NCERT Textbook - Sources of Energy Class 10 Notes | EduRev

Science & Technology for UPSC CSE

Class 10 : NCERT Textbook - Sources of Energy Class 10 Notes | EduRev

 Page 1


Science
242
Sources of
Energy
14 CHAPTER
I
n Class IX, we learnt that the total energy during a physical or chemical
process is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.
14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHAT IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1
n List four forms of energy that you use from morning, when you
wake up, till you reach the school.
n From where do we get these different forms of energy?
n Can we call these ‘sources’ of energy? Why or why not?
2020-21
Page 2


Science
242
Sources of
Energy
14 CHAPTER
I
n Class IX, we learnt that the total energy during a physical or chemical
process is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.
14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHAT IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1
n List four forms of energy that you use from morning, when you
wake up, till you reach the school.
n From where do we get these different forms of energy?
n Can we call these ‘sources’ of energy? Why or why not?
2020-21
Sources of Energy 243
The muscular energy for carrying out physical work, electrical energy
for running various appliances, chemical energy for cooking food or
running a vehicle all come from some source. We need to know how do
we select the source needed for obtaining the energy in its usable form.
Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2
n Consider the various options we have when we choose a fuel for
cooking our food.
n What are the criteria you would consider when trying to categorise
something as a good fuel?
n Would your choice be different if you lived
(a) in a forest?
(b) in a remote mountain village or small island?
(c) in New Delhi?
(d) lived five centuries ago?
n How are the factors different in each case?
After going through the two activities above, we can see that the
particular source of energy, or fuel, we select for performing some work
depends on many different factors. For example, while selecting a fuel,
we would ask ourselves the following questions.
(i) How much heat does it release on burning?
(ii) Does it produce a lot of smoke?
(iii) Is it easily available?
Can you think of three more relevant questions to ask about a fuel?
Given the range of fuels we have today, what are the factors which
would limit our choices when it comes to a particular task like cooking
our food? Would the fuel selected also depend on the work to be done?
For example, would we choose one fuel for cooking and another for
heating the room in winter?
We could then say that a good source of energy would be one
n which would do a large amount of work per unit volume or mass,
n be easily accessible,
n be easy to store and transport, and
n perhaps most importantly, be economical.
QUESTIONS
?
1. What is a good source of energy?
2. What is a good fuel?
3. If you could use any source of energy for heating your food, which one
would you use and why?
2020-21
Page 3


Science
242
Sources of
Energy
14 CHAPTER
I
n Class IX, we learnt that the total energy during a physical or chemical
process is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.
14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHAT IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1
n List four forms of energy that you use from morning, when you
wake up, till you reach the school.
n From where do we get these different forms of energy?
n Can we call these ‘sources’ of energy? Why or why not?
2020-21
Sources of Energy 243
The muscular energy for carrying out physical work, electrical energy
for running various appliances, chemical energy for cooking food or
running a vehicle all come from some source. We need to know how do
we select the source needed for obtaining the energy in its usable form.
Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2
n Consider the various options we have when we choose a fuel for
cooking our food.
n What are the criteria you would consider when trying to categorise
something as a good fuel?
n Would your choice be different if you lived
(a) in a forest?
(b) in a remote mountain village or small island?
(c) in New Delhi?
(d) lived five centuries ago?
n How are the factors different in each case?
After going through the two activities above, we can see that the
particular source of energy, or fuel, we select for performing some work
depends on many different factors. For example, while selecting a fuel,
we would ask ourselves the following questions.
(i) How much heat does it release on burning?
(ii) Does it produce a lot of smoke?
(iii) Is it easily available?
Can you think of three more relevant questions to ask about a fuel?
Given the range of fuels we have today, what are the factors which
would limit our choices when it comes to a particular task like cooking
our food? Would the fuel selected also depend on the work to be done?
For example, would we choose one fuel for cooking and another for
heating the room in winter?
We could then say that a good source of energy would be one
n which would do a large amount of work per unit volume or mass,
n be easily accessible,
n be easy to store and transport, and
n perhaps most importantly, be economical.
QUESTIONS
?
1. What is a good source of energy?
2. What is a good fuel?
3. If you could use any source of energy for heating your food, which one
would you use and why?
2020-21
Science
244
14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY
14.2.1 Fossil Fuels
In ancient times, wood was the most common source of heat energy. The
energy of flowing water and wind was also used for limited activities. Can
you think of some of these uses? The exploitation of coal as a source of
energy made the industrial revolution possible. Increasing
industrialisation has led to a better quality of life all over the world. It has
also caused the global demand for energy to grow at a tremendous rate.
The growing demand for energy was largely met by the fossil fuels – coal
and petroleum. Our technologies were also developed for using these
energy sources. But these fuels were formed over millions of years ago
and there are only limited reserves. The fossil fuels are non-renewable
sources of energy, so we need to conserve
them. If we were to continue consuming these
sources at such alarming rates, we would
soon run out of energy! In order to avoid this,
alternate sources of energy were explored.
But we continue to be largely dependent on
fossil fuels for most of our energy
requirements (Fig. 14.1).
Burning fossil fuels has other disadvantages too. We learnt in Class IX
about the air pollution caused by burning of coal or petroleum products.
The oxides of carbon, nitrogen and sulphur that are released on burning
fossil fuels are acidic oxides. These lead to acid rain which affects our
water and soil resources. In addition to the problem of air pollution,
recall the green-house effect of gases like carbon dioxide.
Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1
Pie-chart showing the
major sources of energy
for our requirements in
India
The pollution caused by burning fossil fuels can be somewhat reduced
by increasing the efficiency of the combustion process and using various
techniques to reduce the escape of harmful gases and ashes into the
surroundings. Besides being used directly for various purposes – in gas
stoves and vehicles, do you know fossil fuels are the major fuels used for
generating electricity? Let us produce some electricity at our own small
plant in the class and see what goes into producing our favourite form
of energy.
Think it over
How would our lives change if we could no longer get electricity supply?
The availability of electrical energy to each individual in a country is one of the
parameters to measure the growth of the country.
Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3
n Take a table-tennis ball and make three slits into it.
n Put semicircular ( ) fins cut out of a metal sheet into these slits.
n Pivot the tennis ball on an axle through its centre with a straight
metal wire fixed to a rigid support. Ensure that the tennis ball
rotates freely about the axle.
2020-21
Page 4


Science
242
Sources of
Energy
14 CHAPTER
I
n Class IX, we learnt that the total energy during a physical or chemical
process is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.
14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHAT IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1
n List four forms of energy that you use from morning, when you
wake up, till you reach the school.
n From where do we get these different forms of energy?
n Can we call these ‘sources’ of energy? Why or why not?
2020-21
Sources of Energy 243
The muscular energy for carrying out physical work, electrical energy
for running various appliances, chemical energy for cooking food or
running a vehicle all come from some source. We need to know how do
we select the source needed for obtaining the energy in its usable form.
Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2
n Consider the various options we have when we choose a fuel for
cooking our food.
n What are the criteria you would consider when trying to categorise
something as a good fuel?
n Would your choice be different if you lived
(a) in a forest?
(b) in a remote mountain village or small island?
(c) in New Delhi?
(d) lived five centuries ago?
n How are the factors different in each case?
After going through the two activities above, we can see that the
particular source of energy, or fuel, we select for performing some work
depends on many different factors. For example, while selecting a fuel,
we would ask ourselves the following questions.
(i) How much heat does it release on burning?
(ii) Does it produce a lot of smoke?
(iii) Is it easily available?
Can you think of three more relevant questions to ask about a fuel?
Given the range of fuels we have today, what are the factors which
would limit our choices when it comes to a particular task like cooking
our food? Would the fuel selected also depend on the work to be done?
For example, would we choose one fuel for cooking and another for
heating the room in winter?
We could then say that a good source of energy would be one
n which would do a large amount of work per unit volume or mass,
n be easily accessible,
n be easy to store and transport, and
n perhaps most importantly, be economical.
QUESTIONS
?
1. What is a good source of energy?
2. What is a good fuel?
3. If you could use any source of energy for heating your food, which one
would you use and why?
2020-21
Science
244
14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY
14.2.1 Fossil Fuels
In ancient times, wood was the most common source of heat energy. The
energy of flowing water and wind was also used for limited activities. Can
you think of some of these uses? The exploitation of coal as a source of
energy made the industrial revolution possible. Increasing
industrialisation has led to a better quality of life all over the world. It has
also caused the global demand for energy to grow at a tremendous rate.
The growing demand for energy was largely met by the fossil fuels – coal
and petroleum. Our technologies were also developed for using these
energy sources. But these fuels were formed over millions of years ago
and there are only limited reserves. The fossil fuels are non-renewable
sources of energy, so we need to conserve
them. If we were to continue consuming these
sources at such alarming rates, we would
soon run out of energy! In order to avoid this,
alternate sources of energy were explored.
But we continue to be largely dependent on
fossil fuels for most of our energy
requirements (Fig. 14.1).
Burning fossil fuels has other disadvantages too. We learnt in Class IX
about the air pollution caused by burning of coal or petroleum products.
The oxides of carbon, nitrogen and sulphur that are released on burning
fossil fuels are acidic oxides. These lead to acid rain which affects our
water and soil resources. In addition to the problem of air pollution,
recall the green-house effect of gases like carbon dioxide.
Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1
Pie-chart showing the
major sources of energy
for our requirements in
India
The pollution caused by burning fossil fuels can be somewhat reduced
by increasing the efficiency of the combustion process and using various
techniques to reduce the escape of harmful gases and ashes into the
surroundings. Besides being used directly for various purposes – in gas
stoves and vehicles, do you know fossil fuels are the major fuels used for
generating electricity? Let us produce some electricity at our own small
plant in the class and see what goes into producing our favourite form
of energy.
Think it over
How would our lives change if we could no longer get electricity supply?
The availability of electrical energy to each individual in a country is one of the
parameters to measure the growth of the country.
Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3
n Take a table-tennis ball and make three slits into it.
n Put semicircular ( ) fins cut out of a metal sheet into these slits.
n Pivot the tennis ball on an axle through its centre with a straight
metal wire fixed to a rigid support. Ensure that the tennis ball
rotates freely about the axle.
2020-21
Sources of Energy 245
n Now connect a cycle dynamo to this.
n Connect a bulb in series.
n Direct a jet of water or steam produced in a pressure cooker at the
fins (Fig. 14.2). What do you observe?
This is our turbine for generating electricity. The simplest turbines
have one moving part, a rotor-blade assembly. The moving fluid acts on
the blades to spin them and impart energy to the rotor. Thus, we see
that basically we need to move the fan, the rotor blade, with speed which
would turn the shaft of the dynamo and convert the mechanical energy
into electrical energy — the form of energy which has become a necessity
in today’s scenario. The various ways in which this can be done depends
upon availability of the resources. We will see how various sources of
energy can be harnessed to run the turbine and generate electricity in
the following sections.
14.2.2 Thermal Power Plant
Large amount of fossil fuels are burnt every day in power stations to
heat up water to produce steam which further runs the turbine to
generate electricity. The transmission of electricity is more efficient than
transporting coal or petroleum over the same distance. Therefore, many
thermal power plants are set up near coal or oil fields. The term thermal
power plant is used since fuel is burnt to produce heat energy which is
converted into electrical energy.
14.2.3 Hydro Power Plants
Another traditional source of energy was the kinetic energy of flowing
water or the potential energy of water at a height. Hydro power plants
convert the potential energy of falling water into electricity. Since there
are very few water-falls which could be used as a source of potential
energy, hydro power plants are associated with dams. In the last century,
a large number of dams were built all over the world. As we can see from
Fig. 14.1, a quarter of our energy requirement in India is met by hydro
power plants.
Figure 14.2 Figure 14.2 Figure 14.2 Figure 14.2 Figure 14.2 A model to demonstrate the process of thermoelectric production
2020-21
Page 5


Science
242
Sources of
Energy
14 CHAPTER
I
n Class IX, we learnt that the total energy during a physical or chemical
process is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.
14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHA 14.1 WHAT IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY? T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1 Activity 14.1
n List four forms of energy that you use from morning, when you
wake up, till you reach the school.
n From where do we get these different forms of energy?
n Can we call these ‘sources’ of energy? Why or why not?
2020-21
Sources of Energy 243
The muscular energy for carrying out physical work, electrical energy
for running various appliances, chemical energy for cooking food or
running a vehicle all come from some source. We need to know how do
we select the source needed for obtaining the energy in its usable form.
Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2 Activity 14.2
n Consider the various options we have when we choose a fuel for
cooking our food.
n What are the criteria you would consider when trying to categorise
something as a good fuel?
n Would your choice be different if you lived
(a) in a forest?
(b) in a remote mountain village or small island?
(c) in New Delhi?
(d) lived five centuries ago?
n How are the factors different in each case?
After going through the two activities above, we can see that the
particular source of energy, or fuel, we select for performing some work
depends on many different factors. For example, while selecting a fuel,
we would ask ourselves the following questions.
(i) How much heat does it release on burning?
(ii) Does it produce a lot of smoke?
(iii) Is it easily available?
Can you think of three more relevant questions to ask about a fuel?
Given the range of fuels we have today, what are the factors which
would limit our choices when it comes to a particular task like cooking
our food? Would the fuel selected also depend on the work to be done?
For example, would we choose one fuel for cooking and another for
heating the room in winter?
We could then say that a good source of energy would be one
n which would do a large amount of work per unit volume or mass,
n be easily accessible,
n be easy to store and transport, and
n perhaps most importantly, be economical.
QUESTIONS
?
1. What is a good source of energy?
2. What is a good fuel?
3. If you could use any source of energy for heating your food, which one
would you use and why?
2020-21
Science
244
14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY 14.2 CONVENTIONAL SOURCES OF ENERGY
14.2.1 Fossil Fuels
In ancient times, wood was the most common source of heat energy. The
energy of flowing water and wind was also used for limited activities. Can
you think of some of these uses? The exploitation of coal as a source of
energy made the industrial revolution possible. Increasing
industrialisation has led to a better quality of life all over the world. It has
also caused the global demand for energy to grow at a tremendous rate.
The growing demand for energy was largely met by the fossil fuels – coal
and petroleum. Our technologies were also developed for using these
energy sources. But these fuels were formed over millions of years ago
and there are only limited reserves. The fossil fuels are non-renewable
sources of energy, so we need to conserve
them. If we were to continue consuming these
sources at such alarming rates, we would
soon run out of energy! In order to avoid this,
alternate sources of energy were explored.
But we continue to be largely dependent on
fossil fuels for most of our energy
requirements (Fig. 14.1).
Burning fossil fuels has other disadvantages too. We learnt in Class IX
about the air pollution caused by burning of coal or petroleum products.
The oxides of carbon, nitrogen and sulphur that are released on burning
fossil fuels are acidic oxides. These lead to acid rain which affects our
water and soil resources. In addition to the problem of air pollution,
recall the green-house effect of gases like carbon dioxide.
Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1 Figure 14.1
Pie-chart showing the
major sources of energy
for our requirements in
India
The pollution caused by burning fossil fuels can be somewhat reduced
by increasing the efficiency of the combustion process and using various
techniques to reduce the escape of harmful gases and ashes into the
surroundings. Besides being used directly for various purposes – in gas
stoves and vehicles, do you know fossil fuels are the major fuels used for
generating electricity? Let us produce some electricity at our own small
plant in the class and see what goes into producing our favourite form
of energy.
Think it over
How would our lives change if we could no longer get electricity supply?
The availability of electrical energy to each individual in a country is one of the
parameters to measure the growth of the country.
Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3 Activity 14.3
n Take a table-tennis ball and make three slits into it.
n Put semicircular ( ) fins cut out of a metal sheet into these slits.
n Pivot the tennis ball on an axle through its centre with a straight
metal wire fixed to a rigid support. Ensure that the tennis ball
rotates freely about the axle.
2020-21
Sources of Energy 245
n Now connect a cycle dynamo to this.
n Connect a bulb in series.
n Direct a jet of water or steam produced in a pressure cooker at the
fins (Fig. 14.2). What do you observe?
This is our turbine for generating electricity. The simplest turbines
have one moving part, a rotor-blade assembly. The moving fluid acts on
the blades to spin them and impart energy to the rotor. Thus, we see
that basically we need to move the fan, the rotor blade, with speed which
would turn the shaft of the dynamo and convert the mechanical energy
into electrical energy — the form of energy which has become a necessity
in today’s scenario. The various ways in which this can be done depends
upon availability of the resources. We will see how various sources of
energy can be harnessed to run the turbine and generate electricity in
the following sections.
14.2.2 Thermal Power Plant
Large amount of fossil fuels are burnt every day in power stations to
heat up water to produce steam which further runs the turbine to
generate electricity. The transmission of electricity is more efficient than
transporting coal or petroleum over the same distance. Therefore, many
thermal power plants are set up near coal or oil fields. The term thermal
power plant is used since fuel is burnt to produce heat energy which is
converted into electrical energy.
14.2.3 Hydro Power Plants
Another traditional source of energy was the kinetic energy of flowing
water or the potential energy of water at a height. Hydro power plants
convert the potential energy of falling water into electricity. Since there
are very few water-falls which could be used as a source of potential
energy, hydro power plants are associated with dams. In the last century,
a large number of dams were built all over the world. As we can see from
Fig. 14.1, a quarter of our energy requirement in India is met by hydro
power plants.
Figure 14.2 Figure 14.2 Figure 14.2 Figure 14.2 Figure 14.2 A model to demonstrate the process of thermoelectric production
2020-21
Science
246
In order to produce hydel electricity,
high-rise dams are constructed on the river
to obstruct the flow of water and thereby
collect water in larger reservoirs. The water
level rises and in this process the kinetic
energy of flowing water gets transformed into
potential energy. The water from the high
level in the dam is carried through pipes, to
the turbine, at the bottom of the dam
(Fig. 14.3). Since the water in the reservoir
would be refilled each time it rains (hydro
power is a renewable source of energy) we
would not have to worry about hydro
electricity sources getting used up the way
fossil fuels would get finished one day.
But, constructions of big dams have certain problems associated
with it. The dams can be constructed only in a limited number of places,
preferably in hilly terrains. Large areas of agricultural land and human
habitation are to be sacrificed as they get submerged. Large eco-systems
are destroyed when submerged under the water in dams. The vegetation
which is submerged rots under anaerobic conditions and gives rise to
large amounts of methane which is also a green-house gas. It creates
the problem of satisfactory rehabilitation of displaced people. Opposition
to the construction of Tehri Dam on the river Ganga and Sardar Sarovar
project on the river Narmada are due to such problems.
14.2.4 Improvements in the Technology for using
Conventional Sources of Energy
Bio-Mass
We mentioned earlier that wood has been used as a fuel for a long time.
If we can ensure that enough trees are planted, a continuous supply of
fire-wood can be assured. You must also be familiar with the use of
cow-dung cakes as a fuel. Given the large live-stock population in India,
this can also assure us a steady source of fuel. Since these fuels are
plant and animal products, the source of these fuels is said to be
bio-mass. These fuels, however, do not produce much heat on burning
and a lot of smoke is given out when they are burnt. Therefore,
technological inputs to improve the efficiency of these fuels are necessary.
When wood is burnt in a limited supply of oxygen, water and volatile
materials present in it get removed and charcoal is left behind as the
residue. Charcoal burns without flames, is comparatively smokeless and
has a higher heat generation efficiency.
Similarly, cow-dung, various plant materials like the residue after
harvesting the crops, vegetable waste and sewage are decomposed in
the absence of oxygen to give bio-gas. Since the starting material is mainly
cow-dung, it is popularly known as ‘gobar-gas’. Bio-gas is produced in
a plant as shown in Fig. 14.4.
Figure 14.3 Figure 14.3 Figure 14.3 Figure 14.3 Figure 14.3
A schematic view of a
hydro power plant
2020-21
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