Class 6 Times Science

(Cooking pots having black and rough surfaces are preferred.
(Water pipes in solar panels are blackened.
(Black and dark colored clothes are preferred in winter season.

Uses of heat
Heat can be used for following activities:

a. For cooking food
We use heat for cooking food. We cook food with the
heat produced by burning fuels like wood, coal, bio-gas,
cooking gas, kerosene, etc. We also cook food by using heat
produced from electricity.

b. For keeping our body warm
We need heat to keep our body warm. Heat is produced inside
our body by the reaction of food with oxygen. We get warmth
from the sun, heater, rewood, etc in the winter season.

c. For running vehicles
Vehicles like car, buses, trucks, aeroplanes, motorcycles, etc
run due to heat. Heat is produced by burning fuels like petrol,
diesel, coal, L.P. gas, etc.

d. For running factories
Heat is required for running machines in factories. Heat is
provided to the machines by the electricity and by burning
fuels like petrol, diesel, etc.

e. For drying clothes and food grains
Heat is used to dry our clothes and food grains. We keep clothes
in the sun after washing. We spread food grains in the sun to
dry them.

Temperature

When you touch cold water, you feel cold. When you touch warm
water, you feel warm. But we cannot say how much warm water is
hotter than the cold water. To say this in numerical value, we need
a quantity. This quantity is temperature. Temperature shows the
degree of hotness or coldness of a substance in numerical value.

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Temperature is dened as the degree of hotness or coldness of a
substance.

Its SI unit is Kelvin (K). It is also measured in degree Celsius (°C) and
degree Fahrenheit (°F). It is measured by thermometer.

The substances having high temperature are hotter than the substances
having low temperature. The substances with high temperature have the
molecules vibrating with high speed whereas the substances with low
temperature have the molecules vibrating with low speed.

Thus, the temperature shows the degree of speed of vibration of molecules
of a substance too.

Differences between heat and temperature

Heat Temperature

1. It is a form of energy which gives the 1. It is the degree of hotness or coldness

sensation of warmth. of a substance.

2. It is measured in the units such as 2. It is measured in Kelvin, degree

Joule or Calorie. Celsius or degree Fahrenheit.

3. It is measured by calorimeter. 3. It is measured by thermometer.

Thermometer

It is a device which is used to measure the temperature of a substance.
It works on the principle that “liquid expands on heating and contracts
on cooling”. It contains a liquid called thermometric liquid. Mercury
or alcohol is used as thermometric liquid in a thermometer.

Thermometer is of two types.
a. Laboratory thermometer
b. Clinical thermometer

Laboratory thermometer

It is a thermometer which is used to measure temperature of substances.

Generally, it is used in laboratory. It generally uses alcohol as the
thermometric substance. It measures the temperature from -10°C to
110°C.

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It consists of a capillary tube with a narrow bore. The capillary tube
is swollen to a bulb at one end and is sealed at the other end. The bulb
is lled with alcohol. There is a cover of glass outside the capillary
tube. The outer cover is graduated in degree from -10°C to 110°C.
When the bulb comes in contact with a body whose temperature is
to be measured, there may be rise or fall of the level of alcohol in the
capillary tube. After sometime, the level of alcohol remains xed.
The level of alcohol gives the temperature of the object.

Clinical thermometer

It is a thermometer which is used to measure temperature of a human body.
A clinical thermometer consists of a capillary tube with a ne bore.
One end of the capillary tube is swelled to a bulb. The bulb is lled
with mercury. Another end of the tube is sealed. There is a narrow
constriction in the capillary tube near the bulb. The capillary tube
is covered by a glass cover. The glass cover is graduated in degrees
from 35° to 42°C or 94°F to 108°F.

When we have to measure temperature of a human body, we keep
the bulb of thermometer in the armpit or mouth. There occurs rise in
the level of mercury and reading is obtained. When the thermometer
is taken out from the body, the temperature decreases. But, the level
of mercury does not return to the bulb due to the constriction present
in the capillary tube. This helps to take correct reading. After its use,
the thermometer is jerked to return the mercury to the bulb.

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Main Points to Remember

1. Heat is a form of energy which brings sensation of warmth.
2. The sun, fuels, electricity, friction, combustion of food, etc are

the sources of heat.
3. Heat can cause

i) rise in temperature.
ii) expansion of an object
iii) change in state of matter
4. Black and rough substances are good absorbers of heat.
5. Heat is used for cooking food, keeping our body warm, running
vehicles, running factories, drying clothes and food grains, etc.
6. The degree of hotness or coldness of an object is called
temperature.
7. A device which measures temperature of a body is thermometer.

Exercise

1. Choose the best alternative in each case:

a. The unit of measuring heat

i. Joule ii. Calorie

iii. Both a and b iv. None of these

b. The main source of heat ii. Electricity
i. Fuels iv. Sun
iii. Food

c. Which of the following is not the effect of heat?
i. Rise in the temperature of a body
ii. Expansion of an object
iii. Preparation of food by plants
iv. Change in the state of matter

d. Which of the following is the SI unit of temperature?

i. Degree Celsius ii. Degree Fahrenheit

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iii. Kelvin iv. All of these

e. A clinical thermometer is calibrated between

i. 35 to 42 C ii. 94 to 108 F

iii. -10 to 110 C iv. Both a and b

2. Copy the correct statements and correct the false statements:

a. Electricity, fuels, the sun, etc are the sources of heat.

b. SI unit of heat is calorie.

c. Heat causes rise in temperature.

d. Heat is produced inside our body due to friction.

e. Black and smooth surface is the good absorber of heat.

f. Petrol, diesel, electricity, etc are used to run vehicles.

3. Answer these questions in very short:
a. What is heat? Mention its unit.
b. What are the various sources of heat?
c. What are the various effects of heat?
d. What is heat absorber? Give some examples.
e. What are the uses of heat?
f. What is temperature? Mention its SI unit.
g. What is thermometer? Mention various types of thermometers.

4. Answer these questions:
a. Why is the sun regarded as the main source of heat?
b. Explain about various sources of heat.
c. Explain an activity which shows that heat changes state the
of matter.
d. Explain an activity which shows that black objects are good
absorbers of heat.
e. Explain the various uses of heat.

5. Give reasons:
a. When we rub our palms, they become warmer.
b. Snow melts when there is sunshine.

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c. Base of cooking pots are black and rough.
d. Our body remains warm even in the cold season.
6. Differentiate between:

i. Heat and temperature
ii. Laboratory thermometer and clinical thermometer
7. Draw a laboratory thermometer and label its important parts.

8. Draw a clinical thermometer and label its importance parts

Project Work

Take a round bottomed ask. Fix a long narrow glass tube inside
the ask. Invert the ask and support in a stand. Dip the open
end of the tube into the water of beaker. Heat the ask by the
candle. What happens?
You can see the air bubbles coming through the glass tube from
the ask. Here, the gas inside the ask expands and comes to the
water.

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Chapter

5 LIGHT
Estimated periods:7

OBJECTIVES
At the end of the lesson, the students will be able to:
Ü explain light as a form of energy;
Ü tell the sources of light;
Ü dene and tell examples of transparent, translucent and opaque

objects;
Ü tell the meaning of transmission of light.

MIND OPENERS
Ü Can you see at dark? If not, why?
Ü What helps you to see the things?
Ü What does the sun provide us? Discuss.

Introduction

We cannot see in the dark. We can see the objects only when the light
from the objects falls on our eyes. Hence, the light helps us see things.
The sun is the main source of light. The light from the sun falls upon
the objects such as book, pen, table, road, building, etc. These objects
then reect the sunlight and make the reected light fall into our
eyes. Then, we see objects. Hence, light is a form of energy that gives
the sensation of vision.

Sources of light

The substances which can emit light are known as sources of light.
The sources of light can be classied as natural sources of light and
articial sources of light.

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Natural sources of light

The things which emit light without the help of human beings are
called natural sources of light. These things emit light naturally.
Some of the natural sources of light are explained below:

The sun

The sun is the main source of light for the earth.
The sun also provides us heat. The life on the
earth is not possible without the sunlight. The
sunlight not only makes the objects visible but
also helps plants prepare their food. The food
prepared by plants supports the whole living
world on the earth.

The light travels very fast. It travels with the speed of 3×108 m/s. It
means that the light travels about 30,00,00,000 metres in one second.
The light from the sun takes about 8 minutes and 20 seconds to reach
the earth.

The moon

The moon is also a natural source of light. It
does not emit light of its own but it reects the
light of the sun and makes it fall on the earth.
Hence, the moon light is not hot.

Star

The stars are just like our sun. Some of the
stars are bigger than the sun. They emit light
of their own. But, the stars twinkle at night
because they are very far away from us.

Firey

Firey or glow-worm is a small ying insect.
It has a glowing substance called luciferin on
its tail. So, it seems glowing at night. The light
from the rey is not hot. It is not sufcient
enough to make the things visible.

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Articial sources of light

The human-made devices which emit light as per our desire are called
articial source of light. Several electrical devices such as lament
lamp, uorescent lamp, torch light, etc are capable of converting
electrical energy into light energy and are regarded as the articial
sources of light. Besides these, candles, tuki, lantern, pala, diyalo,
etc are also articial sources of light.

Candle CFL bulb Filament bulb Lantern Diyo

Luminous and non-luminous objects

The natural sources such as the sun, stars, rey, etc emit light of
their own. Similarly, the articial sources emit light of their own
after they are turned on. Such objects are called luminous objects
because they emit light themselves. Hence, the bodies which emit
light of their own are called luminous bodies.

But the objects like book, table, house, tree, roads, etc do not have
light of their own. They become visible by reecting the light of the
luminous objects. Hence, the objects which do not have light of their
own but become visible by reecting the light of others are called
non-luminous objects. The moon is also a non-luminous body because
it does not have its own light . It shines at night by reecting the
light of the sun.

Transparent, translucent and opaque substances

Activity 5.1

Place a burning candle on a table and try to see it by erecting a book
in front of you. Can you see the candle through the book ?
Now, remove the book and erect a piece of glass. Can you see the
candle through the glass ?

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Again, remove the glass and try to see through the oiled paper. Can
you see the burning candle clearly ?

What differences did you get while observing the burning candle
through different substances ?
Observation: You cannot see the candle through the book, but can
see clearly through the glass. You can see candle partially when
observed through an oiled paper.
Some substances allow light to pass through them easily, some allow
light to pass partially while most of the substances do not allow light
to pass through them.
The substances can be classied into transparent, translucent and
opaque on the basis of transmission of light through them.
The substances which allow light to pass through them easily
are called transparent substances. We can see clearly through
such substances. Ordinary glass, air, water and some plastics are
transparent substances.
The substances through which light can pass partially are called
translucent substances. We cannot see the things clearly but we can
see partially through such objects. Greased paper, waxed paper, some
plastics and ground-glass panes are some examples of translucent
substances.
The substances through which light cannot pass at all are called
opaque substances. We cannot see at all through such substances.
For example, book, wood, metals, stone, muddy water, etc.

Rectilinear propagation of light

Light can travel in different media such as air, water, glass, etc.
If light is traveling along the same medium, it always travels in a
straight line. This phenomenon is known as rectilinear propagation
of light.
Hence, the phenomenon in which the light travels in a straight line
through a same transparent medium is called rectilinear propagation
of light.

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Activity 5.2

To show that light travels in a straight line

Materials required: A short piece of exible rubber or plastic tube,
candle and an opaque cardboard

Procedure
1. Burn a candle and
place it on a table.
2. Take a piece of opaque
cardboard paper and
make a hole on its
middle to pass a rubber
tube through it.
3. Hold the tube straight
and point one end to
the burning candle, a
source of light.
4. Observe the candle
through the hole of the
tube. What will you
observe ?
5. Now, bend the table and observe from the same end of the
table. What will you observe ?

Observation: You can see the burning candle only when the
tube is straight.

Conclusion: Light travels in a straight line.

Activity 5.3

To observe the rectilinear propagation of light

Materials required: Cardboard, cardboard stand, candle and
matchbox
Procedure

1. Take three card board sheets of same shape and size.

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2. Make a hole in each of them at the same height.
3. Erect the boards vertically using holders in such a way that

all the holes are at the same height and in a straight line.
4. Light a candle and place it in front of the card board of one end

so that the burning of candle can be seen through the hole.
5. Adjust eye near the card board of another end and look

through the hole. You can see the burning candle.
6. Move the central cardboard slightly so that its hole is not in

the straight line with the others. What do you observe?

Observation: When the holes of card board are in the same straight
line, the burning of candle can be observed from another end. But if
the central card board is move a little up ward, the burning of candle
cannot be seen.

Conclusion: Light always passes along a straight line. This
phenomenon is called rectilinear propagation of light.

Main Points to Remember

1. Light is a form of energy that gives the sensation of vision.
2. The bodies which emit light of their own are called luminous

bodies.
3. The bodies which do not emit light of their own but become

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by reecting the light of others are called non-luminous bodies.
4. The substances through which light can pass easily are called

transparent substances.
5. The substances through which light passes partially are called

translucent substances.
6. The substances through which light does not pass at all are

called opaque substances.
7. The phenomenon in which light travels in a straight line

through a same transparent medium is called rectilinear
propagation of light.

Exercise

1. Choose the best alternative in each case:

a. What time is taken by the sunlight to reach the earth?

i. 5 min ii. 6 min 30 sec

iii. 8 min 20 sec iv. 3 x 108 sec

b. The tail of a rey glows at night due to a chemical substance
called

i. Lime ii. Luciferin

iii. Lantern iv. Limestone

c. Which of the following is a non-luminous object?

i. Sun ii. Stars

iii. Fire iv. Moon

d. Which of the following is a translucent substance?

i. Glass ii. Water

iii. Air iv. None of these

e. Plastic is ii. Translucent
i. Transparent iv. None of these
iii. Opaque

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2. Answer these questions in very short:
a. What is light ?
b. How does light help us to see?
c. What is the speed of light in air ?
d. Give an example each of cold and natural source of light.
e. Is an oiled sheet of paper transparent or translucent? Give
reasons.

3. Give reasons:
a. The moon is a non-luminous object.
b. The glass is a transparent object.
c. The light from the moon does not provide heat.

4. Differentiate between:
a. Luminous and non-luminous bodies.
b. Transparent and translucent objects.
c. Transparent and opaque objects.

5. Answer these questions in detail:
a. Explain the sources of light in brief.
b. Explain the terms translucent and opaque with examples.
c. What do you mean by luminous bodies ? Give examples.
d. What do you mean by non-luminous bodies ?Give examples.
e. How can you show that the light travels in a straight line ?
f. Explain the rectilinear propagation of light with a diagram.

6. Diagrammatic questions:
a. Name the following diagrams and classify them as luminous
and non-luminous bodies.

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b. Draw the diagrams of any ve articial sources of light.

Project Work

Collect different substances such as water, alcohol, oil, plastic,
glass, clay, bricks, greased paper, book and cardboard-sheet.
Observe whether light passes completely, partially or not at all.
Then classify these substances as transparent, translucent and
opaque substances.

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Chapter

6 SOUND
Estimated periods:4

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü dene sound.
Ü tell some sources of sound.
Ü give simple introduction of wave.
Ü explain propagation of sound through various media.

MIND OPENERS
Ü What happens when you blow whistle?
Ü How do you hear the sound produced from any object?
Ü Can sound travel through water? Can sound travel through

vacuum? Discuss.

Introduction

We hear various types of sounds everyday. We hear sound of vehicles,
animals, human beings, radio, television, musical instruments, etc.
Some sounds are pleasant whereas some others are unpleasant. But,
all types of sounds are produced by the vibration of objects. All sounds
produce sensation of hearing in our ears.
So, sound is a form of energy which produces the sensation of hearing
in ears.

Sources of sound

Any object which produces sound is called a source of sound. Radio,
television, madal, guitar, animals, vehicles, human beings, machines,
etc are sources of sound. All sources produce sound through vibration.
Therefore, any vibrating body is the source of sound.

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Guitar Madal Television Radio

A body can be vibrated by hitting, plucking, blowing, stroking, etc.

Activity 6.1
A vibrating object produces sound

Materials required: A bell, hammer or stick
Procedure

1. Take a bell and hit the bell with
metal stick to produce sound.
2. Touch the bell softly. What do you
feel?
Observation: You can feel vibration of the bell. When you hold it
tightly, the bell stops vibrating and production of sound stops.
Conclusion: Vibrating object produces sound.
If you pluck the strings of musical instruments like guitar or sitar,
you can feel the vibration of strings. You can see the vibration of
wings of mosquitoes when they y.

Sound wave

Take a tuning fork. Strike the prongs of the tuning fork with a rubber
pad. Bring the prongs near your ear. You can hear sound. Touch the
prongs of the tuning fork, you can feel vibrations of the prongs.

Now, again strike the prongs of the tuning fork against rubber pad.
Touch the surface of the water with the vibrating prongs. You can see

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the vibrations in the water also. The water moves forming ripples
from the point where you are touching the water surface. These
ripples make waves.

Tuning fork Waves of water

Waves are produced in air as in water when source of sound vibrates
in air. Molecules of air move in such a way that molecules are tightly
arranged in some regions and loosely arranged in other regions. The
region where molecules are tightly arranged is called compression and
the region where molecules are loosely arranged is called rarefaction.
Compressions and rarefactions make a complete wave. In the form of
wave, sound travels from one place to another.

Sound wave

Sharpness of sound

Sound of guitar is different from sound of madal. Sound of a bird is
different from that of a buffalo. Sound of a small baby is different
from that of an adult person. Sound of guitar, bird and baby is sharp
whereas sound of madal, buffalo and adult is not sharp. Sound
having high pitch is sharp. Thin, small and tight objects produce
sharp sound.

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Activity 6.2
To show the relation between sharpness of sound and length of
vibrating object

Materials required: A scale, a table
Procedure

1. Take a scale and place it on a
table so that more than half
part comes out of the edge of
the table.

2. Press one end of the scale
with one hand and pull the
free end of the scale upward
with another hand and leave
the scale. What will you
observe?

Make the free end shorter and repeat the above activity. What
differences do you nd in the sound of above two cases.

Observation: The sound in the second case is sharper than the rst
case. Repeat the experiment for several times by shortening the free
end of the scale.

Conclusion: Smaller or shorter object produces sharp sound.

Loudness of sound

Take a small drum and hit the drum with a drum stick. Listen to the
sound. Now, take a large drum and hit the drum with a drum stick.
Listen to the sound produced. What differences do you nd in the
sound of two drums?

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Sound produced by smaller drum is soft whereas the sound produced
by larger drum is loud.
Again, take a smaller drum only. Hit the drum softly. Then, hit the
drum with a stick with more force. What differences do you nd in
the sound of two cases? In the rst case, sound is soft whereas the
sound is louder in the second case.
Conclusion: i. Larger object produces louder sound.

ii. The object which is hit with more force produces
louder sound.

Propagation of sound

Sound is produced by a vibrating object. Sound passes from one place
to another in the form of wave which is regarded as sound wave.
Sound waves travel through material medium. The material medium
may be solid, liquid or gas. Sound cannot travel in vacuum.
Travelling or movement of sound from one place to another is called
propagation of sound.

Sound can travel through solid

Sound can travel through solid substance. In space, people speak by
using solid medium.

Activity 6.3
To show that sound travels through a solid

Materials required: A scale, desk, etc.
Procedure

1. Tell one of your friends
to keep his/her head
on one end of a desk
with the ear touching
the desk.

2. Hit the another end of
the desk with a scale
softly.

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3. Ask him whether he could listen the sound or not?

Observation: Your friend can hear the sound produced by the scale.
Here, the sound travelled through the desk (solid medium).

Conclusion: Sound travels through solid.

Sound can travel through liquid

Sound can travel through liquid. Aquatic animals hear the sound
travelled through liquid.

Activity 6.4
To show that sound travels through a liquid

Materials required: Steel plate, bucket, water, etc.
Procedure

1. Take a steel plate and hit the
plate with a metal spoon inside
water. What happens?

Observation: You can hear the sound
of the plate. This shows that the sound
travels through water.

Conclusion: The sound travels through the liquid.

Main Points to Remember

1. Sound is a form of energy which produces the sensation of
hearing.

2. Sound is produced by the vibration of an object.
3. Sound travels from one place to another in the form of wave.
4. Thin and small object produces sharp sound.
5. Larger object produces louder sound.
6. Travelling or movement of sound from one place to another is

called propagation of sound.
7. Sound propagates from one place to another through material

medium.

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Exercise

1. Choose the best alternative in each case:

a. Sound is produced due to

i. Frequency ii. Amplitude

iii. Vibration iv. Oscillation

b. The region where the molecules of medium are tightly packed is
called

i. Rarefaction ii. Compression

iii. Crest iv. Trough

c. Sound cannot travel through

i. Solid ii. Liquid

iii. Gas iv. Vacuum

d. A sharp sound has

i. High pitch ii. Low pitch

iii. High speed iv. Low energy

2. Copy the correct statements and correct the wrong statements:

a. Sound is produced by the vibration of an object.

b. Sound produces sensation of vision.

c. Sharp sound has more pitch.

d. Larger objects produce sharp sound.

e. Sound travels through vacuum.

f. Traveling or movement of sound from one place to another is
called propagation of sound.

3. Answer these questions in very short:
a. What is sound? How is it produced?
b. Mention any four sources of sound.
c. What is sound wave?
d. What is propagation of sound?
e. Can sound propagate in vacuum?

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f. Sound produced from a source becomes fainter as it travels
away from the source. Why?

4. Answer these questions in detail:
a. Explain an activity which shows that production of sound
stops when vibration stops.
b. Describe an activity which shows that larger object produces
louder sound.
c. Describe an activity which shows that sound can travel
through solid.
d. Explain an activity which shows that sound travels in the
form of wave.

Project Work

1. Take 5 cups or glasses of different sizes. Keep them in a line.
Hit them with a small rod one by one. Listen to the sound and
note the loudness and sharpness of the sound.

2. Take a plank of wood and x nails at different distances. Put
rubber bands between the nails. Pluck the rubber band and
note the sharpness of the sound.

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Chapter

7 MAGNET
Estimated periods:5

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü dene natural and articial magnets;
Ü identify the magnetic and non-magnetic substances;
Ü explain the properties and uses of magnets.

MIND OPENERS
Ü Have you ever seen or used a magnet?
Ü Where is a magnet used?
Ü What is a magnet made of? Discuss.

Introduction

A magnet looks like iron but it has a power of attracting iron pieces
toward itself. Ancient people learnt about magnetism from loadstones,
naturally magnetized pieces of iron ore. They are the naturally
created magnets, which attract pieces of iron. The word magnet in
Greek meant “stone from magnesia”, a part of ancient Greece where
loadstones were found. It is claimed that magnets were discovered
and were in use in Greece and China 2500 years ago. The loadstone
(lodestone) is also called magnetite. Ancient Chinese navigators
used magnetite to know the directions, especially during the cloudy
weather.
Magnets have very useful attractive property. Hence, they are being used
extensively in different devices. A magnet is used in radio, transistor,
television, speaker, motor pump, electric generator, etc. A magnet can
be used to collect the pieces of iron spread on the ground. Doctors can
use magnet to remove iron pieces if they enter into our eyes.
Magnets have a special property which is known as magnetic property
or magnetism. A freely suspended magnet always comes to rest

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showing the north-south direction. Hence, a magnet is a substance
which attracts magnetic substances and always comes to rest showing
N-S directions when suspended freely.

Magnetic and non-magnetic substances

We can identify magnetic and non-magnetic substances with the
help of a magnet.

Activity 7.1
To identify the magnetic and non-magnetic substances.

Materials required: A bar magnet and a collection of different
substances.
Procedure

1. Collect the substances such as needle, pin, toothbrush, pen,
pencil, book, copper wire, comb, cork, glass tube, iron nail, coin,
pieces of iron, a steel glass, eraser, spoon, etc.

2. Bring each of the above substances close to the bar magnet
one by one and observe whether they are attracted by the bar
magnet.

Observation: Complete the following table with the help of your

observation.

Substances attracted Substances not attracted
by a magnet by a magnet

Conclusion: A magnet does not attract all the substances. It attracts
only some of the substances.
The substances which are attracted by a magnet are called magnetic
substances. For example, iron, cobalt, nickel, etc are magnetic

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substances. Similarly, the substances which are not attracted by a
magnet are called non-magnetic substances. For example, copper,
gold, aluminium, paper, rubber, wood, plastics, etc are non-magnetic
substances.

Natural and articial magnet

The magnet which is found in nature is called natural magnet. It
does not have a regular shape and size. It has low attracting power.
Loadstone is an example of natural magnet. It was found by a
shepherd named magnus in the place magnesia of Asia minor about
2500 years ago. The loadstone had a amazing property of attracting
iron pieces. The load stone used to come to rest pointing north-south
directions when suspended with a piece of thread. In fact, the load
stone is made of a compound of iron called magnetite.

Now a days, magnets are found in required shape, size and strength.
These magnets are made by human beings and are called articial
magnets. Hence, the man-made magnets which are available in
required shape, size and strength are called articial magnets. Some
common examples of articial magnets are: bar magnet, U-shaped
magnet, horse-shoe shaped magnet, needle shaped magnet, block
magnet, disc-shaped magnet, etc.

Articial magnets can be made from iron, cobalt, nickel, etc.
Sometimes, other metals can also be mixed in the above mentioned
metals. Very powerful magnets can also be made as per the need.
The articial magnets are more useful than the natural magnets due
to the following reasons:

a) They are available in required shape and size.
b) They are available in required strength. An articial magnet

can be made weak, strong or very strong.
c) They are light and can be carried easily.

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Magnetic poles

The two ends of a magnet are called its poles. The two poles of a
magnet are denoted by N(north) and S(south). A magnet has more
power at poles. Each piece of a magnet has two poles and the poles of
a magnet cannot be separated.

Properties of a magnet

The magnets are found in different shapes, sizes and strengths. But
all the magnets possess some common properties. They are:

1. Attractive property

A magnet attracts magnetic substances such as iron, cobalt, nickel,
etc. This property of a magnet is called attractive property.

Activity 7.2
To show that a magnet attracts magnetic substances

Materials required: A bar magnet, iron llings (tiny pieces of iron),
sand, a bowl or plate, etc.

Procedure
1. Take a bowl or a plate and mix some sand and iron lling in it.
2. Move a bar magnet to and fro slowly over the mixture.

Observation: You will see that the iron
llings are attracted by the magnet. The
sand is not attracted.

Conclusion: Iron is a magnetic substance.
So, it is attracted by a magnet. This
experiment shows that a magnet has an
attracting property.

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2. Directional property

When a bar magnet tied to a piece of thread is suspended freely, it
always comes to rest pointing north and south directions. This property
of magnet is called directional property. The end of the magnet which
points towards the north is called north pole whereas the end of the
magnet which points towards the south is called south pole.

Activity 7.3
To show that a freely suspended magnet comes to rest showing
north-south directions.

Materials required: A bar magnet, a rigid support or a stand, a
piece of thread, etc.

Procedure
1. Tie a bar magnet at its middle
with a thread.
2. Suspend the magnet carefully
to make it horizontal. You may
use a stand or a rigid support to
suspend the bar magnet.
3. Allow the bar magnet to move
freely and come to rest by its
own. When it comes to rest,
note the directions pointed by it
and push it at one end so that it
moves. Let the magnet come to
rest again. Repeat this process
2-3 times.

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Observation: You will see that the magnet comes to rest showing
north and south directions in all the cases.
Conclusion: A freely suspended magnet always comes to rest
pointing at north and south directions.

3. Like poles of magnets repel and unlike poles attract

The north pole of a magnet pushes away the north pole of the another
magnet. Similarly, the south pole of a magnet pushes away the south
pole of another magnet. But, when the north pole of a magnet is
brought near the south pole of another magnet, they attract each
other.

Activity 7.4
To show that like poles of magnets repel and unlike poles attract.

Materials required: Two bar magnets, a piece of thread, stand, etc.

Procedure
1. Tie a bar magnet at its middle with a thread and suspend it in
a stand. Maintain the bar magnet in a horizontal position.
2. Take the north pole of an another magnet near the north pole
of the suspended magnet. What happens? Observe.
3. Now, take the north pole of the another magnet near the south
pole of the suspended magnet. What happens? Observe.

Observation: The north pole of a magnet pushes away the north
pole of another magnet. The north pole of a magnet attracts the south
pole of the another magnet.

Conclusion: Like poles of magnets repel and unlike poles attract.

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4. The magnetic force is strong at the poles and weak at the middle

A magnet has a magnetic force. This force is strong at the poles and
weak at the middle.

Activity 7.5

To show that a magnet has more magnetic force at its poles.

Materials required: A bar magnet, iron llings or iron nails, etc.

Procedure
1. Take some iron llings in a
plate.
2. Roll a bar magnet over the
iron llings and observe.

Observation: You will see that
the iron llings will be stuck to
the two ends of the bar magnet
making a large group. No iron
llings will be stuck in the middle
of the magnet.

Conclusion: The magnetic force is strong at the poles and weak in
the middle.

5. Magnetic poles always exist in pair

A magnet with a single pole is
impossible. It always contains two,
i.e. north and south poles. If a bar
magnet is broken into two pieces,
each piece forms its own north and
south poles and becomes a complete
magnet. If the pieces are further
broken, each new piece will have two
poles again. It means that the poles
of a magnet can never be separated
because they always exist in a pair.

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Test for magnetism

A magnet attracts magnetic substances. It also attracts another
magnet. We can distinguish a magnet from a magnetic substance
with the help of following tests:

1. Testing the repulsion between the two poles

Perform the following experiment to test whether the given substance
is a magnet or a magnetic substance.

a. Suspend the given substance
in a stand with the help of a
thread.

b. Bring N pole of a bar magnet
near one of the poles of the
suspended substance. Then
observe whether there is
attraction or repulsion.

c. Again bring S pole of the bar magnet near the same pole of the
suspended substance. Observe whether there is attraction or
repulsion.

If there is attraction with both the ends of the magnet, the suspended
substance must not be a magnet. It must be a magnetic substance.
But, if there is repulsion with one pole of the magnet and attraction
with the other, the suspended substance must be a magnet. It is
because there is repulsion only when the suspended substance has
north and south poles, i.e. it is a magnet. Hence, repulsion is the sure
test for magnetism.

2. Testing the directional property of the given substance
A freely suspended magnet always comes to rest pointing north
and south directions. But a magnetic substance may point at any
directions while coming to rest. To test whether the given substance
is magnet or not, suspend the given substance in a stand and allow
it to move freely. It will come to rest after some time. Observe the
directions to which it is pointing and make it move. If the substance
points the same directions (i.e. north and south) in all cases, then
the given substance must be a magnet. Otherwise, it is a magnetic
substance.

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Uses of magnets

Ancient people used natural magnet, i.e. loadstone to nd the
direction. But at present, magnets have got a variety of uses. Some
of the uses of magnets are given below:

1. Magnets are used in many devices such as radio, television,
computer, speaker, telephone, etc.

2. They are used to make magnetic compass, magnetic toys,
magnetic tapes, etc.

3. They are used in iron industries to lift heavy loads.
4. They are also used to separate magnetic substances from

non-magnetic substances in the industries.
5. They are used in hospitals to remove iron or steel particles from

the eyes or wounds of patients.
6. They are used in generators to produce electricity by a

phenomenon called electromagnetic induction.
7. A magnet is also used in bicycle dynamo.

Main Points to Remember

1. A magnet is a substance which attracts magnetic substances
and always comes to rest showing north-south directions
when suspended freely.

2. The substances which are attracted by a magnet are called
magnetic substances.

3. The substances which are not attracted by a magnet are
called non-magnetic substances.

4. The end of a freely suspended magnet which points towards
the north is called north pole.

5. The end of a freely suspended magnet which points towards
the south is called south pole.

6. A magnet has the following properties:
a. A freely suspended magnet always comes to rest showing
the north-south directions.
b. A magnet attracts magnetic substances.

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c. Like poles of magnets repel each other but the unlike
poles attract.

d. The magnetic force is strong at the poles and weak in
the middle.

e. The magnetic poles always exist in pair.
7. Repulsion is the sure test for magnetism.

Exercise

1. Choose the best alternative in each case:

a. Natural magnet

i. Bar magnet ii. Lodestone

iii. Magnetite iv. Both ii and iii

b. Which of the following is not a magnetic substance?

i. Iron ii. Copper

iii. Nickel iv. Cobalt

c. Which of the following sentences is incorrect?
i. A magnet attracts magnetic substances.
ii. A freely suspended magnet comes to rest showing north
and south directions.
iii. A magnet produces current in a conducting wire.
iv. Like poles of magnet repel and unlike poles attract.

d. Which is the sure test for magnetism?

i. Attraction ii. Strength

iii. Repulsion iv. Induction

e. Where is a magnet used?

i. Computer ii. Radio

iii. Television iv. All of these

2. Answer these questions in very short:

a. What is a magnet?
b. What is a loadstone?

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c. Who found loadstone for the rst time?
d. Which directions does a freely suspended magnet show while

coming to rest?
e. Name some devices in which a magnet is used.

3. Give reasons:

a. A magnet attracts iron but not copper.
b. Repulsion is the sure test for magnetism.
c. A freely suspended iron rod may not come to rest showing

N-S directions.
d. Articial magnets are more useful than the natural magnets.

4. Differentiate between:

a. A magnet and a magnetic substance
b. Natural and articial magnet
c. North and south poles of a magnet

5. Answer these questions in detail:

a. Explain the terms magnet and magnetic substances with
examples.

b. What are articial magnets? Draw the diagrams of different
kinds of articial magnets.

c. Make a list of properties of a magnet.
d. How do you nd the poles of a magnet?
e. How do you test whether the given substance is a magnet or

not?
f. Write down the uses of magnets.
g. How can you show that a magnet is strong at poles and weak

in the middle?

Project Work

Take two bar magnets and use them in different ways to demonstrate
all the properties of a magnet. Write your experiment, observation
and conclusion separately in each case and show your teacher.

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Chapter

8 ELECTRICITY
Estimated periods:4

OBJECTIVES
At the end of the lesson, the students will be able to :
Ü dene electricity;
Ü mention sources of electricity;
Ü demonstrate simple electric circuit;
Ü dene and demonstrate conductors and insulators.

MIND OPENERS
Ü Which energy is used for running fridge, micro oven,

computers, television and washing machine?
Ü Can you tell some devices which produce electricity?
Ü Can electric current pass through metal and plastics? Discuss.

Introduction

We run various devices such as radio, television, computer, fridge,
fan, heater, etc by using electricity. Electricity is our good friend.
Nowadays, it is an essential part of our life. We can convert electricity
into heat energy, light energy, chemical energy and mechanical
energy.

Thus, electricity is a kind of energy which can be converted into heat,
light, mechanical, sound, etc by using suitable devices.

Sources of electricity

The devices that produce electricity are called sources of electricity.
Cell, dynamo, and generator are the sources of electricity.

Cell

A cell is a device that changes chemical energy into electrical energy.
A group of cells is called battery. Cells are of various types. Here, we
discuss only three types of cells.

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a. Simple cell

A simple cell consists of a container
of glass or plastic. It contains water
with few drops of sulphuric acid. Two wire

plates: one copper plate and another
zinc plate are dipped into the water.
Copper plate works as positive (+ve)
electrode and zinc plate works as
negative (-ve) electrode. Current
is produced inside this cell due to
chemical reaction. When positive terminal and negative terminal are
connected with a wire to a bulb, the bulb glows.

b. Dry cell

Dry cell is a commonly used
cell. It does not contain any
liquid. It contains a container
of zinc. Paste of ammonium
chloride surrounds the
inner wall of the container.
Mixture of carbon powder
and manganese dioxide is
kept inside the container. In
the middle, there is a carbon
rod with metal cap.
Inside the cell, chemical
reaction occurs. As a
result, electrical energy
is produced. Zinc acts as
negative terminal and carbon rod acts as positive terminal.
When positive terminal and negative terminal of the cell are
connected, current ows.
A dry cell is advantageous over simple cell. It is because it uses a
paste instead of liquid as an electrolyte. It has a small size and is
easy to handle. It is stronger and more durable than a simple cell.

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c. Photo-cell

A photo-cell converts light energy into
electrical energy. It is used in solar
calculator, solar car, solar trafc light
and other solar devices. When sun light
falls on the photo-cells, electricity is
produced. A large number of photo-cells
are used in solar panel.

d. Generator and dynamo

Generator and dynamo also
produce electricity. They convert
mechanical energy into electrical
energy. Generally, dynamo is
used in bicycle to produce small
amount of current. But generators
are used in factories to produce
large amount of current. Dynamo
and generator both contain a coil
and a magnet kept nearer to each
other. When magnet or coil comes
in motion, current is produced in
the coil. In hydroelectric power station, owing water rotates the
turbine connected to the generator. The generator in return converts
the kinetic energy into electrical energy.

Electric circuit
Activity 8.1

Take a dry cell, 2 pieces of wire and a bulb. Connect one end of one
wire to positive terminal of the cell and one end of the another wire
to negative terminal of the cell. Connect other ends of both wires to
the bulb. What do you observe?
You will observe the glowing of the bulb. Here the bulb glows due to
the ow of current from the cell to the bulb. Thus, electric circuit is
formed.

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The path through which electric current ows is called electric circuit.

Source, load and conducting wires are required to make an electric
circuit.

Cell, generator, dynamo, etc are sources, wire is a conducting wire
and the devices which use electricity are loads. Here, bulb is the load.
Switch is also kept in the electric circuit to break the circuit when the
device is not in use.

Open circuit and closed circuit

Open circuit

The circuit through which current
is not owing is called open circuit.
In open circuit, the switch is off
between the load and the source.

Closed circuit

The circuit through which current
is owing is called closed circuit. In
closed circuit, the switch is on.

Conductors and insulators

There are various types of substances around us. Some of them allow
current to pass through them whereas others do not.

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The substances which allow current to pass through them are called
conductors. Copper, aluminium, silver, graphite, wet wood, etc are
example of good conductors.
The substances which do not allow current to pass through them are
called insulators. Glass, dry wood, plastic, paper, etc are insulators.

Semi-conductors

The substances which allow only less amount of current to pass through
them are called semi-conductors. For example, silicon, arsenic,
germanium, etc. They behave as conductors at high temperature.

Activity 8.2

Take a dry cell, one torch, bulb and
three pieces of wire. Connect the dry
cell to the bulb as shown in the gure.
There must be a gap between A and B
as shown in the gure.

Collect a piece of wire, pencil, cork,
plastic, wood, a piece of stone, etc. Place them in the gap between A
and B turn by turn. What ndings do you get? Record the result in
the following table.

Sn. Materials Bulb glows or not Conductor/Insulator
1. Copper wire
2. Plastic Glows Conductor
3.
4. Does not glow Insulator
5.
6.

Main Points to Remember

1. Electricity is a form of energy which is required to run devices
like computer, refrigerator, television, fan, heater, etc.

2. Cell, dynamo and generator are various sources of electricity.
3. Simple cell consists of zinc plate as negative electrode and

copper plate as positive electrode.

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4. Dry cell consists of zinc vessel with carbon powder and
manganese dioxide tightly packed inside it.

5. Dynamo is used to produce small amount of current.
6. Generator is used to produce huge amount of current in

industries or factories.
7. The path through which electric current ows is called

electric circuit.
8. No current ows through open circuit whereas current ows

through closed circuit.
9. The substances which allow current to pass through them

are called good conductors.
10. The substances which do not allow current to pass through

them are called insulators.

Exercise

1. Choose the best alternative in each case:

a. A device that changes chemical energy into electrical energy is
called

i. Battery ii. Load

iii. Cell iv. Dynamo

b. The chemical used in a simple cell is

i. Carbon ii. MnO2

iii. CuSO4 iv. H2SO4

c. The chemical that is used in a dry cell

i. NH4Cl ii. MnO2
iii. Carbon dust iv. All of these

d. The circuit through which current is not owing is called

i. Open circuit ii. Closed circuit

iii. Mixed circuit iv. All of these

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e. Which of the following is a semi-conductor?

i. Silicon ii. Graphite

iii. Diamond iv. Silver

2. Copy the correct statement and correct the wrong statement:

a. Computer, electric heater, rice cooker and micro oven run
with electricity.

b. Cell, dynamo, and generator are loads of electricity.
c. Dry cell contains sulphuric acid.
d. Generator contains magnet and coil.
e. Open circuit is formed when switch is on.
f. Load, conducting wire and source are required to make

electric circuit.
g. Metals, plastic, green wood, etc are good conductors of

electricity.

3. Answer these questions in very short:

a. What is electricity? Give some examples of source of electricity.
b. What are the two electrodes of a simple cell?
c. How does a dry cell produce electricity?
d. What is a dynamo?
e. What is electric circuit?
f. What is open circuit?
g. What is good conductor? Give some examples of good

conductors.
h. What is insulator? Give any four examples of insulators.

4. Answer these questions:

a. Explain the structure of a dry cell with diagram.
b. Draw an electric circuit and label important parts.
c. How can you test whether a given substance is an insulator

or a good conductor?

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d. Differentiate between open circuit and closed circuit.
e. Differentiate between conductor and insulator.
5. Study the given gure and label important parts:

Project Work

a. Take a dry cell, and take out its cover one by one. Observe the
materials contained inside it.

b. Take a dry cell, connecting wire and a torch bulb. Connect the
bulb to the cell with the help of connecting wire to make an
electric circuit.

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Chapter

9 MATTER
Estimated periods: 8

OBJECTIVES
At the end of the lesson, the students will be able to:
Ü dene matter;
Ü tell the physical properties of matter;
Ü tell different states of matter;
Ü tell the conditions for the change in state of matter;
Ü dene element, compound and mixture and classify matter

as element, compound and mixture.

MIND OPENERS
Ü Can you say what matter is?
Ü What are different states of matter? Can matter be changed from

one state to another state? How?
Ü Can you say the differences between pure water and tea? Discuss.

Introduction

There are various things around us. We nd trees, stones, soil,
buildings, chair, tables, water, air, etc around us. All of them are
matters.

Most of the matters can be seen with naked eyes but some of them
cannot be seen. We can see milk, water, book, table, bus, building, etc
but cannot see gas, air, etc. Matter remains in different forms with
different properties. But, all of them have two common properties.
They are: they have mass and they occupy space.

Matter is anything that occupies space and has mass.

Mass of an object is total quantity of matter contained in it. Due to
mass, an object is heavy and has weight. In general, bigger object has

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more mass and smaller object has less mass.

An object occupies space. It means an object needs space to exist. The
total space occupied by an object is called its volume. Bigger objects
have more volume and smaller objects have less volume.

Activity 9.1

To show that air occupies space

Materials required: An empty bottle, a bucket of water

Procedure
1. Take an empty bottle and a bucket of water.
2. Invert the bottle and dip the mouth of the
bottle inside water. What do you nd?

Observation: You can see air bubbles coming
from the bottle. Here, inside the bottle, there was
air that could not be seen. The air comes out when
the water goes inside the bottle. The water takes the space of air.

Conclusion: Air also occupies space, i.e. air also has volume.

Activity 9.2

To show that air has mass

Materials required: Two balloons of equal size, a rod, a thread, etc.

Procedure
1. Take two balloons of equal size.
2. Inate both of them to equal size.
3. Take a rod and suspend the rod with a thread.
4. Fix the thread to a nail.
5. Suspend balloons one to each end of the rod so that the rod
remains horizontal as shown in the gure.

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6. Make holes in one of the balloons with a
hot needle. What happens?

Observation: The air comes out from the holes
of the balloon and its mass decreases whereas
mass of the another balloon remains constant.
So, the bar inclines towards that balloon which
is not broken.

Conclusion: The balloon having more mass is
heavier and it makes the rod incline downwards.

Atoms and molecules

All matters are composed of small particles. These small particles
are called molecules. The molecules are so small that they cannot
be seen with naked eyes. Thus, molecules are the smallest particles
of a substance which can exist freely and contain all properties of the
substances.

Molecules are attracted with each other by a force called intermolecular
force. There is a space between molecules called intermolecular space.

Inter-molecular Gas
space

Solid

Liquid molecules

Solid molecules Liquid molecules Gas molecules

The molecules of solids are tightly packed. The molecules of liquids

are loosely packed while the molecules of gas are apart from each

other.

Molecules can also be further sub-divided into atoms. But, atoms
cannot be further divided. Atoms combine together to form molecules.
Atoms take part in chemical reactions.

Thus, an atom is the smallest particle of a matter which can take part
in a chemical reaction.

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Differences between atoms and molecules

Atoms Molecules

1. An atom is the smallest 1. Molecules are the smallest
particle of an element which particles of a substance
can take part in chemical which can exit freely and
reaction. contain all properties of the
substance.

2. Atoms cannot be further 2. Molecules may be further
divided. divided into atoms.

States of matter

Matter exists in three states. They are solid, liquid and gas.

Solid

Solid substances have their xed shape and volume.
Generally, they are hard and rigid. Intermolecular
space is less but intermolecular force of attraction is
high. Due to this, molecules in solid are tightly packed.
Because of tightly packed molecules, solid cannot be
compressed.

Liquid Solid molecules
Liquid molecules
Liquid substances have xed volume but not xed
shape. Liquid gains the shape of the container
in which it is kept. In liquid, molecules are loosely
packed. Intermolecular force is less than that in solid
but more than that in gas. Similarly, intermolecular
space in the liquid is more than that in solid but less
than that in the gas.

Therefore, liquid molecules can ow easily keeping
the distance between them constant. Thus, the liquid
has xed volume but not xed shape.

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Gas

Gases have neither xed shape not xed volume.
Molecules in gases are loosely arranged. Intermolecular
force is the least but the intermolecular space is the
highest. Due to this, molecules in gases can spread
freely. Gases can be compressed in a tyre, football,
balloon, etc.

Gas molecules

Activity 9.3

To show that a liquid has xed volume but a gas does not have

Materials required: Syringe, water, etc.

Procedure

1. Take a syringe without needle.

2. Pull the piston to the maximum level.

3. Block the hole of the syringe with a thumb, then push the
piston. What happens?

Syringe tube

Water Piston

Again ll the syringe with water and repeat the above activity. What
happens?

Observation: You can compress the air but you cannot compress the
water.

Conclusion: A gas has no xed volume but a liquid has xed volume.

Change in state of matter

Matters can be changed from one state to another by heating or
cooling. This process is called change in state of matter.

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Melting

When solid substances are heated, molecules absorb heat. Due to
this, intermolecular force decreases but the intermolecular space
increases. Thus, solid changes into liquid. This process is called
melting.

Activity 9.4

To show melting process
Materials required: A beaker, ice cubes, etc.

Procedure

1. Take some ice cubes in a
beaker.

2. Heat the beaker by using gas
burner or spirit lamp. What
happens?

Observation: The ice melts into liquid water.

Freezing

When a liquid substance is cooled, intermolecular space decreases
but the intermolecular force increases. Due to this, liquid substance
changes into solid state. This process is called freezing. This process
is also called solidication.

Activity 9.5

Take a candle and burn it. What do you nd after some time?

The candle melts. Most of the melted wax is used for burning.
A small part of wax ows down. When the wax owing
downward cools, it freezes to solid. Here, freezing into solid
is due to cooling.

Evaporation

When liquid substance is heated, intermolecular space increases but
the intermolecular force decreases. Due to this, molecules are free to
move and liquid converts into gas. This process is called evaporation.

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Condensation

When a gas is cooled, intermolecular space decreases but
intermolecular force increases. Due to this, a gas converts into liquid.
This process is called condensation.

Activity 9.6

To show evaporation and condensation

Materials required: Kettle, burner, a plate, ice cubes, etc.

Procedure

1. Take a kettle and put little water
inside it.

2. Heat the kettle with gas burner
or spirit lamp. The water boils
and water vapour comes out from
the spout.

3. Put a plate containing ice just
above the vapour. What happens?

Observation

You will see small droplets of water being formed from water vapour.

Conclusion

Here, at rst, evaporation occurs due to heat then condensation
occurs due to cooling.

Sublimation

Some substances like camphor, ammonium chloride, etc directly
change into vapour when heated. They convert directly, into solid
from the vapour when cooled. This process is called sublimation.

The process of changing of a solid into vapour on heating and vapour
back into solid on cooling is called sublimation.

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Activity 9.7

To show the process of sublimation

Materials required: An evaporating basin, camphor, funnel, a test
tube, cotton, etc.

Procedure

1. Take some pieces of camphor in an evaporating basin.
2. Cover it with an inverted funnel.
3. Put a test tube over the stem of funnel.
4. Put wet cotton around the test tube.
5. Heat the basin with gas burner or spirit lamp.

Camphor Cotton
Evaporating basin Test tube

Funnel

Tripod Stand Burner

The process of sublimation
Observation: You can see the changing of solid camphor into vapour.
The vapour camphor converts into solid due to cooling by wet cotton.
The solid camphor gets deposited in the inner walls of test tube.

Conclusion: The camphor shows the process of sublimation.

Uses of change in state of matter

Change in the state of matter due to heating and cooling has many
uses in practical life. Some of the uses are as follows:

1. Rain occurs due to change in state of matter. Water of ocean or
river vapourizes due to the heat of the sun. The water vapour
mixes with other gases and cloud is formed. When cloud reaches
the cold place, the water vapour condenses to the water. Thus,
rainfall occurs.

2. The clothes after washing are kept in the sun for making it dry.

Times' Crucial Science and Environment 96 Book 6