few days, pure crystals of the substance can
be obtained.

Step 4
The crystals are separated from the solution by filtration.

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We can obtain big crystals by cooling the hot concentrated solution for many days
without disturbance. Similarly, we can suspend a small seed-like crystal of that
substance in the solution with a thread in order to get big crystals.

Experiment 3

Objective: To prepare the crystals of copper sulphate
Materials required: Copper sulphate, porcelain basin, water, glass rod, wire gauze,
tripod stand, Bunsen burner, match box
Procedure
• Take a porcelain basin and boil some water in it.
• Dissolve some copper sulphate in it and stir it with a glass rod.
• Dissolve as much copper sulphate as possible to prepare a highly concentrated

solution.
• Now, remove the solution from the flame and leave it undisturbed for cooling.
• Observe the solution after 2 – 3 days. What do you observe?

Solution Glass rod Glass rod
of copper Porcelain basin Thread
sulphate and
water

Wire gauze

Tripod stand Beaker
Bunsen burner Small crystal

(a) (b)

Fig. 12.8: Crystallization

Observation
Crystals of copper sulphate can be seen in the basin after 2 – 3 days.

Conclusion
In this way, crystals of copper sulphate can be obtained by crystallization.

Activity 3

• Take some sugar or alum and make its highly concentrated solution by
dissolving it in hot water.

• Remove the solution from the flame and suspend a thread into the solution.
• Cool the solution at room temperature and observe the crystals after 2 – 3

days.


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12.4 Uses of Mixture

We use various substances in the form of mixture. The common uses of mixture are
given below:
(i) Plants absorb various minerals and salts in the form of mixture.
(ii) We use mixture of cement, sand, water, etc. in construction works.
(iii) Mixture of various chemicals is used to prepare medicines.
(iv) We take our food in the form of mixture.
(v) Mixture of various colours is used in painting.

12.5 Solution

Take some water in a beaker and add a spoon of sugar in it. Stir it with a spoon.
Sugar dissolves in water. It is called sugar solution. A solution is the homogeneous
mixture of two or more substances. For example, solution of sugar and water,
solution of salt and water, etc. We cannot see all the components of a solution.

Spoon

Stirring

Sugar Sugar solution
Beaker

Water

Fig. 12.9: Sugar solution
A solution consists of solvent and solute. So, an intimate mixture of a solute and

solvent is called a solution.

Solution = Solute + Solvent

The substance in which a solute dissolves is called a solvent. For example, water,

alcohol, ether, etc. The substance which dissolves in a solvent is called a solute. For
example, common salt, sugar, copper sulphate, etc. In the solution of common salt
and water, salt is a solute and water is a solvent. Similarly, in the solution of copper
sulphate and water, copper sulphate is a solute and water is a solvent.

12.6 Dilute Solution and Concentrated Solution

Between any two solutions, the quantity of a solute may be relatively more or less.
The solution having relatively less amount of solute is called dilute solution and the
solution having relatively more amount of solute is called concentrated solution.
The concentration of a solution depends on the amount of a solute dissolved in a
fixed volume of a solvent.



CHEMISTRY Oasis School Science and Environment - 7 133

Activity 4

• Take two beakers and mark them 'A' and 'B' with a marker.
• Keep 50 ml of water in each of the beakers.
• Add two drops of ink in beaker 'A' and six drops of ink in beaker 'B'. What

do you observe?
• Which solution ('A' or 'B') appears dark? Why?
• Which solution is dilute and which is concentrated? Why?
• Write down the conclusion of this activity.

Activity 5

• Take two glasses and fill them with drinking water.
• Mark them 'A' and 'B' with a marker.
• Add one spoonful sugar in glass 'A' and stir it.
• Add three spoonful of sugar in glass 'B' and stir it.
• Now, taste one spoonfull of sugar solution from both beakers one by one.
• What do you feel? Which solution (A or B) is sweeter? Which one is dilute

solution and which one is concentrated solution ? Why ?
• Write down the conclusion of this activity.


12.7 Unsaturated, Saturated and Supersaturated Solution

The solution in which some more solute can be dissolved at a given temperature is
called unsaturated solution. The solution in which no more solute can be dissolved at
a given temperature is called saturated solution. A saturated solution at a particular
temperature becomes unsaturated when the temperature is increased and we can
dissolve more solute in it at higher temperature. This solution discharges excess
solute as solid when it is cooled. Such a solution is called supersaturated solution.
So, the saturated solution prepared at a higher temperature which throws excess
solute as solid when cooled is called supersaturated solution.

12.8 Method for Identifying Unsaturated, Saturated and
Supersaturated Solution

The type of a solution of a solute can be identified by using some crystals of that
solute. When a crystal of the given solute dissolves in a solution, the solution is
unsaturated. If the crystal does not dissolve in the solution at a certain temperature,
the solution is saturated. If the crystal does not dissolve and its size increases
gradually, then the type of the solution is supersaturated.

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12.9 Uses of Solution in Our Daily Life

Glass rod

Beaker More solute Crystal becomes
does not larger but does not
More solution dissolve dissolve
dissolves

Unsaturated solution Saturated solution Supersaturated solution

Fig. 12.10: Different types of solution

1. Plants absorb salt and minerals in the form of solution.
2. The food that we take is digested and absorbed in the form of solution.
3. Aquatic plants and animals inhale oxygen in the form of water solution.
4. Most of the medicines, paints, ink, etc. are prepared and used in the form of solution.
5. We use some drinks in the form of solution.

TT Summary
•
When two or more substances are brought together in any proportion, the
• resulting mass is called mixture.
The substances which are present in a mixture are called components of the
• mixture.
We separate the various mixtures into their components to make them
• useful in our day to day life.
• The changing of a liquid into vapours or gas is called evaporation.
The changing of a solid directly into vapours on heating and of vapours into
• solid on cooling is called sublimation.
Centrifugation is the method of separating the mixture of heavy particles
• and light particles or suspended particles of a substance by rotating the
mixture at very high speed.
• The process of getting solid crystals by cooling a hot concentrated solution
of a substance is called crystallization.
• Crystals are pure solid substances having a fixed geometrical shape, smooth
• surfaces and sharp edges.
• A solution is the homogeneous mixture of two or more substances.
• The substance in which a solute dissolves is called a solvent.
The substance which dissolves in a solvent is called a solute.
• The solution having relatively less amount of solute is called dilute
solution and the solution having relatively more amount of solute is called
concentrated solution.
The saturated solution prepared at a higher temperature which throws
excess solute as solid when cooled is called supersaturated solution.

CHEMISTRY Oasis School Science and Environment - 7 135

Exercise

1 Choose the best answer from the given alternatives.

a. When two or more substances are brought together, the resulting mass is
called ______.

(i) solution (ii) mixture

(iii) solute (iv) solvent

b. The mixture of sand and camphor can be separated by ______.

(i) crystallization (ii) sublimation

(iii) evaporation (iv) centrifugation

c. The mixture of salt and water can be separated by ______.

(i) evaporation (ii) sublimation

(iii) crystallization (iv) sedimentation

d. The method of separating mixture by rotating the mixture at a high speed is
called ______.

(i) centrifugation (ii) crystallization

(iii) evaporation (iv) sublimation

e. The solution that cannot dissolve any more solute at a given temperature is
called ______.

(i) dilute solution (ii) saturated solution

(iii) unsaturated solution (iv) supersaturated solution

2 Tick (√) the correct statement and cross (×) the incorrect one.

a. The mixture of sugar and water can be separated by evaporation.

b. Camphor and iodine are sublimes.

c. Centrifuge machine is used for crystallization.

d. Solution is the homogeneous mixture of solution and solvent.

e. Unsaturated solution cannot dissolve any more amount of solute.
3 Fill in the blanks using appropriate words.

a. The mixture of iodine and sand can be separated by .................................
b. ................................. method is used to obtain pure crystals of common salt.
c. Cream is separated from milk by .................................
d. A solution consists of ................................. and ...............................
e. The saturated solution prepared at a high temperature is called ............................

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4 Answer the following questions.
a. What is a mixture? Why are the components of a mixture separated? Give
any three reasons.
b. What is evaporation? What type of mixture can be separated by this method?
c. What is sublimation? Name any two sublimes.
d. What is centrifugation? What type of mixture can be separated by this
method?
e. What is crystallization? Define crystals.
f. What is a solution? Give any two examples.
g. Define solute and solvent with any two examples of each.
h. What do you mean by dilute and concentrated solution?
i. What is an unsaturated solution?
j. What are saturated and supersaturated solution?
k. Write down any four uses of solution.

5 Differentiate between:
a. Crystallization and Sublimation
b. Dilute solution and Concentrated solution
c. Solute and Solvent
d. Unsaturated and Saturated solution
e. Unsaturated and Supersaturated solution

6 Write down the suitable method for separating each of the given mixtures.
a. Mixture of sand and ammonium chloride
b. Mixture of sugar and water
c. Mixture of copper sulphate and water
d. Cream and milk
e. Clay and water

7 Describe an experiment to separate the mixture of sugar and water.

8 Describe an experiment to obtain pure crystals of copper sulphate from its
solution.

9 Describe an experiment to obtain pure common salt from the impure rock salt.

10 Write any four uses of mixture in our daily life.

11 How can you identify whether a given solution is unsaturated, saturated or
supersaturated? Describe in brief.

CHEMISTRY Oasis School Science and Environment - 7 137

Unit Estimated teaching periods: Th Pr
9 2
13
Gold

Metal and Non-metal

Objectives

After completing the study of this unit, students will be able to :

• introduce metals and non-metals and differentiate between them.
• define alloys with examples.
• explain the properties and uses of some useful alloys (brass, bronze) and

non-metals (sulphur and iodine).

Course of Study

• Metal and properties of metals
• Non-metal and properties of non-metals
• Alloys and their properties
• Some useful alloys (brass and bronze)
• Some useful non-metals (sulphur and iodine)

Points to be Focused / Questions to be Discussed

• What are metals? What are their properties ?
• What are non-metals? What are their properties?
• What are alloys? Why are they useful?
• What are the properties of brass, bronze, sulphur and iodine?
• What are the uses of brass, bronze, sulphur and iodine?

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13.1 Introduction

A variety of substances are found in our surroundings. Among them, some are
pure and others are impure. The pure substances are called elements. Scientists
have discovered 118 elements so far. On the basis of their properties, elements are
divided into three types. They are metals, non-metals and metalloids. Most of the
elements are hard, malleable, ductile and good conductors of heat and electricity.
These elements are called metals. For example, copper, silver, gold, aluminium,
iron, etc. Some elements are soft, non-malleable, non-ductile and bad conductors
of heat and electricity. These elements are called non-metals. For example, carbon,
sulphur, chlorine, oxygen, nitrogen, iodine, phosphorus, etc. However, some other
elements show the properties of both metals and non-metals. These elements are
called metalloids. For example, silicon, germanium, arsenic, etc.

13.2 Metals

Metals are the solid substances which are malleable, ductile and good conductors
of heat and electricity. They are lustrous substances and produce tinkling sound on
hitting. For example, copper, iron, aluminium, silver, gold, etc. Most of the metals
exist in solid state at the room temperature but mercury exists in liquid state.
Metals are widely used for making various objects of our daily use. Metals like iron,
aluminium and copper are used for making cooking utensils. Gold and silver are
used for making jewellery. Copper and aluminium are also used for making electric
wires. Iron is also used in construction works, for making vehicles, weapons, etc.

Figure 13.1: Metals are used for making different things

13.3 Properties of Metals

(i) Most of the metals are hard.
(ii) Metals are lustrous (shiny).
(iii) Most of the metals are malleable. It means that they can be beaten into thin

sheets and can be folded.
(iv) Most of the metals are ductile. It means that they can be drawn into wires.
(v) Metals are good conductors of heat and electricity.
(vi) Metals produce tinkling sound on hitting.

malleable /ˈmælɪəbl/ - that can be hit or pressed into different shapes easily without breaking or
ductile / ˈdʌktaɪl / cracking

- that can be made into a thin wire

CHEMISTRY Oasis School Science and Environment - 7 139

13.4 Non-metals

Non-metals are generally soft, non-malleable and non-ductile substances that can
be found in solid, liquid or gaseous state. Non-metals are bad conductors of heat
and electricity except graphite. Non-metals are also widely used in our day to day
activities. They are used to make medicines, utensils, containers, etc. They are also
used in construction works. For example, carbon, sulphur, phosphorus, iodine,
chlorine, etc.

13.5 Properties of Non-Metals

(i) Non-metals are found in solid, liquid and gaseous state.
(ii) They are generally soft.
(iii) They are non-malleable.
(iv) They are non-ductile.
(v) They are bad conductors of heat and electricity.
(vi) They are non-lustrous.
(vii) They do not produce tinkling sound on hitting.

Differences between Metals and Non-metals

S.N. Metals S.N. Non-metals

1. Metals are malleable. 1. Non-metals are non-malleable.

2. Metals are ductile. 2. Non-metals are non-ductile.

3. Metals are good conductors of 3. Non-metals are poor conductors
heat and electricity. of heat and electricity.

4. Metals are lustrous. 4. Non-metals are non-lustrous.

5. They produce tinkling sound 5. They do not produce tinkling
on hitting. sound on hitting.

6. They are generally hard. 6. They are generally soft.

Activity 1

• Observe various substances in your surroundings. Study their properties
and classify them in terms of metals and non-metals.

• Make a list of metals and non-metals after your observation.

Metals Non-metals

(i) (i)

(ii) (ii)

(iii) (iii)


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13.6 Alloys

An alloy is a homogeneous mixture of two or more metals or metals and non-
metals. Alloys are widely used in our daily life. Alloys are prepared by mixing two
or more metals in their molten state and then cooling the product. The common
alloys that we use are given below:

1. Steel (Mixture of iron and carbon)

2. Brass (Mixture of copper and zinc)

3. Bronze (Mixture of copper and tin)

4. Stainless steel (Mixture of iron, chromium and carbon)

Alloys have different properties from the properties of their constituent metals or
non-metals. We make and use alloys in order to:

(i) increase strength and hardness.

(ii) get different colours.

(iii) reduce the melting point.

(iv) make utensils rust–free.

Activity 2

• Prepare a list of alloys that are used in your home.
• Ask your seniors and write down their major uses.


13.7 Some Useful Alloys

1. Brass

Brass is a yellow-coloured alloy. It is the mixture of
copper and zinc. Brass is used for making cooking
utensils as it is malleable and good conductor of
heat. It is used for decoration for its bright gold- Fig. 13.2: Things made of brass
like appearance. It is also used for making door
knobs, locks, gears, bearings, boxes, ornaments, buckles of belts, coins, statues, etc.
as rusting does not occur in brass.

2. Bronze

Bronze is a faint yellow coloured alloy. It is the
mixture of copper and tin. Rusting does not occur in
bronze. This alloy has a low melting point than other
metals. The utensils made of bronze look attractive.
Bronze is used to make household utensils like plates,
pitchers, bells, valves, gears, statues, weapons, coins,
medals, musical instruments, etc.
Fig. 13.3: Things made of bronze

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13.8 Some Useful Non-metals Fig. 13.4: Sulphur powder

1. Sulphur
Sulphur is a useful non-metal. Human beings are

using sulphur from pre-historic time. It is insoluble
in water. Sulphur is used for making gun powder,
fire crackers, matches, etc. It is also used for curing
skin diseases. It is used to make insecticides and
fungicides. It is also used in beauty parlours to give
specific shapes to the hair.

2. Iodine

Iodine is a useful non-metal. It has been used by
human beings from prehistoric time. Our body
also requires some amount of iodine. So, we use
iodized salt in our food. Our thyroid gland swells
and enlarges due to the deficiency of iodine.
This condition is called goitre. Iodine is used as
a disinfectant for external wounds. It is also used in Fig. 13.5: Iodine

photography. It is used for preventing goitre by adding in table salt. It is also used
in iodex. It is used in medical treatment of thyroid cancer. It is used as an antiseptic
to treat minor cuts.

Summary

• On the basis of their properties, elements are divided into three types. They are
metals, non-metals and metalloids.

• Metals are the solid substances which are malleable, ductile and good
conductors of heat and electricity.

• Non-metals are generally soft, non-malleable and non-ductile substances that
can be found in solid, liquid or gaseous state.

• An alloy is a homogeneous mixture of two or more metals or metals and non-
metals.

• Brass is used for making cooking utensils as it is malleable and good conductor
of heat.

• Bronze is a faint yellow coloured alloy. It is the mixture of copper and tin.

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