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CONTENTS
CONTENTS
CHAPTER
Introduction
General
E
nergy is the basic necessity for the economic development of a country
...
It is practically impossible to estimate the
actual magnitude of the part that energy has
played in the building up of present-day
civilisation
...
As a
matter of fact, there is a close relationship between the energy used per person and his standard of living
...
Energy exists in different forms in nature but
the most important form is the electrical energy
...
In this chapter, we shall
focus our attention on the general aspects of electrical energy
...
1 Importance of Electrical Energy
1
...
3 Sources of Energy
1
...
5 Units of Energy
1
...
7 Efficiency
1
...
9 Advantages of Liquid Fuels Over
Solid Fuels
1
...
1 Importance of Electrical Energy
Energy may be needed as heat, as light, as motive power etc
...
This has
given electrical energy a place of pride in the modern world
...
In fact, the advancement of a country is measured in terms of per capita consumption of
electrical energy
...
Electrical energy is a very convenient form of energy
...
For example, if we want to convert electrical energy into heat,
the only thing to be done is to pass electrical current through a wire of high resistance e
...
, a heater
...
g
...
g
...
(ii) Easy control
...
For instance, an electric motor can be started or stopped by turning on or off a switch
...
(iii) Greater flexibility
...
It can be easily transported from one place to another with the help of conductors
...
Electrical energy is much cheaper than other forms of energy
...
(v) Cleanliness
...
Therefore, its use ensures cleanliness and healthy conditions
...
The consumers of electrical energy are generally situated
quite away from the centres of its production
...
1
...
Electrical energy is a manufactured commodity like clothing, furniture or tools
...
However, electrical energy differs in one important respect
...
The entire process takes only a fraction of a second
...
Energy is available in various forms from different
natural sources such as pressure head of water, chemical
energy of fuels, nuclear energy of radioactive substances
etc
...
The
arrangement essentially employs (see Fig
...
1) an
alternator coupled to a prime mover
...
For example, chemical energy of a fuel
(e
...
, coal) can be used to produce steam at high temperature and pressure
...
The turbine converts heat energy of
steam into mechanical energy which is further converted into electrical energy by the alternator
...
1
...
Sources of Energy
Since electrical energy is produced from energy available in various forms in nature, it is desirable to
look into the various sources of energy
...
Out of these sources, the energy due to Sun and wind has not been utilised on large scale due to
a number of limitations
...
, water, fuels and nuclear energy are
primarily used for the generation of electrical energy
...
The Sun is the primary source of energy
...
This heat can be used to raise steam and
electrical energy can be produced with the help of turbine-alternator combination
...
Nevertheless, there are some locations in the world where strong solar radiation is received very
regularly and the sources of mineral fuel are scanty or lacking
...
(ii) The Wind
...
The wind energy is used to run the wind mill which drives a small generator
...
These batteries supply the energy when the wind stops
...
However, the drawbacks of this method are
(a) variable output, (b) unreliable because of uncertainty about wind pressure and (c) power generated
is quite small
...
When water is stored at a suitable place, it possesses potential energy because of the
head created
...
The water turbine drives the alternator which converts mechanical energy into electrical
energy
...
(iv) Fuels
...
, solid fuel as coal, liquid fuel as oil and gas
fuel as natural gas
...
The prime
mover drives the alternator which converts mechanical energy into electrical energy
...
Therefore, the present trend is to harness water power which is more or
less a permanent source of power
...
Towards the end of Second World War, it was discovered that large amount
of heat energy is liberated by the fission of uranium and other fissionable materials
...
The heat
produced due to nuclear fission can be utilised to raise steam with suitable arrangements
...
However,
there are some difficulties in the use of nuclear energy
...
Coal
Crude oil
Natural gas
Hydro-electric power
Nuclear power
Renewables
Energy Utilisation
1
...
Below is given their comparison in a tabular form :
S
...
Particular
Water-power
Fuels
Nuclear energy
1
...
3
...
5
...
Reliability
Most reliable
Less reliable
More reliable
1
...
The most important forms of energy are
mechanical energy, electrical energy and thermal energy
...
However, it must be realised that since mechanical, electrical and thermal energies
are interchangeable, it is possible to assign the same unit to them
...
6
...
The unit of mechanical energy is newton-metre or joule on the M
...
S
...
The work done on a body is one newton-metre (or joule) if a force of one newton moves it
through a distance of one metre i
...
,
Mechanical energy in joules = Force in newton × distance in metres
(ii) Electrical energy
...
d
...
e
...
In practice, for
the measurement of electrical energy, bigger units viz
...
1 watt-hour = 1 watt × 1 hr
= 1 watt × 3600 sec = 3600 watt-sec
5
1 kilowatt hour (kWh) = 1 kW × 1 hr = 1000 watt × 3600 sec = 36 x 10 watt-sec
...
Heat is a form of energy which produces the sensation of warmth
...
Th
...
) and centigrade heat units (C
...
U
...
Calorie
...
e
...
A kilocalorie is the amount of heat required
to raise the temperature of 1 kg of water through 1ºC i
...
,
1 kilocalorie = 1 kg × 1ºC = 1000 gm × 1ºC = 1000 calories
B
...
U
...
e
...
Th
...
= 1 lb × 1ºF
C
...
U
...
e
...
H
...
= 1 lb × 1ºC
1
...
e
...
Therefore, mechanical, electrical and thermal
energies must have the same unit
...
It will be seen that these units are related to
each other by some constant
...
or Joules
5
∴
1 kWh = 36 × 10 Joules
It is clear that electrical energy can be expressed in Joules instead of kWh
...
H
...
= 1 lb × 1ºC = 453·6 gm × 1ºC
= 453·6 calories = 453·6 × 4·18 Joules = 1896 Joules
∴
1C
...
U
...
Th
...
= 1 lb × 1ºF = 453·6 gm × 5/9 ºC
= 252 calories = 252 × 4·18 Joules = 1053 Joules
∴
1 B
...
U
...
calorie,
B
...
U
...
H
...
*
The SI or MKS unit of thermal energy being used these days is the joule—exactly as for mechanical and
electrical energies
...
calorie, B
...
U
...
H
...
are obsolete
...
H
...
= 1898 C
...
U
...
H
...
= 1896 Joules]
1 kWh = 1898 C
...
U
...
Th
...
= 3418 B
...
U
...
Th
...
= 1053 Joules]
5
∴
1 kWh = 3418 B
...
U
...
This is expected since electrical and thermal energies are interchangeable
...
7 Efficiency
Energy is available in various
forms from different natural
sources such as pressure head
of water, chemical energy of
fuels, nuclear energy of
radioactive substances etc
...
In this process
of conversion, some energy is
lost in the sense that it is
converted to a form different
from electrical energy
...
The
output energy divided by the
input energy is called energy
efficiency or simply efficiency
of the system
...
Output energy
Input energy
As power is the rate of energy flow, therefore, efficiency may be expressed equally well as output
power divided by input power i
...
,
Output power
Efficiency, η =
Input power
Efficiency, η =
Example 1
...
Mechanical energy is supplied to a d
...
generator at the rate of 4200 J/s
...
(i) What is the percentage efficiency of the generator ?
(ii) How much energy is lost per minute of operation ?
Introduction
7
Solution
...
In other words, every system is less than
100 % efficient
...
8 Calorific Value of Fuels
The amount of heat produced by the complete combustion of a unit weight of fuel is known as its
calorific value
...
The greater the calorific value
of fuel, the larger is its ability to produce heat
...
However, in case of gaseous fuels, it is generally stated in cal/litre or
kcal/litre
...
S
...
Particular
1
...
3
...
9 Advantages of Liquid Fuels over Solid Fuels
The following are the advantages of liquid fuels over the solid fuels :
(i) The handling of liquid fuels is easier and they require less storage space
...
(iii) The solid fuels have higher percentage of moisture and consequently they burn with great
difficulty
...
(iv) The waste product of solid fuels is a large quantity of ash and its disposal becomes a problem
...
(v) The firing of liquid fuels can be easily controlled
...
1
...
Liquids fuels are costlier as compared to solid fuels
...
Liquid fuels require special types of burners for burning
...
SELF-TEST
1
...
(i) The primary source of energy is the
...
(iii) 1 kWh =
...
(v) The three principal sources of energy used for the generation of electrical energy are
...
2
...
(i) Electrical energy is
...
(cheaper, costlier)
(ii) The electrical, heat and mechanical energies
...
(can, cannot)
(iii)
...
(fuels, radioactive substances, water)
(iv) The basic unit of energy is
...
into
...
(i) Sun, (ii) electrical energy, (iii) 860, (iv) cal/gm or kcal/kg, (v) water, fuels and radioactive substances
...
(i) Cheaper, (ii) can, (iii) fuels, (iv) Joule, (v) mechanical energy, electrical energy
...
2
...
4
...
Why is electrical energy preferred over other forms of energy ?
Write a short note on the generation of electrical energy
...
Compare the chief sources of energy used for the generation of electrical energy
...
Th
...
= 1053 Joules
(iv) 1 C
...
U
...
What do you mean by efficiency of a system ?
7
...
What are the advantages of solid fuels over the liquid fuels ?
DISCUSSION QUESTIONS
1
...
3
...
5
...
What is the principal source of generation of electrical energy ?
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