Oasis Science and Technology 4

Summary

1. The mixture of gases present on the earth is called air.
2. Air is odourless, colourless and tasteless matter.
3. Air exerts pressure.
4. Air flows from colder places to hotter places.
5. Monsoon brings rain from the ocean upon land.
6. Air is filled in bicycle tubes and football.
7. The mixing of harmful gases, dust and germs in the air is called

air pollution.
8. Industries should be very far away from cities and villages.

Model Questions with Their Answer

1. What percentage of air is occupied by nitrogen gas?
78% of air is occupied by nitrogen gas.
2. Which wind brings rain in Nepal?
The monsoon wind brings rain to Nepal.
3. Why is air pumped into the football?
Air is filled in football because air will occupy volume inside

football. It makes the ball light and bouncy.
4. Why should we reduce the use of petroleum?
We should reduce the use of petroleum because it produces

smoke. Smoke pollutes the air.

5. Observe the diagram and answer the following questions.
i. What is shown in the diagram?
Forest is shown in the diagram.

ii. What kind of air is found in it?
Fresh and healthy air is found in it. It has a lot of oxygen in

it.

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iii. Why is it cool around the forest?

It is cool around the forest because there is less carbon
dioxide around the forest.

Exercise

1. Fill in the blanks with an appropriate word. air
shape molecules colder places pressure

a. A mixture of various gases is called …………
b. Air exerts ………..
c. Air …………. are very loose.
d. Air flows from ………. to hotter places.
e. Air cannot maintain its …………. and volume.

2. Write true for the correct and false for the incorrect statement.

a. When air is filled in a bicycle tube, it pushes the wall of the
tube.

b. Air doesn’t have mass and weight.

c. If we put a little amount of air in a large container, air will
expand and cover the entire container.

d. Air flows from hot places to cold places.
e. Air helps plants in the pollination and dispersal of seeds.

3. Choose the best answer from the given alternatives.
a. What is the mixture of gases called?

Air Wind Atmosphere Gas
b. What is the colour of air?

Red Light yellow Brown Colourless
c. What is the taste of air?

Salty Sweet Sour Tasteless

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d. Which one of the following pollutes air?

Smoke Dust Industrial gases All of them

e. What is the best way to keep the air fresh?

Afforestation Deforestation Industrialization Urbanization

4. Match the following.

Nitrogen 21%

Oxygen 78%

Burning windmill

Air pollution oxygen gas

Wind decreases the quality of air

5. Answer the following questions in a word each.
a. What is the layer of air around the earth called?
b. What device changes the energy of the wind into electricity?

c. What is the property of air called that pushes the wall of the
container?

d. In which state of matter does air exist?
e. Where does the wind start from?

6. Give reason.
a. We can’t see air.

b. People in the city suffer more from lung diseases than the
people in the village.

c. Bubbles are seen when we blow air inside water with a straw.

7. How is air in the village different from the city? List any two
points.

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8. Compare the condition of air between these two places that are
shown in the diagrams.

(a) (b)

9. Answer the following questions.
a. What is air?
b. Write any three properties of air.
c. List any three natural uses of air.
d. How do humans use air?
e. What is air pollution?

f. Air in the city is harmful to our health. What are the reasons
for the poor quality of air in the city?

g. What should people in the city do to improve the quality of
air?

h. What are the harmful effects of air pollution?

10. Project work.

Talk to your parents, guardians and other family members. Do
they have any diseases caused by pollution? How often do people
get sick because of an unhealthy environment? Discuss in a group.

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Unit Rock
6.3

Key terms and terminologies

1. Rock: Rock is a solid hard substance found on the surface of the earth.
2. Soft rocks: The rocks that break easily are called soft rocks.
3. Hard rocks: The rocks that do not break easily are called hard rocks.
4. Soil: Soil is a weathered rock.
5. Weathering: The process in which a rock breaks into powder naturally is

called weathering.
6. Boulder: A boulder is a very large rock.
7. Soapstone: Soapstone is a soft rock made of talc and other minerals.

Introduction

Earth has a solid landmass. This solid landmass is made of rock and
soil. Rock is a solid hard substance found on the surface of the earth.
It is made up of minerals. Minerals are useful substances found on
the earth. Rock is a matter. It is in solid form. Some rocks contain lots
of minerals but some contain fewer.

diamond sandstone emeralds
fig: some rocks around us

Physical properties of the rock are listed below
i. Rock is a solid substance.
ii. Some rocks are hard and some are soft.
iii. Some rocks are shiny and some are not.
iv. Some rocks have metal in them and some do not.

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v. Different rocks have different colours.
vi. Rocks are found in different shapes and sizes.

Activity
Find a pebble. Observe and list out its characteristics.

Fact file
Molten rock is called magma.

Resonable facts
Why do different rocks have different colours?
Different rocks have different colours because they are
made up of different minerals.

Types of rocks

There are various forms of rock. Broadly rock is divided into two
groups. They are soft rock and hard rock. Soft rock breaks easily.
Plants can grow easily on the hills made of soft rock. Soapstone and
chalk are some soft rocks. Diamond and granite are hard rocks. We
cannot break them easily. Hammer and crusher machines can break
them. Plants cannot grow easily on the hard rock hills.

soft rock: mudstone soft rock: chalk

hard rocks: granite hard rock: sandstone
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Importance of rock

Rock is a very important part of the environment.
Natural importance of rock are:
i. It makes land.
ii. It changes into the soil.
iii. Bedrock stores water.
iv. Rock makes hills and mountains.

weathered rocks form soil bedrocks store water

Uses of rocks

Human beings use rocks in many ways.
i. We use rocks to pave the path.
ii. Rocks are used to make houses and bridges.
iii. Shiny and colourful rocks are used for decoration.
iv. Diamond is used for making ornaments.
v. Gold and silver can be produced from rock.
vi. Rock can be used to make statues.

stone paved path diamond necklace house made of stone making idols from rocks

fig: uses of rocks

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Fact file
The layers of soil are called a soil profile. The top one
is topsoil and the bottom one is bedrock.

Resonable facts
Why do plants grow in the soil?
The plants grow in the soil because the soil has
minerals. Soil is softer than rock.

Soil

Soil is the weathered rock. Rainfall, sunshine, day and night, change
in season and wind are common activities. When these activities affect
rock for thousands of years, the rock will crumble away. Continuous
heating and cooling for many years will crack the rock. Friction from
wind and water erodes the rock. After thousands of years, it will
change into fine powder. The process in which a rock breaks into
powder naturally is called weathering. Decaying plant and animal
parts will mix in powdered rock over time. Thus the soil is formed.

water erodes rock tree roots break rock humus mixes in the soil

Activity

Collect 10 gram of soil and put in a cup of water. Observe
very carefully. Do you see any plant materials? Does it
contain humus?

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Summary

1. The landmass is made of rock and soil.
2. Rock is a solid hard substance found on the surface of the earth.
3. Minerals are useful substances found on the earth.
4. Some rocks are very small and some of them are very big.
5. Plants can grow easily on the hills made of soft rock.
6. Plants cannot grow easily on the hills made of hard rock.
7. Shiny and colourful rocks are used for decoration.
8. Soil is the weathered rock.
9. The process in which a rock breaks into powder naturally is called

weathering.
10. Decaying plants and animal parts will mix in the soil.

Model Questions with Their Answer

1. What is a mineral?
Useful substances found in the land are called minerals.

2. What makes the soil fertile?

Humus makes the soil fertile. Humus is a black decaying organic
matter.

3. Why does rock have different colours?
Rock has different colours because it contains different minerals.

4. Write any three characteristics of rock.
The characteristics of the rock are listed below:

i. It is solid.
ii. Different rocks have different colours.
iii. Rocks are found in different shapes.

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5. List any three points to show the importance of rock.
The importance of the rock is noted below:

i. We use rocks to pave the path.
ii. Shiny and colourful rocks are used for decoration.
iii. Rock can be used to make statues.

Exercise

1. Fill in the blanks with an appropriate word. plants
hard rocks soft rocks rock minerals

a. A solid hard object found on the surface of earth is called
……………

b. Useful substances found on the earth is …………..

c. Hills made of soft rocks are good for ………… to grow.

d. Soapstone and chalk are …………

e. Crusher machine can even break ……….

2. Write true for the correct and false for the incorrect statement.
a. Plants can grow easily on the hills made of hard rock.
b. Rock is a very important part of the environment.
c. We use a rock to pave the path.

d. Continuous heating and cooling for many years will make
rock strong.

e. Friction from wind and water erodes rock.

3. Choose the best answer from the given alternatives.
a. Which one is a hard rock?

Chalk Diamond Mudstone All of them

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b. What is a rock made from?

Water Minerals Vitamins None

c. Which one is a soft rock?

Sandstone Granite Diamond Soapstone

d. What type of rock can be broken very easily?

Soft rock Hard rock Both of them None of them

e. What is soil?

Weathered Igneous Sedimentary Metamorphic

rock rock rock rock

4. Match the following. soft rock
Rock mixture of minerals
Sandstone hard rock
Diamond ornament
Weathered rock soil
Mudstone

5. Answer the following questions in a word each.
a. What is a solid hard natural object found on land called?
b. In which type of rock plants grow easily?
c. Which rock holds underground water?
d. What is the process in which the rock changes into powder?
e. What is the weathered rock called?

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6. Write any two differences between:
a. Hard rock and soft rock
b. Rock and soil

7. Give reason.
a. Diamond is used to make ornaments.
b. A plant can grow easily on hills with soft rock.

8. Study the given diagram and answer the following questions.
i. Why does rock erode?
ii. What happens when rock is eroded?

9. Answer the following questions.
a. What is rock?
b. Write any three uses of rock.
c. Write any three properties of rock.
d. What are the natural uses of rock?
e. What is soil? How is it formed?

10. Project work.

Visit your nearby places and observe rocks. Do you find any soft
rock? Discuss with your friend.

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7UNIT Energy

Introduction

The bus gets the energy to move from petroleum. The computer gets
the energy to run from electricity. The watermill runs from the energy
present in the flowing water. The energy of the wind rotates the
windmill. Energy is necessary to do any work. Energy is the capacity
of doing work. Energy present in one substance may be different from
the energy present in another substance.

Bus is powered by diesel electric bus is powered by battery

computer runs on electricity water mill runs on hydropower

fig: energy is necessary to do work

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Unit Introduction to energy
7.1

Key terms and terminologies

1. Energy: The capacity of doing work is called energy.
2. Heat energy: The form of energy that gives the sensation of warmth is called

heat energy.
3. Sound energy: The form of energy that gives the sensation of hearing is

called sound energy.
4. Electrical energy: The energy produced by flowing electrons is called

electrical energy.
5. Magnetic energy: The energy present in a magnet is called magnetic energy.
6. Light energy: The form of energy that gives the sensation of vision is called

light energy.
7. Chemical energy: The energy stored in a chemical substance is called

chemical energy.
8. Sources of energy: The substances that can produce energy are called the

sources of energy.

Introduction

We need energy to do work. We get energy from food. Walking,
running, cooking food, gardening and studying are daily activities.
These activities use energy. When energy is finished in our bodies,
we feel tired. We need to eat again and sleep to regain our energy.

food provides us energy energy is necessary to play
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Light energy helps us to see. Sound energy helps in talking. We use
machines every day. Fans, TVs, radios, blenders, remotes etc. run on
electricity. We need more energy to do heavy work. We need less
energy to do light work. An adult can carry a desk because he or she
has the necessary energy. A child, with less energy, cannot carry the
same desk.

kids carrying school bag a peron carrying a rice sack

fig: more energy is needed to do heavy work

Fact file
A single wind turbine can produce electricity for upto
1400 homes.

Resonable facts
Why do we need energy in our body?
We need energy in our body because it helps us to walk,
speak and study.

Types of energy

The energy present in the food is different from the energy present in
the ringing bell. Energy from the sun is different from the energy
present in flowing water. Energy is found in different forms. Heat
energy, light energy, sound energy, electrical energy, magnetic energy
and chemical energy are a few different forms of energy.

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Heat energy

Our body is warm because it contains heat. We feel warm near the
fire in winter. The form of energy that gives us the sensation of warmth
is called heat energy.

The sources of heat energy are sun, burning firewood, burning
petroleum and electrical devices such as a heater.

burning firewood electric heater sun coal powers the steam
engine of train
fig: sources of heat energy

Uses of heat energy:
i. Heat energy from the sun runs water cycle.
ii. It helps us to cook food.
iii. It helps us to iron clothes.
iv. It helps us to run steam engine.

Activity

Make a list of sources of heat energy that your family
uses in the winter season.

Fact file
Heat energy moves from hotter objects to colder objects.

Resonable facts
Why is heat called an energy?
The heat is called energy because it can do work. For
example, heat from the sun powers the water cycle.

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Sound energy

We listen to the song. We can hear the ringing of the school bell. The
form of energy that gives us the sensation of hearing is called sound
energy.

The sources of sound energy are clapping, speaking, horns, speakers
etc.

loudspeaker tuning fork pressure horn
fig: sources of energy

Uses of sound energy
i. It helps us to speak and sing.
ii. It helps us to study.

Electrical energy

The energy produced by flowing electrons is called electrical energy.

Electric cells and generators are the sources of electricity.

generator bicycle dynamo solar plant

fig: sources of electricity

Uses of electricity

i. To operate mobiles and computers.

ii. To run electrical devices such as irons, fans, etc.

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Fact file
The storm is one of the main cause of load shedding.

Magnetic energy
A magnet can pull magnetic substances. The energy present in a
magnet is called magnetic energy.
Loadstone, bar magnet and earth are the sources of magnetic energy.

loadstone U-shaped magnet bar magnet
fig: source of magnetic energy

Uses of magnetic energy

i. It is used to make a speaker.

ii. It is used to make an electric bell.

iii. It is used to make a generator.

Light energy

Eyes can see. Can we see in the dark? No, we cannot. Light is necessary
for our eyes to see. The form of energy that gives us the sensation of
vision is called light energy.

Sunlight, bulb and fire are the sources of light energy.

sun bulb fire

fig: sources of light energy

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Uses of light energy
i. The plants use it for making food.
ii. It helps animals to see.
iii. It is used to take photographs.

Fact file
Light travels 3000 km per second.

Resonable facts
Why is sunlight necessary during photosynthesis?
Sunlight is necessary during photosynthesis because the
light is the source of energy for photosynthesis.

Chemical energy

Firewood, food and coal are chemical substances. They contain energy
in them. The energy stored in a chemical substance is called chemical
energy.

fruits contain chemical energy medicine contains coal contains chemical
chemical energy energy

fig: source of chemical energy

Uses of chemical energy
i. Petroleum runs vehicles and machines.
ii. Food gives energy for living things.
iii. Medicines help in healing wounds.

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Activity
Even though we don't do physical activities, we get tired
and hungry after a few hours. What is the energy used
for?

Sources of energy

Wind and flowing water can produce electrical energy. Burning
firewood gives heat and light. The sun is the ultimate source of energy.
It gives us heat and light. The substances that can produce energy are
called sources of energy. Sun, wind, firewood, coal etc. are the natural
sources of energy.

sun wind firewood coal

fig: natural sources of energy

Battery, briquette, hydroelectricity are artificial sources of energy.

battery briquette hydroelectricity
fig: artificial sources of energy

Sources of energy such as petroleum are in limited amounts on the
earth. They will be finished in the near future. Sources of energy such
as the solar energy are in unlimited amounts. They will not be finished.

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Resonable facts

Why is hydroelectricity called an artificial source of
energy?

Hydroelectricity is called an artificial source of energy
because it is produced by human technology.

Summary

1. The capacity of doing work is called energy.

2. We need more energy to do heavy work.

3. Children cannot carry a desk because they have less energy.

4. The energy present in food is different from the energy present in
a ringing bell.

5. Heat energy, light energy, sound energy, electrical energy,
magnetic energy and chemical energy are a few forms of energy.

6. The form of energy that gives the sensation of warmth is called
heat energy.

7. The form of energy that gives the sensation of hearing is called
sound energy.

8. The energy produced by flowing electrons is called electrical
energy.

9. The energy present in a magnet is called magnetic energy.

10. The form of energy that gives the sensation of vision is called
light energy.

11. The energy stored in a chemical substance is called chemical
energy.

12. The substances that can produce energy are called the sources of
energy.

13. Some sources of energy such as solar energy are unlimited.

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Model Questions with Their Answer

1. Name any two devices that produce heat energy.
Two devices that produce heat energy are heaters and electric

irons.

2. Write the name of any two natural sources of light.
The two natural sources of light are the sun and firefly.

3. Why do we need to eat food?
We need to eat food because it gives us energy.

4. The sun is called a natural source of energy. Why?
The sun is called a natural source of energy because the sun is a

natural star that gives solar energy.

5. Which sources of energy are used in villages? What are they
used for?

The sources of energy used in village are firewood, cow dung
and twigs.

They are used to make fire, cook food and boil water.

Exercise

1. Fill in the blanks with an appropriate word.

chemical sound energy energy petroleum heavy

energy works

a. The bus gets the energy to move from …………..

b. The capacity of doing work is called ……….

c. We need more energy to do …………

d. Form of energy that gives the sensation of hearing is …………

e. The energy stored in a chemical substance is called …………

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2. Write true for the correct and false for the incorrect statement.
a. The energy of the wind rotates the windmill.
b. We get energy from food.
c. When energy is finished in our bodies, we feel tired.
d. An adult can carry a desk because he/she has less energy.
e. Form of energy that gives sensation of hearing is light.

3. Choose the best answer from the given alternatives.

a. What is the source of energy for our body?

Electricity Medicine Food Firewood

b. What form of energy gives the sensation of vision?

Sound energy Heat energy Light energy Chemical
energy

c. What is the source of energy for the fan?

Heat energy Sound Light energy Electrical
energy energy

d. What form of energy gives the sensation of hearing?

Light energy Heat Sound energy Electrical
energy energy

e. What type of energy is present in food?

Magnetic Heat Light energy Chemical
energy energy energy

4. Match the following.

Sense of vision vehicles

Sense of hearing electricity

Food sound energy

Flow of electrons chemical energy

Petroleum light energy

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5. Answer the following questions in a word each.
a. What type of energy is present in a battery?
b. What type of energy is produced by the sun?
c. Which form of energy gives the sensation of warmth?
d. What form of energy is present in medicines?
e. Which form of energy is produced by torchlight?
6. Write any two differences between:
a. Heat energy and sound energy
b. Light energy and chemical energy
7. Give reason.
a. We need to eat food.
b. An adult can do heavy work but a child cannot.
c. The sun is called the ultimate source of energy.
8. Study the given diagram and answer the following questions.
i. What type of source of energy is firewood?
ii. What is it used for?
9. Answer the following questions.

a. What is energy?
b. Write any three uses of heat energy.
c. Mention some uses of sound energy.

d. For what purpose light energy is used?

e. Food has chemical energy. What is chemical energy used
for?

f. What is the source of energy?

10. Project work.

Why do we need to eat lots of nutritious food? Why do grown-
ups need to eat more food than us? Why does a cow eat a lot of
grass than the calf? Think about it.

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Unit Use of Electricity
7.2

Key terms and terminologies

1. Electrical energy: The form of energy produced by the movement of the
electrons is called electrical energy.

2. Source of electricity: The devices that can produce electricity is called the
source of electricity.

3. Cell: The cell is a device that changes chemical energy into electricity.
4. Battery: The group of cells is called a battery.
5. Photocell: The device that changes sunlight into electricity is called a

photocell.

6. Solar panel: The group of photocells is called solar panels.
7. Dynamo: The device that produces electricity by the rotation of the magnet

is called a dynamo.

8. Generator: The device that produces electricity by the rotation of the turbine
is called a generator.

9. Hydroelectricity: The electricity produced when the turbine rotates due to

flowing water is called hydroelectricity.

Introduction

Electricity is a very important form of energy. Almost every modern
machine runs on electricity. The form of energy produced by the
movement of electrons is called electrical energy.

Uses of electricity

Electricity is a unique form of energy. It can be changed into any other
form of energy. An electric iron can change it into heat energy. A light
bulb can change it into light energy. A radio uses electricity to produce
sound energy. Since it can easily change into other forms of energy, it
is widely used in the modern society.

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light bulb radio iron

fig: uses of electricity

Some of the common uses of electricity are listed below:
i. It is the source of energy for phones, televisions, computers, etc.

ii. It is used by bulbs and CFLs to produce light energy.

iii. It is used by rice cookers, heaters and irons to produce heat.

iv. It runs fridges, fans and vacuum cleaners.

v. Electric cars, trains and trolleybuses are powered by electricity.

vi. Electric bells, clocks and doorbells run on electricity.

Fact file
An electric eel, a fish, can produce 500 volts of current.

Activity
Make a list of devices that use electricity in your school.

Resonable facts
Why should we not play with electric wires?

We should not play with electric wires because
electricity can kill us.

Sources of electricity

The clock is powered by a battery. The laptop has a rechargeable

battery. Hydroelectricity is produced with the help of a generator.

Photocell can power CFLs. The devices that can produce electricity

are called the sources of electricity.

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Cell

The cell is a device that changes chemical energy into electricity.
Primary cells cannot be recharged. Secondary cells can be recharged.
The rechargeable battery is used in smartphones, electric cars and
laptops. The dry cell is used in torchlights and radios. It cannot be
recharged. A group of cells is called a battery.

Activity
Observe the simple cell in your science laboratory.
Draw a schematic diagram of this device.

simple cell dry cell rechagreable cell

fig: types of electric cells

Photocell solar panel

The device that changes sunlight into electricity is
called a photocell. It is kept on the sunny side of
the roof. It produces electricity and stores it in the
battery. A group of photocells is called solar
panels.

Fact file
China has the largest number of photocells.

Resonable facts
Why should we use solar panels on our houses?
We should use solar panels on our houses because they
are cheap and pollution-free.

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Dynamo

The device that produces electricity by the bicycle dynamo
rotation of the magnet is called a dynamo. It
contains a box with wires in it. There is a
magnet in the middle of the wires. The magnet
is connected to the turbine touching the tyre of
the bicycle. When the bicycle moves, the
turbine rotates the magnet. The rotating
magnet produces electricity.

Fact file
The first generator was made in 1660.

Generator

The device that produces electricity by the

rotation of the turbine is called a generator. It

contains a box with a powerful magnet in it.

There is a turbine in the middle of the magnet.

The turbine is placed in the path of flowing

water. Water is collected in a dam. This water generator
flows down the pipe into the turbine. When

the turbine rotates, electricity is produced. It is called hydroelectricity.

The turbine is sometimes rotated by wind.

Summary

1. The form of energy produced by the movement of the electron is
called electrical energy.

2. An electric iron can change electricity into heat energy.
3. A light bulb can change electricity into light energy.
4. A radio uses electricity to produce sound energy.

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5. The devices that can produce electricity are called sources of
electricity.

6. The cell is a device that changes chemical energy into electricity.
7. The device that changes sunlight into electricity is called a

photocell.
8. The device that produces electricity by the rotation of the magnet

is called a dynamo.
9. The device that produces electricity by the rotation of the turbine

is called a generator.

Model Questions with Their Answer

1. Define electrical energy.
The form of energy produced by the movement of electrons is

called electrical energy.
2. Why do people use a battery?
People use a battery because it is small and easy to use.
3. Dry cell is called source of electricity.
Dry cell is called source of electricity because it changes chemical

energy into electricity.
4. List the uses of electricity.
The uses of electricity are listed below:

i. It is the source of energy for phones, televisions and
computers.

ii. It is used by bulbs and CFLs to produce light energy.

iii. It is used by rice cookers, heaters and irons to produce heat.
5. We should increase the use of hydroelectricity in Nepal. Why?
We should increase the use of hydroelectricity in Nepal because

it is cheap and pollution-free. We have lots of fast flowing rivers
to harvest hydroelectricity in Nepal.

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Exercise

1. Fill in the blanks with an appropriate word.

sources photocells electricity sound battery

a. Almost every modern machine runs on ………

b. A radio uses electricity to produce ……… energy.

c. The clock is powered by …………

d. The devices that can produce electricity are called ………. of

electricity.

e. A group of ………… makes solar panels.

2. Write true for the correct and false for the incorrect statement.

a. The rotating magnet of the dynamo produces electricity.

b. The device that produces electricity by the rotation of the

turbine is called a photocell.

c. A light bulb can change current into light energy.

d. The laptop has a rechargeable battery.

e. The dry cell is used in computers.

3. Choose the best answer from the given alternatives.

a. What is used in a torchlight?

Dry cell Simple cell Dynamo Generator

b. Which energy runs the computer?

Light energy Sound Chemical Electricity
energy energy

c. What converts light into electricity?

Photocell Dynamo Generator Dry cell

d. Which of the given source produces hydroelectricity?

Dry cell Simple cell Dynamo Generator

e. What does an electric car need as the source of electricity?

Rechargeable battery Generator Dynamo Petroleum

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4. Match the following.
Fan light to electricity
Rice cooker electricity to sound
Light bulb electricity to heat
Radio electricity to light
Photocell electricity to motion
5. Answer the following questions in a word each.
a. What energy is produced by flowing electrons?
b. What is a group of photocells called?
c. What is the device that changes chemicals into electricity?

d. Which device contains a rotating magnet to produce
electricity?

e. What device contains a rotating turbine to produce electricity?
6. Write any two differences between:
a. Cell and photocell b. Dynamo and generator
7. Give reason.
a. A battery is called a source of electricity.
b. We should use electricity in cars instead of petroleum.
8. Study the given diagram and answer the following questions.

i. What form of energy is being produced in
the diagram?

ii. Which device is used to produce electricity?
9. Answer the following questions.
a. What is electricity?
b. List any three uses of electricity.
c. What is the source of electricity?
d. Define battery.
e. Write some uses of the cell.
f. How does dynamo produce electricity?
10. Project work.
Find an electric motor. Take help from your guardian to make a

dynamo.

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Unit

7.3 Magnetic and Non-magnetic Substance

Key terms and terminologies

1. Magnetic field: The special region around the magnet where it can pull a
magnetic substance is called a magnetic field.

2. Magnet: The substance which has its magnetic field is called a magnet.
3. Magnetism: The properties of the magnet are called magnetism.
4. Natural magnet: A natural black rock that has a magnetic field is called a

natural magnet.
5. Artificial magnet: A magnet made by humans is called an artificial magnet.
6. Magnetic substance: The substances that are attracted by a magnet are

called magnetic substances.
7. Non-magnetic substance: The substances that are not attracted by the

magnet are called non-magnetic substances.

Introduction

It is fun to play with magnet. It is a solid substance made of a mixture
of metals. It is made of molecules. All of the molecules of the magnet
face the same direction. Therefore, it can pull magnetic substances. It
can pull iron, nickel and cobalt. A magnet has a fixed region in which
its magnetic force is working. That region is called a magnetic field.
The special region around the magnet from which it can pull a
magnetic substance is
called the magnetic field.
A magnet has its strength.
It cannot pull things from
everywhere. A powerful
magnet has a wider narrow and weak magnetic field wide and powerful magnetic field
magnetic field. It can pull objects from a greater distance. A weak
magnet has a narrower magnetic field. It can pull objects from a closer
distance only. So, what is a magnet then? The substance which has a
magnetic field is called a magnet.

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Activity
Magnetic fields block harmful solar radiation. They keep
the earth safe. What is producing the magnetic fields?
Discuss with friends.

Fact file
Oxygen is a magnetic substance.

Resonable facts
Why a magnet cannot pull a nickel which is far away from
it?
The magnet cannot pull a nickel that is far away from it
because the nickel is outside its magnetic field.

Properties of the magnet
The properties of magnet are called magnetism.

Some properties of the magnet are listed below:
i. A magnet can pull magnetic substances.
ii. A magnet has a magnetic field.
iii. A magnet has a north pole and a south pole.
iv. The north pole of the magnet pushes the north pole of another

magnet but pulls the south pole.
v. A magnet cannot pull non-magnetic substances.

a freely suspended magnet rest in N-S like poles repel and unlike poles attracts

direction

fig: properties of magnet

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Activity
Tie a thread around the middle of a bar of magnet and
hang it freely. In which direction do its ends point?
Observe.

There are two types of magnets. They are natural magnets and
artificial magnets.

Fact file
Magnetic poles cannot be separated.

Resonable facts
Why can a magnetic compass show the direction?
A magnetic compass can show the direction because it
contains a bar magnet.

Natural magnet

A natural black rock that has a magnetic field is called a natural
magnet. Loadstone is a natural magnet. It has a weak magnetic field.

It is believed that loadstone was discovered by loadstone
a boy called Magnes. He lived in the country
of Magnesia. He was herding his sheep when
he found that the nails of his shoes were
attached to a black rock. This rock was called a
magnet. It was also called loadstone, or
lodestone, because of its ability to pull.

Artificial magnet
A magnet made by humans is called an artificial magnet. It is a
powerful magnet. Bar magnets, U-shaped magnets etc. are artificial
magnets.

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bar magnet U-shaped magnet horseshoe magnet stored in keeper

fig: artificial magnets

Magnetic substances and non-magnetic substances

We discussed that a magnet has a magnetic field. It can pull objects
within this field. But does it pull anything around it? No, it does not.
A magnet can pull an iron nail but it can never pull a paper. The
substances that are attracted by a magnet are called magnetic
substances. Some of the magnetic substances are iron, nickel and
cobalt.

iron nickel cobalt

Fig: magnetic substances

The substances that are not attracted by the magnet are called
non-magnetic substances. Paper, water and rubber are non-magnetic
substances.

paper water rubber

Fig: non-magnetic substances

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Activity
Collect an eraser, a pencil, an iron nail, a copper coin
and a plastic cup. Use a magnet to see if it is either a
magnetic or non-magnetic substance.

Fact file
Most of the power of the magnet is at its poles.

Resonable facts
Why do we use an artificial magnet in machines?
We use an artificial magnet in machines because it is
more powerful than the natural magnet.

Uses of magnet

Magnet is very useful material. It is used on many devices.

Some of the uses of the magnet are listed below:
i. Earth is a weak magnet. It blocks harmful sunlight.
ii. A bar magnet is used in a magnetic compass. The magnetic

compass shows the direction.
iii. Rocks are broken into powder. The magnet can pull metal from

the powdered rock.
iv. If an iron nail is mixed in our flour, rice, grains etc. it can be pulled

by a magnet.
v. If we lose keys, nails and needles on the ground, we can use a

magnet to find them.
vi. It is used to make generator and dynamo.
vii. It is used to make electric bells and loudspeakers.
viii. It is used to lock the refrigerator door.

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magnetic compass dynamo electric bell

fig: some devices that work by the help of magnet

Summary

1. The special region around the magnet from which it can pull a
magnetic substance is called its magnetic field.

2. The substance which has a magnetic field is called a magnet.
3. The properties of the magnet are called magnetism.
4. A magnet has a north pole and a south pole.
5. A natural black rock that has a magnetic field is called a natural

magnet.
6. A magnet made by human efforts is called an artificial magnet.
7. The substances that are attracted by a magnet are called magnetic

substances.
8. The substances that are not attracted by the magnet are called

non-magnetic substances.
9. A bar magnet is used in a magnetic compass. The magnetic

compass shows the direction.
10. If an iron nail is lost in flour, rice, or other grains, it can be

discovered by a magnet.

Model Questions with Their Answer

1. What is a magnet?
The substance which has a magnetic field is called a magnet.
2. What happens when the north pole of the magnet is brought

near the north pole of another magnet?

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If the north pole of the magnet is brought near the north pole of
another magnet, they will push each other.

3. Differentiate between magnetic and non-magnetic substances.
The differences between magnetic substances and non-magnetic

substances are:

SN Magnetic substance SN Non-magnetic substance

1 The substance that is The substance that is not

attracted by a magnet is attracted by the magnet is

called a magnetic called a non-magnetic

substance. substance.

2 It acts like a magnet when 2 It does not act like a magnet

it touches a magnet. when it touches a magnet.

Example: nickel Example: wood

4. Why is a natural magnet not used to lock the door of the fridge?

The natural magnet is not used to lock the door of the fridge
because it is very weak.

5. The magnet can pull an iron nail but cannot pull a copper nail.
What might be the reasons? Discuss in the group.

A magnet can attract an iron nail because iron is a magnetic
substance.

A magnet cannot pull a copper nail because copper is a
non-magnetic substance.

Exercise

1. Fill in the blanks with an appropriate word.

non-magnetic natural magnetic molecules powerful
magnet
field magnet

a. All of the ……….. of the magnet faces the same direction.

b. A powerful magnet has a wider …………

c. A loadstone is ………….

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d. Artificial magnet is a …………
e. Paper, water and rubber are …………. substances.

2. Write true for the correct and false for the incorrect statement.
a. Earth is a weak magnet.
b. A magnet can pull magnetic substances.
c. A magnet has a north pole and a south pole.
d. A natural black rock that has a magnetic field is called an
artificial magnet.
e. Bar magnets, U-shaped magnets etc. are natural magnets.

3. Choose the best answer from the given alternatives.

a. What is a magnet?

Object with the magnetic field Black objects Rocks None

b. Which one is an artificial magnet?

Loadstone Earth Magnetite Bar magnet

c. Which one is a natural magnet?

Loadstone U-shaped Horseshoe Bar magnet
magnet magnet

d. Which magnet is used in the compass?

Loadstone U-shaped Horseshoe Bar magnet
magnet magnet

e. Which of the following devices uses a magnet?

Electric bell Television Generator All of them

4. Match the following.

Magnetism magnetic substance

Powerful magnet loadstone

Natural magnet properties of magnet

Compass artificial magnet

Iron bar magnet

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5. Answer the following questions in a word each.
a. What is region around magnet where its power can be felt?
b. Write the name of a natural magnet.
c. Give an example of magnetic substance.
d. What is an example of non-magnetic substance?
e. Which device helps to find the direction?

6. Write any two differences between:
a. Magnetic substance and non-magnetic substance
b. Natural magnet and artificial magnet

7. Give reason.
a. A loadstone is called a natural magnet.
b. A bar magnet is an artificial magnet.
c. Nickel is a magnetic substance.
d. A paper is called a non-magnetic substance.
e. A bar magnet is used in a compass.

8. Study the given diagram and answer the following questions.
i. What is shown in the diagram?
ii. Is it powerful or not?

9. Answer the following questions.
a. What is a magnet?
b. List any three properties of a magnet.
c. What is loadstone?
d. Define magnetic substances.
e. What are non-magnetic substances?

10. Project work.

Take a small pin. Rub it in a magnet in a single direction. Put a

leaf in water. Put a nail on the leaf. What happens? Discuss in a

group.

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8UNIT Earth and Space

Introduction

The universe contains stars, planets, satellites , black holes and many
other heavenly objects. Earth is a planet. We live on it. It is our home
planet. It has three main parts: land, water and air. Living things are
found on the earth. They live in oceans, rivers, hills, valleys, plains
and deserts. Rainfall, wind, weather and the water cycle are normal
natural activities. Floods, landslides, volcanoes are some natural
disasters on the earth.

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Unit The earth
8.1

Key terms and terminologies

1. Lithosphere: The landmass present on earth is called the lithosphere.
2. Hydrosphere: The water body found on earth is called the hydrosphere.
3. Atmosphere: The layer of air around the earth is called the atmosphere.
4. Globe: Globe is a small round model of the earth.
5. Plains: The flatlands are called plains.
6. Hills: Hills are raised land surfaces.
7. Valley: The flat land surrounded by the hill is called a valley.
8. Mountain: Very tall and sloped hills are called mountains.
9. Plateau: The flatland at the top of the mountain is called a plateau.
10. Atmosphere: The layer of air around the earth is called the atmosphere.
11. Wind: Moving air is called wind.

12. Storm: A strong wind is called a storm.

Introduction

Earth is a planet because it revolves around the sun. It takes 365 days
to revolve around the sun. It is the third planet from the sun. It is the
fifth-biggest planet in the solar system. The earth is
oval. It has the North Pole and the South Pole. The
equator of earth is bulging. One day on the earth is 24
hours long. Living things can live on earth because it
has land, air and water.

The landmass present on earth is called the lithosphere. Earth

The water bodies found on earth is called the

hydrosphere. The layer of air around the earth is called the atmosphere.

Fact file
Earth’s molten iron core creates a magnetic field around
the earth.

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The globe

A globe is a very useful tool. It helps us to know globe
the actual map of the earth. A globe is a small model
of the earth. It is round. It shows the continents and
oceans. The globe is slightly tilted because our
earth itself is slightly tilted on its axis. It uses
different colours to show the different surfaces of
the earth. The blue colour represents oceans and
the green colour represents the land in the globe.

Activity
Prepare a globe. Show Nepal on the globe.

Resonable facts
Why do seasons change on the earth?
Seasons change on the earth because the axis of the
earth is tilted.

Fact file
Earth is 4.5 billion years old.

Landforms

The landmass found on the earth is not same everywhere. Earth
surface is made up of water and land. Some lands are low and some
are high. Some of the lands are fertile and some are not. There are
forests in some places. Some land has lakes, springs and rivers in it.
Some of the places have snow and ice. Water occupies 71% of the
earth's surface. Land occupies 29%.

Some of the common landforms found on earth are plains, hills,
mountains, valleys, plateaus and deserts.

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The flatlands are called plains. Terai is a plain land found in Nepal. It
is a fertile land. We can grow crops and vegetables on a fertile land. It
is covered with forest. It has enough water sources. Lakes and rivers
are found everywhere.

plain land are rich in forest crops grow well in fertile plains wet land

The hilly region of Nepal has lots of hills. Hills are raised land surfaces.
Most of it is covered with forest. Fruits grow well on hills. There can
be a flat land in the hilly region. The flat land surrounded by hills is
called a valley. Crops grow well in valleys because of the fertile soil.
Valleys have sufficient water. Springs, rivers and ponds are found in
the hills.

hills deciduous forest and ponds valley

Very tall and sloped hills are called mountains. The Himalayan region
of Nepal has lots of mountains. Mt. Sagarmatha is the tallest mountain
on the earth. Mountains are made of hard rocks. They have infertile
land. Crops do not grow well in the Himalayan regions. The forests
are thin. The flatland at the top of the mountain is called a plateau.
Snow covers the mountain. Melting snow starts rivulets. Glacial lakes
are found in this region.

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conifer forest in the glacial lakes plateau
mountains

Activity

Make a model to represent the Terai, hills and mountains
of Nepal.

Fact file
Any land that is raised 1000 feet above the surrounding
area is called a mountain.

Resonable facts
Why is it difficult to grow crops in mountain regions?
It is difficult to grow crops in the mountain region
because it has dry and infertile lands.

Atmosphere

Air surrounds the earth. The layer of air atmosphere
around the earth is called the atmosphere.
We live in the lowest layer of the
atmosphere. The atmosphere contains
various gases. Nitrogen, oxygen, water
vapour, carbon dioxide and dust particles
are found in the air. Oxygen keeps us
alive. Carbon dioxide is necessary for plants.

Fact file
The atmosphere has 5 layers. We live in the troposphere.

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Moving air is called wind. It helps in the pollination of the flower. A
strong wind is called a storm. The storm is
dangerous. It breaks trees and destroys
crops. It can kill people. We should never
go out in the storm. We should close doors
and windows and stay inside.

Mixing harmful smoke, dust and germs storm breaks trees
make the air unhealthy. We should not live

in a dirty atmosphere. Air is polluted by smoke and dust from

factories.

A range of weather activities happen in
the atmosphere. Rainfall, snowfall, clouds,
fog etc. are present in the atmosphere.

air pollution

Resonable facts
Why is the air in the city comparatively more polluted?
The air in the city is comparatively more polluted
because of the smoke from vehicles and factories.

Importance of atmosphere
i. The atmosphere blocks harmful rays from the sun.
ii. It helps to keep the earth warm.
iii. Oxygen is necessary for respiration.
iv. Plants take carbon dioxide from the air for photosynthesis.
v. Wind helps in the pollination of flowers.
vi. We can use the wind to run windmills.

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Summary

1. Rainfall, wind, weather and the water cycle are normal natural
activities.

2. The earth is oval.
3. One day on earth is 24 hours long.
4. Globe is a small model of the earth.
5. Earth surface is made up of water and land. Water occupies 71%

of the surface. The land occupies 29% of the surface.
6. The flatlands are called plains.
7. Hills are raised land surfaces.
8. The flat land surrounded by hills is called a valley.
9. Very tall and sloped hills are called mountains.
10. The flatland at the top of the mountain is called a plateau.
11. The layer of air around the earth is called the atmosphere.
12. Moving air is called the wind.
13. A strong wind is called a storm.
14. All of the weather activities occurs in the atmosphere.

Model Questions with Their Answer

1. How many hours make a day?
Twenty four hours make a day.

2. Why do plants grow well in Terai?

Plants grow well in the Terai region because it has fertile land
and enough water.

3. Differentiate between valley and mountain.
The difference between a valley and a mountain are:

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SN Valley SN Mountain

1 The flat land surrounded 1 Very tall and sloped hills

by hills is called a valley. are called mountains.

2 Soil is fertile. 2 Soil is infertile.

4. Write a short note on the structure of the earth.

The earth is an oval rock. It is not a perfect sphere. It is flat at the
north pole and the south pole. It is bulging at the equator. The
earth has flat lands called plains. It also has raised land such as
hills and mountains. There are valleys, canyons, gorges and
plateaus on earth. Some part of the earth is covered with vast
forests. Some lands are desert. There are oceans, rivers, ponds,
glaciers and waterfalls on earth.

5. Why does a Himalayan region of Nepal have a thin forest?
The mountainous region of Nepal has a thin forest because:

i. The region has infertile land.
ii. It is very cold and dry.
iii. There are not enough water sources.

Exercise

1. Fill in the blanks with an appropriate word.

atmosphere 24 globe sun oval

a. Earth is a planet because it revolves around the ………
b. The earth is ……….
c. One day on earth is ……… hours long.
d. The layer of air around the earth is called……….
e. A small model of the earth is called ………

2. Write true for the correct and false for the incorrect statement.
a. The blue colour of the globe represents land.

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b. Water occupies 71% of the earth’s surface.
c. Terai is a plain land found in Nepal.
d. A very tall and sloped hill is called a plateau.

e. Nitrogen, oxygen, water vapour, carbon dioxide and dust
particles are found in the air.

3. Choose the best answer from the given alternatives.
a. Which planet do we live on?

Mercury Venus Earth Mars
Square
b. What is the shape of the earth? Biosphere

Round Flat Oval

c. What is the landmass of the earth called?

Lithosphere Hydrosphere Atmosphere

d. What is a model of the earth called?

Map Globe Planetarium Galaxy

e. What percentage of the earth’s surface is covered by land?

71% 78% 21% 29%

4. Match the following.
The flat land layer of air around the earth
The raised lands a very strong wind
Valley hills
Storm plains
Atmosphere flat land surrounded by hills

5. Answer the following questions in a word each.

a. How many days are there in a year?

b. What is the group of water bodies found in the earth called?

c. What is a raised land with a flat top called?

d. What is the air in motion called?

e. What is a very strong and powerful wind called?

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6. Write any two differences between:
a. Atmosphere and lithosphere
b. Terai and hills
c. Valleys and mountains

7. Give reason.
a. Earth can support life.
b. Terai region of Nepal is more fertile than the mountain.
c. We should not go outside in a storm.

8. Study the given diagram and answer the following questions.
i. What is shown in the diagram?
ii. Write its advantages.
iii. How does dust mix in it?

9. Answer the following questions.
a. What is the earth?
b. What are the landforms present on the earth?
c. What are plains?
d. Define a plateau.
e. What is the atmosphere?
f. List out some importance of air.

10. Project work.

What kind of landform is your city or village? Write a short note
on that landform.

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