SOURCES
OF ENERGY
GOOD
/IDEAL SOURCE OF ENERGY
What is a good fuel?
Answer:- A good fuel
produces a huge amount of heat on burning, does not produce a lot of smoke, and
is easily available
What is a good source
of energy? OR What are the qualities of
an ideal source of energy?
Answer :-A good source
of energy fulfils the following criteria:
(I)It produces a lot
of heat per unit mass. and energy on burning
(II) It does a huge
amount of work per unit mass.
(III) It is easily
accessible.
(IV) It is easy to store
and transport.
(V)It is economical.
If you could use any
source of energy for heating your food, which one would you use and why?
Answer :-Natural gas
can be used for heating and cooking food because it is a clean source of
energy. It does not produce huge amount of smoke on burning. Although it is
highly inflammable, it is easy to use, transport, and it produces a huge amount
of heat on burninG.
FOSSIL
FUELS
Energy resources are
two types:
• Conventional sources
• Non-conventional sources
Conventional sources
of energy include fossil fuels, thermal energy and hydroelectric energy.
FossilFuels
It includes fuels
which are most commonly used such as wood, coal and petroleum. These fossil fuels
are non-renewable sources of energy. Therefore we need to conserve them.
Wood
•It is a major source
of energy for man as it is widely used for cooking and heating
•It is a primary fuel
which can be used directly to produce heat
Disadvantages
•A major portion of
heat produced by burning wood is lost to the surroundings and only 8% of the
total heat is actually used for cooking food leading to huge wastage of fuel
•It produces a lot of
smoke due to incomplete combustion leading to pollution and health hazards
Coal
•Coal varies in
quality according to the amount of pressure and heat to which it is subjected
to during its formation
•It consists largely
of carbon, hydrogen, oxygen and a small amount of sulphur and nitrogen
•It is formed in
layers called seams and takes millions of years to be formed
Disadvantages
• The oxides of carbon, nitrogen and
sulphur are released on burning coal and petroleum which are acidic oxides.
Thus, they lead to acid rain which affects our water and soil resources
NOTE POINTS:-
The remains of plant
and animals buried under the earth millions of years ago are known as fossils.
These fossils are excellent fuels and are called fossil fuels. The common
examples of fusil fuels are coal, petroleum and natural gas.
What are the
disadvantages of fossil fuels?
Answer
The disadvantages of
fossil fuels are as follows:
(a) Burning of coal
and petroleum produces a lot of pollutants causing air pollution.
(b) Fossil fuels
release oxides of carbon, nitrogen, sulphur, etc. that cause acid rain, which
affects the soil fertility and potable water.
(c) Burning of fossil
fuels produce gases such as carbon dioxide that causes global warming.
Question Why are we
looking at alternate sources of energy?
Answer Fossil fuels,
which have been traditionally used by human beings as an energy sources, are
non-renewable sources of energy. These sources of energy are limited and cannot
replenish on their own. They are being consumed at a large rate. If this rate
of consumption continues, then the fossil fuels would be exhausted from the
Earth. Therefore, we have to conserve the energy sources. Hence, we should look
for alternate sources of energy.
Question How has the
traditional use of wind and water energy been modified for our convenience?
Answer Traditionally,
waterfalls were used as a source of potential energy which was converted to
electricity with the help of turbines. Since waterfalls are few in number,
water dams have been constructed in large numbers. Nowadays, hydro-dams are
used in order to harness potential energy of stored water. In water dams, water
falls from a height on the turbine, which produces electricity.
Earlier, the windmills
were used to harness wind energy to do mechanical work such as lifting/drawing
water from a well. Today, windmills are used to generate electricity. In
windmills, the kinetic energy of wind is harnessed and converted into
electricity. The rotatory motion of the blades turns the turbine of the
electric generator to generate electricity.
HYDROPOWER PLANTS
The energy of flowing
water is utilised to produce electricity on a large scale at hydroelectric
power plants. This is another conventional source of energy derived from
flowing water. Dams are constructed across the waterfalls to derive electrical
energy from it.
Principle:-The
water flowing in a river is collected by constructing a high rise dam. This
stored water is then allowed to fall from the top of the reservoir on to a
water turbine located at the bottom of the dam. The fast moving water rotates
the blades of the water turbine, which in turn rotates the armature of the
generator and produces electricity.
Construction
and Working
Water flowing in high
altitude rivers is stored in a man-made reservoir as shown in the figure. The
kinetic energy of the flowing water is transformed into potential energy as the
water level rises. This water is carried through pipes to the turbine situated
at the bottom of the dam. The water turbine has cup-shaped discs around its
circumference. A jet of moving water rotates the water turbine rapidly which in
turn rotates the shaft which is attached to its centre. The other end of the
shaft is connected to the coil of an electric generator. The generator coil
rotates and produces electricity.
It has been estimated
that the total hydroelectric power potential in India is about 4 x 1011
kilowatt-hours but only 11% of this total potential has been utilized so far.
Advantages of Hydroelectricity
The generation of
electricity from water does not produce any environmental pollution
• Water is a renewable source of energy
• The construction of dams on rivers
helps in controlling floods and also helps in irrigation
BIOGAS
Biogas is a clean and
efficient fuel. It is a mixture of methane (CH4), carbon dioxide (CO2),
hydrogen (H2) and hydrogen sulphide (H2S).
The chief constituent
of biogas is methane (upto 75%).
Production of Biogas -
Fixed Dome Type Biogas Plant
Raw Materials Required
Forms of biomass
listed below may be used along with water:
• Animal dung
• Poultry wastes
• Plant wastes ( Husk, grass, weeds
etc.)
• Human excreta
• Industrial wastes(Saw dust, wastes
from food processing industries)
• Domestic wastes (Vegetable peels,
waste food materials)
Principle:-Biogas is produced as a result of anaerobic fermentation of biomass in the presence of water.
Construction
The biogas plant is a
brick and cement structure having the following five sections:
• Mixing tank present above the ground
level
• Inlet chamber: The mixing tank opens
underground into a sloping inlet chamber
• Digester: The inlet chamber opens
from below into the digester which is a huge tank with a dome like ceiling. The
ceiling of the digester has an outlet with a valve for the supply of biogas
• Outlet chamber: The digester opens
from below into an outlet chamber
• Overflow tank: The outlet chamber
opens from the top into a small over flow tank
Working
• The various forms of biomass are
mixed with an equal quantity of water in the mixing tank. This forms the slurry
• The slurry is fed into the digester
through the inlet chamber. The temperature of the slurry must be maintained
around 35 oC. Any drop in temperature will reduce the anaerobic activity and
hence the yield of biogas
• When the digester is partially filled
with the slurry, the introduction of slurry is stopped and the plant is left
unused for about two months
• During these two months, anaerobic
bacteria present in the slurry decompose or ferment the biomass in the presence
of water
• As a result of anaerobic
fermentation, biogas is formed, which starts collecting in the dome of the
digester
• As more and more biogas starts
collecting, the pressure exerted by the biogas forces the spent slurry into the
outlet chamber
• From the outlet chamber, the spent
slurry overflows into the overflow tank
• The spent slurry is manually removed
from the overflow tank and used as manure for plants
• The gas valve connected to a system
of pipelines is opened when a supply of biogas is required
• To obtain a continuous supply of
biogas, a functioning plant can be fed continuously with the prepared slurry
•
Advantages
of Fixed Dome Type of Biogas Plant
• Requires only locally and easily
available materials for construction
• Inexpensive
• Easy to construct
• Due to the above reasons, this plant
is also called the Janata Gobar gas plant.
Advantages
of Biogas as a Fuel
• As domestic fuel
• For street lighting
• For generation of electricity
• High calorific value
• Clean and excellent fuel containing
upto 75% methane
• No residue produced
• No smoke produced
• Non - polluting
• The slurry is periodically removed
and used as excellent manure which is rich in nitrogen and phosphorous
• Economical
• Can be supplied through pipe lines
• Burns readily - has a convenient
ignition temperature
Advantages of Biogas
Plants
o Reduces burden on forests and fossil
fuels
o Produces a clean fuel - helps in
controlling air pollution
o Provides nutrient rich (N & P)
manure for plants
o Controls water pollution by
decomposing sewage, animal dung and human excreta
Limitations of Biogas
Plants
o Initial cost of installation of the
plant being high, and is beyond the reach of an average rural Indian
o Number of cattle owned by an average
family of farmers is inadequate to feed a biogas plant
WIND ENERGY
1. A windmill is a simple machine that
works with the energy of the wind. The windmill can be used to run a pump to
draw water from the ground. It can also be used to run a flour mill to grind
grain.
NOTE POINTS:-
2. The moving water also possesses kinetic
energy. The water – wheel is a device used for obtaining energy from flowing
water.
3. The energy of naturally flowing water
in high rivers is generally stored behind dams as potential energy and then
further used to generate electricity. The electricity produced by using the
energy of flowing water is known as hydro – electric power. The most important
advantage of water energy is that like wind energy, it does not cause any
pollution.
Moving air is called
wind and it possesses Kinetic energy. In the earlier days, it was utilized by
man in winnowing to remove husk from grains, in propelling sail boats in rivers
and seas for transport purposes. But nowadays this wind energy is used to
produce electricity.
What Causes Wind to
Blow?
Solar energy is
responsible for the blowing of wind. The intensity of sun-rays is stronger near
the Equator than at the Polar Regions. Due to unequal heating of the earth's
surface, cooler air from the Polar Regions flow towards the equatorial regions
to fill the space created by the hot rising air. Air flows from high pressure
region to low pressure region. This flow of air from one place to another
constitutes wind.
The energy of wind is
used for working of flour-mills and water-lifting pumps with an electric
generator. Such simple machines which work due to kinetic energy of wind are
called wind mills.
The Principle of
Windmill
When the blowing wind
strikes across the blades of a windmill, it exerts a force on them due to which
the blades of the windmill start rotating. This in turn rotates the shaft of
the turbine and generates electricity.
Working
of the Windmill
Wind turbines are used
to produce electricity. The machines that generate electricity are the most
conventional type with airfoil propeller employing two to three tapered blades.
Electricity can be produced by rotating an armature in between the poles of a
strong magnet. The shaft of the armature of a generator is connected to the
wind turbine by a connecting rod. When the wind rotates the blades of the wind
turbine, the shaft rotates, and this in turn rotates the armature, thereby
producing electricity.
The wind speed should
be higher than 15 km/h to maintain the required speed of the turbine.
Advantages of Wind
Energy
One advantage of wind
energy is that it is available everywhere and in plenty. We will never run out
of wind power. It does not create any kind of pollution; like smoke and harmful
gases or harmful radiations.
Limitations of Wind
Energy
Even though wind
energy is available in plenty, wind is not available at all times. It is
unpredictable and not dependable. Hence to produce maximum amount of energy
from wind, wind energy maps are prepared, which give us an idea of the average
wind speed throughout the year at different places. The maps give annual
average, average for January (a typical low wind month) and an average for July
(a typical windy month). The maps also provide information about energy
available in one square meter of a wind stream at about 10 m high above the
ground level.
For large scale
production, a 'wind farm' with a hundred or more wind turbines is needed. The
turbines must be sited in windy areas which are often the most attractive parts
of the landscape.
The energy output of
each windmill in a farm is coupled together to get electricity on a commercial
scale.
The wind power
potential of our country is estimated to be about 45,000 MW. At present we are
able to generate 380 MW of electricity from the largest wind energy farm
established near Kanyakumari in Tamil Nadu. India ranks fifth in harnessing
wind energy for the production of electricity.
We shall discuss each
non-conventional source of energy in detail.
The Solar Energy
Sunlight falling on
the earth's surface equals 50,000 times the energy used each year by man.
Almost all our energy comes from sun.
The sun's energy is
responsible for the tidal energy, heat energy stored in water, the chemical
energy stored in plants, and the kinetic energy stored in the wind, from which
we can obtain electrical energy. This is the indirect use of solar energy. We
can also harness solar energy directly. Solar water heater and solar cells
directly harness solar energy.
Only a small part of
the solar energy reaches the outer layer of the earth's atmosphere. Nearly half
of it is absorbed while passing through the atmosphere and the rest reaches the
earth's surface.
Solar Constant
The amount of solar
energy received per second by one square metre of the near earth space (exposed
perpendicularly to the rays of the sun) at an average distance between the sun
and the earth is called solar constant.
Solar constant = 1.4
kW/m2
Black Surfaces Absorb
More Heat than White Surfaces
SOLAR COOKER
6. A solar cooker is a heating device
which is used to cook food by utilizing the energy radiated by the sun. A solar
heater is used to heat water by utilizing the energy radiated by the sun. The
solar power plants are used to produce electricity by using the solar energy.
The solar cells are used to convert solar energy directly into electrical
energy. The solar cells are made from semi- conductor elements like silicon and
germanium.
A solar heating device
is one which allows collection of a large amount of heat from the sunlight in a
given region and restricts the loss of heat to the surrounding in the form of
radiation.
The following facts
help us to design an efficient solar cooker:
• A black body absorbs maximum heat
• Loss of heat by convection can be
restricted in a closed system
• Radiation losses can be avoided by
reflecting the rays inside the body with the help of reflecting object like a
plane mirror
• Conduction can be reduced by using
poor conducting materials
• Construction
A solar cooker
contains a wooden box having thermocol lining from inside. A box made aluminium
is placed inside the wooden box. The inner side of the aluminium box is painted
black. The top is closed by a glass sheet. A plane mirror is fixed to the
hinged lid.
The box is closed such
that the inner part does not come in contact with the outside air, there by
reducing heat loss due to convection currents. The glass top reflects the light
in to the box thereby reducing the heat loss due to radiation. The temperature
inside the box is about 100 - 140o C.
A phenomenon similar
to green house effect happens here. The glass top allows infrared radiations
emitted by the sun into the box and traps the infrared radiations emitted by
hot objects inside the cooker.
This type of solar
cooker can be used for cooking. But the time of cooking depends on the
intensity of the sunlight and hence the time taken is shorter in summer and
longer in winter. Rice, pulses and vegetables can be boiled by keeping them
inside the box. Baking and frying can be done in reflector type solar cooker. A
huge spherical concave mirror is used as a reflector.
Another device that
harnesses solar energy is the solar cell. Solar cells are expensive and are
used only when supplying electricity becomes difficult.
Solar cells are the
devices where solar energy is directly converted into electricity.
Sunlight can be used
to run machinery and generate electricity.
About hundred years
ago it was found that when sunlight falls on a thin layer of selenium
electricity is produced. But the efficiency of the conversion was low (as low
as 0.6%). Solar cells were not popular for a long time because of this low
efficiency.
Solar cells are made
of naturally available semiconductors such as silicon and germanium. The
resistivity of these materials is between those of conductors and insulators.
Therefore they are called semiconductors. They behave like insulators at low
temperature and like conductors above room temperature. To increase its
conductivity semiconductors are doped with impurities. Semiconductors which are
doped with impurities like boron or aluminium are termed as p-type
semiconductors and those doped with impurities like phosphorous, are called
n-type semiconductors. In p-type semiconductors holes are majority carriers and
electrons are minority carriers and in n-type semiconductors electrons are
majority carriers and holes are minority carriers.
The first practical
solar cell was constructed in 1954 with an efficiency of 1%. Today we have
selenium based solar cells with an efficiency of 25%.
Construction and
Working of a Solar Cell
Solar cell is a very
thin sandwich of n-type and p-type wafer thin semiconductors of silicon. A
U-shaped metal grid is embedded into the thin semiconductor chip as shown in
the fig. The lower end of the sandwich is fixed to a metal base which has a
metal lead. The grid has a lead contact on the top surface which can be
connected to another solar cell in series. The upper surface of semi conducting
sandwich is coated with anti-reflection coating.
When visible light
falls on the solar cell the n-type wafer produces a large number of electrons.
These electrons drift towards p-type wafer thereby generating an electric
potential.
The potential
difference produced by a single solar cell of 4 cm2 is between 0.4 to 0.5 volts
and the magnitude of electric current is 60 milli-amperes.
However, when a large
number of solar cells are connected in a mixed circuit, i.e., some cells in
series and some in parallel, a large potential difference and large current can
be obtained.
An assembly of solar
cells can be used to generate electricity and such arrangement of cells is
known as solar cell panel.
Question 1:
What kind of mirror −
concave, convex or plain − would be best suited for use in a solar cooker? Why?
• Answer
•
• Discussion
A solar cooker uses
heat of the sunlight to cook and heat food. A mirror is used in order to
reflect and focus sunlight at a point. A concave mirror is used in a solar
cooker for this purpose. The mirror focuses all the incident sunlight at a
point. The temperature at that point increases, thereby cooking and heating the
food placed at that point.
• It is present in abundance
• They have no moving parts and hence
require little maintenance and work quite satisfactorily without any focusing
device
• It does not cause any environmental
pollution like the fossil fuels and nuclear power
• Solar cells last a longer time and
have low running costs
Disadvantages
• The entire process of manufacture is
still very expensive as silver is used for interconnection of these cells in
the panel, which is a very expensive metal.
• Silver is the best conductor of
electricity having very low resistance and it increases its efficiency.
• A practical problem linked with the
use of solar cell panels is regarding the storage of electricity general by
them. The electricity generated by the solar cell panel is stored during the
day with the help of storage batteries which give us only direct current. But
to operate our devices we need alternating current. Therefore we need to
convert DC to AC before using any appliance and thus it increases the cost of
such solar panels as the sources of electricity.
Uses of Solar Cells
Solar cells or solar
cell panels are used in -
• Artificial satellites and in space
probes like Mars orbiters
• Wireless transmission systems or TV
relay stations in remote locations
• Traffic signals, calculators and in
toys
OCEAN –THERMAL ENERGY
About 71% of the earth's
surface is covered by oceans. Energy can be harnessed from
• Tides
• Sea-waves
• Temperature differences in the water
We shall discuss each
energy form in detail:
Tidal Energy
Tides are caused due
the gravitational pull of the moon on the water in oceans and seas. The
enormous movement of water between the high tides and low tides provides a very
large source of energy in the coastal areas of the world. This tidal energy can
be harnessed by constructing a dam or a barrage as shown in the figure given above.
The energy conversion involved in the process is given below:
Working
During high tide, when
the level of water in the sea is high, sea-water flows into the reservoir of
the barrage and turns the turbines. The turbines then turn the generator shaft
to produce electricity.
During low tide, the
sea-water stored in the barrage reservoir is allowed to flow out into the sea.
This flowing water also turns the turbines and generates electricity. Thus, as
the sea-water flows in and out of the tidal barrage during high and low tides,
the turbines rotate continuously to generate electricity.
Limitations
The tides do not
possess enough energy to generate electricity on a large scale
• Only few sites are suitable for
building such barrages (or tidal dams)
Energy from the oceans
is also available in the form of oceanic waves or sea-waves. Due to the blowing
of wind on the surface of ocean, very fast sea-waves (or water waves) move on
its surface. Due to their high speed, sea-waves have a lot of kinetic energy in
them. The energy of moving sea-waves can be used to generate electricity. This
can be done as follows:
• One idea is to set-up floating
generators in the sea such that these would move up and down with the
sea-waves. This movement would drive the generators to provide electricity.
• Another idea is to let the sea-waves
move up and down inside large tubes. As the waves move up, the air in the tubes
is compressed, and this compressed air can then be used to rotate a turbine of
a generator to produce electricity.
These ideas are only
experimental in nature and such models based on these ideas have been made but
it will be many years before full-size wave-energy generators can be built to
harness the sea-waves energy on a large scale.
The water at the surface
of an ocean gets heated by the heat of the sun and attains a higher temperature
than the colder water at deeper levels in the ocean. So, there is always a
temperature difference between the water "at the surface of ocean"
and "at deeper levels." At many places in the ocean, this difference
in temperatures of water is up to 20oC. The energy available due to the
difference in the temperature of water at the surface of the ocean and at
deeper levels is called ocean thermal energy (OTE). The ocean thermal energy
can be converted into "usable form" of energy like electricity. This
can be done as follows:
The devices used to
harness ocean thermal energy are called Ocean Thermal Energy Conversion power
plants (or OTEC power plants). In one type of OTEC power plants, the warm
surface water of ocean is used to boil a liquid like ammonia or a
chlorofluorocarbon (CFC). The high pressure vapours of the liquid (formed by
boiling) are then used to turn the turbine of a generator and produce
electricity. The colder water from the deeper ocean is pumped up to cool the
used up vapours and convert them again into a liquid. This process is repeated
again and again.
Advantages
A greater advantage of
the ocean thermal energy is that it can be used continuously for 24 hours
throughout the year.
• Ocean thermal energy is a renewable
source of energy and its use does not cause any pollution. Sea-wave energy and
ocean thermal energy are the two forms in which solar energy manifests itself
in oceans.
Limitation
The installation and
maintenance of an OTEC power plant is very high and efficient commercial
exploitation is difficult.
6. The oceans act as a storehouse of solar
heat energy. Because the oceans covers almost 71% collector of solar heat
energy. The energy collector of solar heat energy. The energy from the oceans
is available in different forms. They are:
a. Ocean Thermal Energy (OTE)
b. Sea – waves energy
c. Tidal energy
d. Energy from salinity gradient in seas
e. Energy from sea vegetation
f. Energy from the nuclear fusion of deuterium
that is present inoceans
11. There is always some significant
temperature difference between the water ‘at the surface of ocean’ and ‘at
deeper levels’. This temperature difference is even upto 2°C at enable the flow
of heat. The energy available as a result of difference in the temperature
water at the surface of the ocean and at deeper levels is known as ocean
thermal energy. It is also abbreviated as OTE.
12. The rise of ocean water as a result of
moon’s attraction is called ‘high tide and the fall of water is called ‘low
tide’. The rise and fall of tidal waves takes place twice in a day. This gives
rise to enormous movement of water between high tides and low a tides and is an
excellent source of energy in many coastal areas of the world. The tidal energy
can also be harnessed by constructing some tidal barrier or tidal dam.
Question 2:
What are the
limitations of the energy that can be obtained from the oceans?
• Answer
The forms of energy
that can be obtained from the ocean are tidal energy, wave energy, and ocean
thermal energy. There are several limitations in order to harness these
energies.
(i) Tidal energy
depends on the relative positioning of the Earth, moon, and the Sun.
(ii) High dams are
required to be built to convert tidal energy into electricity.
(iii) Very strong
waves are required to obtain electricity from wave energy.
(iv) To harness ocean
thermal energy efficiently, the difference in the temperature of surface water
(hot) and the water at depth (cold) must be 20ºC or more.
'Geo' means earth and
'thermal' means heat. Thus geothermal energy is that heat energy obtained from
hot rocks present inside the earth. This heat can be used as a source of energy
to produce electricity.
You know that the
innermost layer of the earth is called the core. Above the core are the mantle
and the crust. The core is at a temperature of around 4000 oC, and the
temperature decreases as one moves towards the crust. The temperature near the
upper part of the mantle is around 1500 oC. The material here is in a partially
molten state like coal tar. This molten material, mixed with gases, is called
magma. The plates which make up the continents float on the molten magma.
The hot mantle heats
the rocks in the crust above it. Rainwater, which seeps into the ground and
slowly percolates down through cracks in the upper crust, also gets heated by
the hot rock beneath. In certain areas below the earth's surface, hot magma
swells up into the crust, but remains trapped below the surface of the earth.
Such areas in the earth's crust are called hot spots. The rocks and groundwater
above these hot spots get heated and act as reservoirs of geothermal energy.
There are certain regions around the world in which there are a lot of hot
spots relatively close to the earth's surface. Such regions can easily utilize
geothermal energy.
The water trapped in
the rocks, deep below the earth's surface is under tremendous pressure exerted
because of the layers of rocks above it. The boiling point of water increases
with pressure. Thus, the water above a hot spot gets heated to temperatures
above 100 oC (reaching up to 300 oC) without being converted to steam. In some
cases, this superheated water finds its way through the cracks in the rocks and
pushes upwards. On the way up, the pressure on the water decreases gradually.
At lower pressures, the boiling point of water is also lower, and therefore,
the water gets converted into steam. Dry steam or steam mixed with hot water
pushes out of the surface of the earth with great force. The fountain of steam
and water coming out from the surface of the earth is called a geyser. Apart
from this, hot water also comes to the surface and collects in pools called hot
springs. Steam as well as hot water from geothermal sources can be utilized.
Some common uses include heating of buildings and generation of electricity.
Generating Electricity
from Geothermal Energy
Geothermal energy can
be used to generate electricity in various ways. If dry steam comes out of the
surface of the earth, it can be used directly to turn turbines connected to
generators. The world's largest geothermal electric power plant, at Geysers
Steam Field, California, uses this method to generate electricity.
At places where there
is superheated water below the earth's surface but steam remains trapped below
the earth's surface, a different method is used. Two pipes are sunk into the
earth. Through one is pumped cold water which is then converted to steam and
comes out through the other pipe as super heated steam and is used to rotate
the turbines to generate electricity.
Advantages of
Geothermal Energy
Geothermal plants can
operate round the clock, unlike those based on solar and tidal energy
• Geothermal energy is almost
pollution-free
• The cost of a geothermal plant is
high as compared to a coal-based plant, but operating costs are lower
• The source of energy is free and
renewable In India, there are about 400 hot springs that can be tapped for
geothermal energy. Ladakh, Gujarat and Madhya Pradesh have good
geothermal-energy potential. It is estimated that 10,000 MW of electricity can
be generated from geothermal plants in India. However, no plants have yet been
setup.
Disadvantages
Question 3:
What is geothermal
energy?
• Answer
Geothermal power
plants use heat of the Earth to generate electricity. This heat energy of the
Earth is known as geothermal energy.
When there are
geological changes, the molten rocks present in the core of the earth are
pushed to the earth’s crust. This forms regions of hot spot. Steam is generated
when the underground water comes in contact with these hot spots forming hot
springs. This trapped steam is used to generate electricity in the geothermal
power plants
This is another
important source of energy that is obtained from the energy that is stored in
the nucleus of an atom. This stored energy can be obtained by carrying out two
types of nuclear reactions called nuclear fission reaction and nuclear fusion
reaction.
Nuclear Fission
Reaction
The process of
splitting of a heavy nucleus into a number of light nuclei with the liberation
of tremendous amount of energy and two or three neutrons is called nuclear
fission.
• In the fissioning of the Uranium-235
isotope, some mass of Uranium disappears (or is lost) and this small mass gets
converted into tremendous amount of energy governed by Einstein's famous mass-energy
equation
•
Where E = energy
released
m = difference in mass
of the original nucleus and product nuclei
C = velocity of light
[3 x 108 m/s]
This energy is
expressed in terms of electron volt [eV]
1eV = 1.602 x 10 19
Joules
• The fission of an atom of Uranium
produces 10 million times the energy produced by the combustion of an atom of
carbon from coal.
• Nuclear energy is produced in a
nuclear reactor which is a device to generate electricity and used Uranium-235
as its fuel. In this reactor the energy released is controlled or sustained
which is called as sustained fission reaction. Otherwise the energy goes out of
control which becomes an explosive fission reaction. The energy is controlled
by retaining just enough neutrons to undergo fission and the excess neutrons
are absorbed by the control rods in the reactor.
Principle of Nuclear
Power Production
Nuclear fission which
takes place inside the reactor produces tremendous heat. This heat energy is
used to boil water to form super-heated steam, which in turn rotates the
turbines to generate electricity.
Advantages of Nuclear
Power
18. The nuclear reactor (commonly known as
atomic reactor or atomic pile) is a specially designed furnace for carrying out
the controlled fission of a radioactive material line U – 235 for producing
atomic power. The heat energy produced from fission reactions is ultimately
converted into electricity.
19. Nuclear fuel is the fissionable material
used in the nuclear reactor for producing energy by the process of fission. The
nuclear fuel used is enriched which slows down the speed of neutrons so as to
cause the
fission of uranium 235
effectively. Heavy water is an important moderator.
20. The process in which an unstable nucleus
of a heavy atom (like U –
235) splits up into two medium - sized nuclei
with the liberation of an
enormous amount of
energy is called nuclear fission.
92U235 + 0n1 → 56Ba141 + 56Kr92 + 3(0n1) + energy
Question 4:
What are the
advantages of nuclear energy?
• Answer
•
• Discussion
The advantages of
nuclear energy are as follows:
(a) Large amount of
energy is produced per unit mass.
(b) It does not
produce smoke. It is a clean energy.
(c) Fission of one
atom of uranium produces 10 million times the energy released by burning of one
atom of carbon.
(d) Fusion of four
hydrogen atoms produces huge amount of energy approximately equal to 27 MeV.
Question 1:
Can any source of
energy be pollution-free? Why or why not?
• Answer
No source of energy
can be pollution-free. It is considered that solar cells are pollution-free.
However, even their making causes environmental damage indirectly.
Also, in the case of
nuclear energy, there is no waste produced after the fusion reactions. However,
it is not totally pollution-free. To start the fusion reactions, approximately
107 K temperature is required, which is provided by fission reactions. The wastes
released from fission reactions are very hazardous. Hence, no source of energy
is pollution-free.
Question 2:
Hydrogen has been used
as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why
not?
• Answer
Hydrogen gas is cleaner
than CNG. CNG contains hydrocarbons. Therefore, it has carbon contents. Carbon
is a form of pollutant present in CNG. On the other hand, hydrogen is
waste-free. The fusion of hydrogen does not produce any waste. Hence, hydrogen
is cleaner than CNG
Question 1:
Name two energy
sources that you would consider to be renewable. Give reasons for your choices.
• Answer
Two renewable sources
of energy are as follows:
(a) Sun: The energy
derived from the Sun is known as solar energy. Solar energy is produced by the
fusion of hydrogen into helium, fusion of helium into other heavy elements, and
so on. A large amount of hydrogen and helium is present in the Sun. Therefore,
solar energy can replenish on its own. The Sun has 5 billion years more to
burn. Hence, solar energy is a renewable source of energy.
(b) Wind: Wind energy
is derived from air blowing with high speed. Wind energy is harnessed by
windmills in order to generate electricity. Air blows because of uneven heating
of the Earth. Since the heating of the Earth will continue forever, wind energy
will also be available forever.
Question 2:
Give the names of two
energy sources that you would consider to be exhaustible. Give reasons for your
choices.
• Answer
Two exhaustible energy
sources are as follows:
(a) Coal: It is
produced from dead remains of plants and animals that remain buried under the
earth’s crust for millions of years. It takes millions of years to produce
coal. Industrialization has increased the demand of coal. However, coal cannot
replenish within a short period of time. Hence, it is a non-renewable or
exhaustible source of energy.
(b) Wood: It is
obtained from forests. Deforestation at a faster rate has caused a reduction in
the number of forests on the Earth. It takes hundreds of years to grow a
forest. If deforestation is continued at this rate, then there would be no wood
left on the Earth. Hence, wood is an exhaustible source of energy.
Question 1:
• Answer
• •
Question 1:
A solar water heater
cannot be used to get hot water on
(a) a sunny day (b) a
cloudy day
(c) a hot day (d) a
windy day
• Answer
(b) A solar water heater uses solar energy to
heat water. It requires bright and intense sunlight to function properly. On a
cloudy day, the sunlight reflects back in the sky from the clouds and is unable
to reach the ground. Therefore, solar energy is not available for the solar
heater to work properly. Hence, solar water heater does not function on a
cloudy day.
Question 2:
Which of the following
is not an example of a bio-mass energy source?
(a) wood (b) gobar gas
(c) nuclear energy (d) coal
• Answer
(c) Bio-mass is a source of energy that is
obtained from plant materials and animal wastes. Nuclear energy is released
during nuclear fission and fusion. In nuclear fission, uranium atom is
bombarded with low-energy neutrons. Hence, uranium atom splits into two
relatively lighter nuclei. This reaction produces huge amount of energy. In
nuclear fusion reaction, lighter nuclei are fused together to form a relatively
heavier nuclei. This reaction produces tremendous amount of energy. Hence,
nuclear energy is not an example of bio-mass energy source.
Wood is a plant
material, gobar gas is formed from animal dung, and coal is a fossil fuel
obtained from the buried remains of plants and animals. Hence, these are
bio-mass products.
Question 3:
Most of the sources of
energy we use represent stored solar energy. Which of the following is not
ultimately derived from the Sun’s energy?
(a) Geothermal energy
(b) Wind energy
(c) Nuclear energy
(d) Bio-mass
• Answer
•
(c) Nuclear energy is
released during nuclear fission and fusion. In nuclear fission, uranium atom is
bombarded with low-energy neutrons. Hence, uranium atom splits into two
relatively lighter nuclei. This reaction produces huge amount of energy. In
nuclear fusion reaction, lighter nuclei are fused together to form a relatively
heavier nuclei. The energy required to fuse the lighter nuclei is provided by
fission reactions. This reaction produces tremendous amount of energy. These
reactions can be carried out in the absence or presence of sunlight. There is
no effect of sunlight on these reactions. Hence, nuclear energy is not
ultimately derived from Sun’s energy.
Geothermal energy,
wind energy, and bio-mass are all ultimately derived from solar energy.
Geothermal energy is
stored deep inside the earth’s crust in the form of heat energy. The heating is
caused by the absorption of atmospheric and oceanic heat. It is the sunlight
that heats the atmosphere and oceans.
Wind energy is
harnessed from the blowing of winds. The uneven heating of the earth’s surface
by the Sun causes wind.
Bio-mass is derived
from dead plants and animal wastes. Chemical changes occur in these dead plants
and animal wastes in the presence of water and sunlight. Hence, bio-mass is
indirectly related to sunlight.
SOLAR ENERGY
7. The energy radiated by the sun is
called solar energy. It is interesting to note that the solar energy recovered
on the earth in one day is about 50, 000 times more than the total energy
consumed by all the nations of the world in one year.
8. There are two limitations of solar
energy:
a. The solar energy that reaches the earth
is in a very diffused form
b. The solar energy is not uniformly
available at all the time and all the places.
9. Any device that gets heated by the
sun’s energy is called a solar heating device. Such a device helps in
collecting as much solar energy as possible. It is done by using a black
pointed surface, a glass sheet cover and a reflector.
Question 4:
Compare and contrast
fossil fuels and the Sun as direct sources of energy.
• Answer
•
• Discussion
Fossil fuels are
energy sources, such as coal and petroleum, obtained from underneath the
Earth’s crust. They are directly available to human beings for use. Hence,
fossil fuels are the direct source of energy. These are limited in amount.
These are non-renewable sources of energy because these cannot be replenished
in nature. Fossil fuels take millions of years for their formation. If the
present fossil fuel of the Earth gets exhausted, its formation will take
several years. Fossil fuels are also very costly.
On the other hand,
solar energy is a renewable and direct source of energy. The Sun has been
shining for several years and will do so for the next five billion years. Solar
energy is available free of cost to all in unlimited amount. It replenishes in
the Sun itself.
Question 5:
Compare and contrast
bio-mass and hydro electricity as sources of energy.
• Answer
•
• Discussion
Bio-mass and
hydro-electricity both are renewable sources of energy. Bio-mass is derived
from dead plants and animal wastes. Hence, it is naturally replenished. It is
the result of natural processes. Wood, gobar gas, etc. are some of the examples
of bio-mass.
Hydro-electricity, on
the other hand, is obtained from the potential energy stored in water at a
height. Energy from it can be produced again and again. It is harnessed from
water and obtained from mechanical processes.
Question 6:
What are the limitations
of extracting energy from −
(a) the wind? (b)
waves? (c) tides?
• Answer
•
• Discussion
(a) Wind energy is
harnessed by windmills. One of the limitations of extracting energy from wind
is that a windmill requires wind of speed more than 15 km/h to generate
electricity. Also, a large number of windmills are required, which covers a
huge area.
(b) Very strong ocean
waves are required in order to extract energy from waves.
(c) Very high tides
are required in order to extract energy from tides. Also, occurrence of tides
depends on the relative positions of the Sun, moon, and the Earth.
The energy source that
we actually choose depends on various factors like the cost, the ease with
which it is available, the efficiency of the technology available and the
environmental damage that will be caused by using that source.
It is thus debatable
as to whether any source of energy is pollution free or not. Research continues
in these areas to produce longer lasting devices that will cause less damage
throughout their life.
Thus the energy source
that we should be:
• of low
• energy efficient and
• pollution free
• easily available to us
We may broadly
classify energy sources as renewable and non- renewable sources of energy.
Renewable source of energy is the source which is available in our natural
environment and can be used repetitively. Sun, wind and water are renewable
sources of energy.
Non-renewable source
of energy is the energy source that will get depleted some day. They are also
called exhaustible sources. coal and petroleum are non - renewable sources of
energy.
Conclusion
Exploiting any energy
source disturbs the environmental balance and must be harnessed judicially.
Question 7:
On what basis would
you classify energy sources as
(a) renewable and non-renewable?
(b) exhaustible and
inexhaustible?
Are the options given
in (a) and (b) the same?
• Answer
•
• Discussion
(a) The source of
energy that replenishes in nature is known as renewable source of energy. Sun,
wind, moving water, bio-mass, etc. are some of the examples of renewable
sources of energy.
The source of energy
that does not replenish in nature is known as non-renewable source of energy.
Coal, petroleum, natural gas, etc. are some of the examples of non-renewable
sources of energy.
(b) Exhaustible
sources are those sources of energy, which will deplete and exhaust after a few
hundred years. Coal, petroleum, etc. are the exhaustible sources of energy.
Inexhaustible
resources of energy are those sources, which will not exhaust in future. These
are unlimited. Bio-mass is one of the inexhaustible sources of energy.
Yes. The options given
in (a) and (b) are the same.
Question 9:
What are the
advantages and disadvantages of using a solar cooker? Are there places where
solar cookers would have limited utility?
• Answer
•
• Discussion
Solar cooker uses
Sun’s energy to heat and cook food. It is inexhaustible and clean renewable
source of energy. It is free for all and available in unlimited amount. Hence,
operating a solar cooker is not expensive.
Disadvantage of a
solar cooker is that it is very expensive. It does not work without sunlight.
Hence, on cloudy day, it becomes useless.
The places where the
days are too short or places with cloud covers round the year, have limited
utility for solar cooker
Question 10:
What are the
environmental consequences of the increasing demand for energy? What steps
would you suggest to reduce energy consumption?
• Answer
Industrialization
increases the demand for energy. Fossil fuels are easily accessible sources of
energy that fulfil this demand. The increased use of fossil fuels has a harsh
effect on the environment. Too much exploitation of fossil fuels increases the
level of green house gas content in the atmosphere, resulting in global warming
and a rise in the sea level.
It is not possible to
completely reduce the consumption of fossil fuels. However, some measures can
be taken such as using electrical appliances wisely and not wasting
electricity. Unnecessary usage of water should be avoided. Public transport
system with mass transit must be adopted on a large scale. These small steps
may help in reducing the consumption of natural resources and conserving them.
Energy can be defined
as the ability to do work.
A good source of
energy would be the one which would:
• do a large amount of work per unit
volume or mass
• be easily accessible
• be easy to store and transport and
• be economical
Fossil Fuel
Fossil fuel is a
hydrocarbon deposit, such as petroleum, coal, or natural gas, derived from
living matter of a previous geologic time and used for fuel.
Power Station
A power station or a
power plant is a facility for the generation of electric power.
Thermal Power Plant
• A thermal power plant utilizes
thermal energy of fuels such as coal, oil, natural gas or radioactive
substances for the generation of electric power.
• In a thermal power plant the chemical
energy stored in fossil fuels or radioactive substances is converted
successively into thermal energy, mechanical energy and, finally to electrical
energy.
Hydro Power Plant
• In a hydro power plant electricity is
produced from water.
• Hydro power plants convert the
potential energy of falling water into electricity.
Wind Energy
• Moving air is called wind
• Wind possesses kinetic energy
• Wind energy can be used to sail
boats, grind grains, pump water and generate electricity
Solar Energy
• Solar energy is used for:
- heating water for
domestic use
- space heating of buildings
- heating swimming
pools
- drying agricultural
products and for generating electrical energy
• Biomass is an organic material
obtained from plants and animals
•
Solar Cell
• A typical solar cell develops a
voltage of 0.5-1 Volt and can produce about 0.7 Watt of electricity when
exposed to the Sun
• A solar cell panel is an assembly of
solar cells used to generate electricity.
• Solar cells or solar cell panels are
used in:
- Artificial
satellites and in space probes like Mars orbiters
- Wireless transmission
systems or TV relay stations in remote locations
- Traffic signals,
calculators and in toys
Tidal Energy
Tidal Energy,
sometimes called tidal power, is the power achieved by capturing the energy
contained in moving water in tides and ocean currents.When tides come into the
shore, they are trapped in reservoirs behind dams. Then when the tide drops,
the water behind the dam is let out just like in a regular hydroelectric power
plant.
Wave Energy
The huge moving waves
possess kinetic energy. This energy is used to power a turbine. Most
wave-energy systems are very small. But, they can be used to power a warning
buoy or a small light house.
Ocean Thermal Energy
The energy obtained by
converting the solar energy trapped by the ocean into useable energy is known
as ocean thermal energy.
The ocean energy
plants can operate only if the temperature difference between the water at the
surface and water at depths up to 2 km is 293 K or 20 0C or more.
Geothermal Energy
Energy obtained by
tapping underground reservoirs of heat, usually near volcanoes or other hot
spots on the surface of the Earth is known as geothermal energy.
Nuclear Reactions
Nuclear reactions are
those reactions where in a nucleus when bombarded with nucleons or other
sub-atomic particles; undergoes a change in its composition.
Nuclear Fission
Reaction
The process of
splitting of a heavy nucleus into a number of light nuclei with the liberation
of tremendous amount of energy and two or three neutrons is called nuclear
fission.
Nuclear Fusion
Reaction
Nuclear fusion is a
reaction in which two or more light nuclei combine to form a heavier nucleus
releasing an enormous amount of energy:
• Nuclear fusion takes place at a very
high temperature of the order of 107 Kelvin
• Hence nuclear fusion reaction is
called thermo nuclear reaction
• Nuclear fusion is the type of
reaction taking place inside the sun
• Inside the core of the sun fast
moving hydrogen nuclei combine to form helium nucleus. Nuclear fusion is the
basic principle of the Hydrogen bomb.
Nuclear Reactor
A nuclear reactor is a
device or a furnace where controlled fission chain reaction is carried out and
the energy released is used to generate electricity.
Question 1
Question: Name the following:
1) Two renewable
sources of energy (non - conventional)
2) Two non-renewable
or conventional sources of energy
3) Two forms of energy
usually used at homes
4) The radiation
emitted from a hot source
5) The component of
sunlight that is absorbed by the ozone layer of the atmosphere.
6) Two activities in
our daily life in which solar energy is used
7) The kind of surface
that absorbs maximum heat
8) The device that
directly converts solar energy into electrical energy
9) The range of
temperature attained inside a box-type solar cooker placed in the sun for 2-3
hours
10) The two elements
which are used to fabricate solar cells
Answer:
1) Sun and wind
2) Coal and Wood
3) Heat energy and
Electrical energy
4) Infra-red rays
5) Ultra-violet rays
6) Cooking food using
solar cookers and drying clothes and food grains
7) Black Surface
8) Solar cell
9) 100 oC - 140 oC
10) Silicon and
Germanium
Question 2
Question: State an important characteristic of a
source of energy.
Answer: It should supply enough amount of useful
energy in a controlled manner.
Question 3
Question: Which component of sun's energy is
responsible for drying clothes?
Answer: Infra-red rays
Question 4
Question: Define solar constant.
Answer: The amount of solar energy received per
second by 1m2 area of the earth's surface at an average distance between the
sun and the earth. It's value is 1.4 kW/m2.
Question 5
Question: What type of energy is possessed by wind?
Answer: Kinetic energy
Question 6
Question: Though a hot iron emits radiations, it is
not visible to us. Why?
Answer: It emits infra-red radiations which are
invisible to the eyes.
Question 7
Question: What type of radiations is emitted by a 100
W electric bulb?
Answer: Visible light and infra-red radiations are
the two types of radiations emitted by a 100 W electric bulb.
Question 8
Question: How is the conductivity of a semi-conductor
affected when light falls on it?
Answer: The conductivity of the semi-conductor
increases.
Question 9
Question: What is the main cause for winds to blow?
Answer: Due to unequal heating of the earth's
surface there is a difference in pressure in the atmosphere. The air moves from
region of high pressure (cold region) to the region of low pressure (hot
region). This moving air is called wind.
Question 10
Question: What is the minimum wind speed required for
generating electricity in a wind mill?
Answer: The wind velocity must be at least 15km/hr.
Question 11
Question: What is a wind farm?
Answer: The region where large number of windmills
is erected to produce electricity is called a wind farm.
Question 12
Question: Name the constituent elements present in
coal.
Answer: Carbon, Hydrogen, Oxygen and small amount
of sulphur and nitrogen are present in coal.
Question 13
Question: Where are the thermal power plants generally
setup?
Answer: Near coal or oil fields so that the fuel
can be easily transported.
Question 14
Question: What is the principle involved in the
working of the thermal power plant?
Answer: In a thermal power station, coal is burnt
in a boiler and the water in the boiler is converted to steam. Steam under
high-pressure is directed onto a turbine, to turn the turbine shaft. This shaft
which is connected to an electrical generator produces electricity as it turns.
A condenser converts the spent steam from the turbine back to water and this
water is pumped back into the boiler.
Question 15
Question: What is the energy conversion involved in a
thermal power plant?
Answer: In a thermal power plant the chemical
energy stored in fossil fuels or radioactive substances is converted
successively into thermal energy, mechanical energy and, finally to electrical
energy.
Question 16
Question: What kind of energy does the flowing water
possess?
Answer: Kinetic energy
Question 17
Question: How does construction of dams on rivers help
mankind?
Answer: It helps in controlling floods and also
helps in irrigation.
Question 18
Question: Why is biomass considered as a steady source
of energy?
Answer: Biomass is considered as a steady source of
energy due to the large livestock population of our country.
Question 19
Question: What is Biomass?
Answer: Biomass is an organic material obtained
from plants and animals. Some examples of biomass fuels are wood, crops,
manure, and some garbage.
Question 20
Question: What is biogas?
Answer: Biogas is a mixture of various gases formed
when the animal dung mixed with water is allowed to decompose by anaerobic
micro organisms.
Question 21
Question: Which gases constitute the biogas?
Answer: Methane, carbon-di-oxide, hydrogen and
hydrogen sulphide are the main constituents of the biogas.
Question 22
Question: What are the uses of biogas?
Answer: Used in gas stove as fuel in rural areas,
street lighting and also for running engines.
Question 23
Question: What are the raw materials required for a
biogas plant?
Answer: Animal dung, poultry wastes, plant wastes,
human excreta, industrial wastes and domestic wastes.
Question 24
Question: What is the principle of the biogas plant?
Answer: Biogas is produced as a result of anaerobic
fermentation of biomass in the presence of water.
Question 25
Question: What is combustion?
Answer: The chemical process in which a substance
burns in air or oxygen with the release of heat and light energy is called
combustion.
Question 26
Question: What is anaerobic degradation?
Answer: Decomposition taking place in the absence
of oxygen by anaerobic bacteria is known as anaerobic degradation.
Question 27
Question: Define ignition temperature.
Answer: The minimum temperature at which a
substance catches fire and starts burning.
Question 28
Question: Why is the slurry from a bio-gas plant used
as manure?
Answer: It is rich in nitrogen and phosphorous and
is thus excellent manure.
Question 29
Question: Write the principle of the windmill?
Answer: The blowing wind strikes across the blades
of the windmill which is placed at an angle. The wind exerts a force on these
blades and rotates it. This in turn rotates the turbine to generate
electricity.
Question 30
Question: Why is wind energy maps prepared?
Answer: It gives us an idea of the average wind
velocity throughout the year at different places.
Question 31
Question: Where is the largest wind energy farm
established in India?
Answer: The largest wind energy farm in India is
located at Kanyakumari in Tamil Nadu.
Question 32
Question: What are the different forms of energy
obtained from ocean?
Answer: Tidal energy, Wave energy and Ocean thermal
energy.
Question 33
Question: What is the energy conversions involved in
the tidal powered electric plant?
Answer:
Question 41
Question: What is a nuclear reactor?
Answer: A nuclear reactor is a device or a furnace
where controlled fission chain reaction is carried out and the energy released
is used to generate electricity.
Question 42
Question: Define nuclear fusion reaction.
Answer: Nuclear fusion is a reaction in which two
or more light nuclei combine to form a heavier nucleus releasing an enormous
amount of energy.
Question 43
Question: Why is fusion reaction preferred to fission
reaction?
Answer: The fusion reaction releases energy which
is ten times more than fission process. Moreover there are no radioactive
by-products that need to be disposed.
Question 44
Question: Give two main differences between renewable
and non-renewable sources of energy.
Answer:
Renewable Source of
Energy Non -renewable Source of Energy
Can be used again and
again Cannot be used again and again
Not exhaustible
(non-conventional energy) Is
exhaustive (conventional energy)
Examples: Solar
energy, Wind energy Examples: Coal and
petroleum
Renewable Source of
EnergyNon -renewable Source of EnergyCan be used again and againCannot be used
again and againNot exhaustible (non-conventional energy)Is exhaustive
(conventional energy)Examples: Solar energy, Wind energyExamples: Coal and
petroleum
Question 45
Question: A sheet of glass is used in solar heating
devices. Why?
Answer: Glass sheet has a property that allows the
infra-red rays of short wavelength from the sun to get into the device but does
not allow the infra-red rays of longer wavelength to leave the solar heating
device. Thus the energy is trapped inside the heating device. Glass sheet
produces green-house effect.
Question 46
Question: Why is a reflector used in a solar cooler?
Answer: The plane mirror is used as reflector. It
is used to concentrate solar energy inside the device and thereby increase its efficiency.
Question 47
Question: Why is the inner side of the solar cooker
painted black?
Answer: Black colour is a very good absorber of
heat and a very poor reflector. So it maximises the absorption of heat and also
retains heat.
Question 48
Question:
1) The use of wood as
a fuel is not advised although forests can be replenished. Explain why?
2) The use of dry wood
as domestic fuel is not considered as good. State any two reasons for it.
Answer: 1) Deforestation (i.e., cutting of tress in
large number) causes many problems like floods, erosion of fertile land and
environmental imbalance.
2) Replenishment of
forests takes long time and as such wood cannot be available to supply
continuous energy.
Question 49
Question: Why the sun is called the ultimate source of
fossil fuels?
Answer: Fossil fuels are formed by the deposition
of plants and animals in the course of millions of years. These plants and
animals during their lifetime directly or indirectly were depended on the sun
for their survival.
Question 50
Question: How were fossil fuels formed?
Answer: The dead plants and animals which were
buried deep under the earth for millions of years got converted into fossil
fuels like coal, petroleum and natural gas. This happens because of absence of
oxygen, high pressure, heat and bacterial action.
Question 51
Question: Mention two disadvantages of using wood as
fuel.
Answer: 1) While burning wood, major portion of the
heat is lost to the surroundings and only 8% of the total heat is actually used
for cooking so it is wasted.
2) Lot of smoke is
produced due to incomplete combustion leading to air pollution and health
hazards.
Question 52
Question: State two limitations of solar energy.
Answer: 1) The solar energy reaches the earth's surface
in a diffused form. It has been estimated that the solar energy received in the
upper atmosphere is 1.4 kW/m2. Thus, it is too small for doing useful work.
2) It is not available
uniformly all the time and at all the places of the earth. It is more in the
Equatorial Regions than in the Polar Regions.
Question 53
Question: State two limitations of biogas plants.
Answer: 1) The initial cost of installation is very
high.
2) The number of
cattle owned by an average family of farmers is inadequate to feed a biogas
plant.
Question 54
Question: What are the two advantages of wind energy?
Answer: 1) Wind energy is a natural resource and is
available with out any cost
2) It does not cause
any kind of pollution
Question 55
Question: Explain the principle underlying the working
of a solar cell.
Answer: Solar cell is a device which directly
converts solar energy into electrical energy. This principle is based on the
phenomenon of photovoltaic effect. The Phenomenon due to which light energy
directly changes into electrical energy, when light is incident on certain
sensitive materials (semi conductors) is called photovoltaic effect.
Question 56
Question: What is a solar panel?
Answer: A group of solar cells connected in
specific pattern to produce desired potential difference and magnitude of
current is called a solar panel. The energy stored in the solar panel with the
help of storage batteries gives us only direct current.
Question 57
Question: State the two limitations of tidal energy.
Answer: 1) The tides do not possess enough energy
to generate electricity on a large scale.
2) Only few sites are
suitable for building such barrages.
Question 58
Question: How are hotspots created in the earth's
crust?
Answer: The upper part of the mantle is very hot
(1500 oC) and as a result the rocks in contact with gets heated up. Rain water
which seeps into the ground slowly percolates through the cracks in the upper
crust and they also get heated. This water gets collected at certain places close
to the earth's surface and are called hotspots.
Question 59
Question: What are natural geysers?
Answer: In some places, the steam formed under the
surface of the earth does not get trapped. Instead it forces its way up through
the cracks in the rocks along with hot water and gushes out from the surface of
the earth to form natural geysers.
Question 60
Question: What are the two kinds of nuclear reactions?
Define them.
Answer: Nuclear Reactions are broadly classified as
nuclear fission reaction and nuclear fusion reaction. Nuclear Fission Reaction
The process of splitting of a heavy nucleus into a number of light nuclei with
the liberation of tremendous amount of energy and two or three neutrons is
called nuclear fission. Nuclear Fusion Reaction Nuclear fusion is a reaction in
which two or more light nuclei combine to form a heavier nucleus releasing an
enormous amount of energy. Nuclear fusion takes place at a very high
temperature of the order of 107 Kelvin.
Question 61
Question: Write two differences between nuclear
fission and fusion reactions.
Answer:
Nuclear Fission Nuclear Fusion
A heavy nucleus splits
up into two or more light nuclei Two
light nuclei combine together to form a heavy nucleus
Harmful nuclear
radiations are emitted and this causes pollution No harmful radiations are emitted and hence pollution free
Nuclear FissionNuclear
FusionA heavy nucleus splits up into two or more light nucleiTwo light nuclei
combine together to form a heavy nucleusHarmful nuclear radiations are emitted
and this causes pollutionNo harmful radiations are emitted and hence pollution
free
Question 62
Question: What principle governs the nuclear
reactions?
Answer: When a heavy nucleus of elements like
Uranium or Plutonium is split or when the lighter elements such as hydrogen or
deuterium is used to form a heavy element, the total mass of products is less
than that of participating atoms. This difference in mass is converted into
energy. This energy released is given by Einstein's famous equation E=mc2 where
'E' stands for energy released, 'm' stands for difference in mass of the
original and the product nucle and 'c' stands for velocity of light which is
equal to 3 x 108 m/s.
Question 63
Question: Why is biogas a better fuel than animal dung
cakes?
Answer: Biogas is a better fuel than animal dung
cakes, because:
1) Burning of animal
dung - cake causes lot of pollution whereas biogas is smokeless fuel.
2) The calorific value
of animal dung-cake is much lower than that of biogas.
3) Animal dung cakes
leave residue after burning whereas biogas leaves no residue.
Question 64
Question: State the characteristics of a good fuel.
Answer: A good source of fuel would be the one
which would:
1) do a large amount
of work per unit volume or mass
2) be easily
accessible
3) be easy to store
and transport and
4) be economical
Question 65
Question: State the advantage of hydel energy?
Answer: 1) The water required for generating hydel
power is available free of cost
2) Hydel power
stations are pollution free
3) The construction of
dams on the rivers helps in the flood control and provides water for irrigation
Question 66
Question: State the limitation of hydel energy.
Answer:
1. A vast variety of flora and fauna as
well as human settlements get submerged in the water of the reservoir. Thus,
animals and people are rendered homeless.
2. It disturbs the ecological balance in
the downstream area of the river. As there are no annual floods due to
construction of the dam. This downstream region does not get nutrient rich silt
and decreases the fertility of the soil and finally the crop yields also
decrease.
3. The fish in the downstream area do not
get sufficient nutrient materials and they die.
4. The vegetation which is submerged rots
under anaerobic conditions and gives rise to large amounts of methane which is
a green- house gas.
5. It creates the problem of satisfactory
rehabilitation of displaced people
Question 67
Question: Mention the conditions necessary for the
formation of biogas.
Answer: 1) A fairly large amount of water should be
added to the animal dung to make the slurry.
2) This slurry should
be made to ferment only in the absence of air (anaerobic fermentation)
3) The temperature of
the slurry should be maintained around 35 oC
Question 68
Question: Mention the advantages of fixed dome type
biogas plant.
Answer: 1) It requires raw materials which are
easily available like animals and plant waste, human excreta, waste food
materials etc.
2) It is inexpensive
3) The construction of
the plant is easy as it is constructed by cement and bricks
Question 69
Question: Explain the working of a windmill.
Answer: Wind turbines are used to produce
electricity. The windmills that generate electricity are conventional in their
propeller design, which employs 2 or 3 tapered blades.
The axle of the
windmill is connected to the shaft of an armature in the generator. When the
fast moving wind rotates the blades of the windmill, the armature inside the
generator rotates and produces electricity.
Question 70
Question: Describe a simple activity to show that a
black surface absorbs more heat than a white one. What is your observation and
inference?
Answer: 1) Take two conical flasks and paint one
white and the other black
2) Fill them with
equal amount of water and place them in sunlight for one hour
3) Touch the flasks
and find out which one is hotter
4) You may also use a
laboratory thermometer to record the exact temperature
Observation and
Inference The thermometer in the black conical flask records a higher
temperature. This is because black surface absorbs more heat than any other
surface under identical conditions. The above concept is used in designing the
device called the solar cooker.
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Question 1:
What
are the disadvantages of fossil fuels?
·
The
disadvantages of fossil fuels are as follows:
(a)
Burning of coal and petroleum produces a lot of pollutants causing air
pollution.
(b)
Fossil fuels release oxides of carbon, nitrogen, sulphur, etc. that cause
acid rain, which affects the soil fertility and potable water.
(c)
Burning of fossil fuels produce gases such as carbon dioxide that causes
global warming.
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Question 2:
Why
are we looking at alternate sources of energy?
Fossil
fuels, which have been traditionally used by human beings as an energy
sources, are non-renewable sources of energy. These sources of energy are
limited and cannot replenish on their own. They are being consumed at a large
rate. If this rate of consumption continues, then the fossil fuels would be
exhausted from the Earth. Therefore, we have to conserve the energy sources.
Hence, we should look for alternate sources of energy.
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Question 3:
How
has the traditional use of wind and water energy been modified for our
convenience?
·
Answer
Traditionally, waterfalls were used as a source of potential energy which was
converted to electricity with the help of turbines. Since waterfalls are few
in number, water dams have been constructed in large numbers. Nowadays,
hydro-dams are used in order to harness potential energy of stored water. In
water dams, water falls from a height on the turbine, which produces
electricity.
Earlier,
the windmills were used to harness wind energy to do mechanical work such as
lifting/drawing water from a well. Today, windmills are used to generate
electricity. In windmills, the kinetic energy of wind is harnessed and
converted into electricity. The rotatory motion of the blades turns the
turbine of the electric generator to generate electricity.
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Question 3:
What
is geothermal energy?
Geothermal
power plants use heat of the Earth to generate electricity. This heat energy
of the Earth is known as geothermal energy.
When
there are geological changes, the molten rocks present in the core of the
earth are pushed to the earth’s crust. This forms regions of hot spot. Steam
is generated when the underground water comes in contact with these hot spots
forming hot springs. This trapped steam is used to generate electricity in
the geothermal power plants
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Question 4:
What
are the advantages of nuclear energy?
·
The
advantages of nuclear energy are as follows:
(a)
Large amount of energy is produced per unit mass.
(b)
It does not produce smoke. It is a clean energy.
(c)
Fission of one atom of uranium produces 10 million times the energy released
by burning of one atom of carbon.
(d)
Fusion of four hydrogen atoms produces huge amount of energy approximately
equal to 27 MeV.
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Question 2:
Hydrogen
has been used as a rocket fuel. Would you consider it a cleaner fuel than
CNG? Why or why not?
Hydrogen
gas is cleaner than CNG. CNG contains hydrocarbons. Therefore, it has carbon
contents. Carbon is a form of pollutant present in CNG. On the other hand,
hydrogen is waste-free. The fusion of hydrogen does not produce any waste.
Hence, hydrogen is cleaner than CNG
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Question 2:
Give
the names of two energy sources that you would consider to be exhaustible.
Give reasons for your choices.
Two
exhaustible energy sources are as follows:
(a)
Coal: It is produced from dead remains of plants and animals that remain
buried under the earth’s crust for millions of years. It takes millions of
years to produce coal. Industrialization has increased the demand of coal.
However, coal cannot replenish within a short period of time. Hence, it is a
non-renewable or exhaustible source of energy.
(b)
Wood: It is obtained from forests. Deforestation at a faster rate has caused
a reduction in the number of forests on the Earth. It takes hundreds of years
to grow a forest. If deforestation is continued at this rate, then there
would be no wood left on the Earth. Hence, wood is an exhaustible source of
energy.
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Question 1:
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Question 4:
Compare
and contrast fossil fuels and the Sun as direct sources of energy.
·
Fossil
fuels are energy sources, such as coal and petroleum, obtained from
underneath the Earth’s crust. They are directly available to human beings for
use. Hence, fossil fuels are the direct source of energy. These are limited
in amount. These are non-renewable sources of energy because these cannot be
replenished in nature. Fossil fuels take millions of years for their
formation. If the present fossil fuel of the Earth gets exhausted, its
formation will take several years. Fossil fuels are also very costly.
On
the other hand, solar energy is a renewable and direct source of energy. The
Sun has been shining for several years and will do so for the next five
billion years. Solar energy is available free of cost to all in unlimited
amount. It replenishes in the Sun itself.
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Question 5:
Compare
and contrast bio-mass and hydro electricity as sources of energy.
·
Bio-mass
and hydro-electricity both are renewable sources of energy. Bio-mass is
derived from dead plants and animal wastes. Hence, it is naturally
replenished. It is the result of natural processes. Wood, gobar gas,
etc. are some of the examples of bio-mass.
Hydro-electricity,
on the other hand, is obtained from the potential energy stored in water at a
height. Energy from it can be produced again and again. It is harnessed from
water and obtained from mechanical processes.
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Question 10:
What
are the environmental consequences of the increasing demand for energy? What
steps would you suggest to reduce energy consumption?
Industrialization
increases the demand for energy. Fossil fuels are easily accessible sources
of energy that fulfil this demand. The increased use of fossil fuels has a
harsh effect on the environment. Too much exploitation of fossil fuels
increases the level of green house gas content in the atmosphere, resulting
in global warming and a rise in the sea level.
It
is not possible to completely reduce the consumption of fossil fuels.
However, some measures can be taken such as using electrical appliances
wisely and not wasting electricity. Unnecessary usage of water should be
avoided. Public transport system with mass transit must be adopted on a large
scale. These small steps may help in reducing the consumption of natural
resources and conserving them.
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BIOGAS
Biogas
is a clean and efficient fuel. It is a mixture of methane (CH4), carbon dioxide
(CO2), hydrogen (H2) and hydrogen sulphide (H2S).
The
chief constituent of biogas is methane (upto 75%).
Production
of Biogas - Fixed Dome Type Biogas Plant
Raw
Materials Required
Forms
of biomass listed below may be used along with water:
• Animal dung
• Poultry wastes
• Plant wastes ( Husk, grass, weeds
etc.)
• Human excreta
• Industrial wastes(Saw dust,
wastes from food processing industries)
• Domestic wastes (Vegetable peels,
waste food materials)
Principle:-Biogas
is produced as a result of anaerobic fermentation of biomass in the presence of
water.
Construction
The
biogas plant is a brick and cement structure having the following five
sections:
• Mixing tank present above the
ground level
• Inlet chamber: The mixing tank
opens underground into a sloping inlet chamber
• Digester: The inlet chamber opens
from below into the digester which is a huge tank with a dome like ceiling. The
ceiling of the digester has an outlet with a valve for the supply of biogas
• Outlet chamber: The digester
opens from below into an outlet chamber
• Overflow tank: The outlet chamber
opens from the top into a small over flow tank
•
Working
• The various forms of biomass are
mixed with an equal quantity of water in the mixing tank. This forms the slurry
• The slurry is fed into the
digester through the inlet chamber. The temperature of the slurry must be
maintained around 35 oC. Any drop in temperature will reduce the anaerobic
activity and hence the yield of biogas
• When the digester is partially
filled with the slurry, the introduction of slurry is stopped and the plant is
left unused for about two months
• During these two months,
anaerobic bacteria present in the slurry decompose or ferment the biomass in
the presence of water
• As a result of anaerobic
fermentation, biogas is formed, which starts collecting in the dome of the
digester
• As more and more biogas starts
collecting, the pressure exerted by the biogas forces the spent slurry into the
outlet chamber
• From the outlet chamber, the
spent slurry overflows into the overflow tank
• The spent slurry is manually
removed from the overflow tank and used as manure for plants
• The gas valve connected to a
system of pipelines is opened when a supply of biogas is required
• To obtain a continuous supply of
biogas, a functioning plant can be fed continuously with the prepared slurry
•
Advantages of Fixed
Dome Type of Biogas Plant
• Requires only locally and easily
available materials for construction
• Inexpensive
• Easy to construct
• Due to the above reasons, this
plant is also called the Janata Gobar gas plant.
Advantages of Biogas as
a Fuel
• As domestic fuel
• For street lighting
• For generation of electricity
• High calorific value
• Clean and excellent fuel
containing upto 75% methane
• No residue produced
• No smoke produced
• Non - polluting
• The slurry is periodically
removed and used as excellent manure which is rich in nitrogen and phosphorous
• Economical
• Can be supplied through pipe
lines
• Burns readily - has a convenient
ignition temperature
Advantages
of Biogas Plants
o Reduces burden on forests and
fossil fuels
o Produces a clean fuel - helps in
controlling air pollution
o Provides nutrient rich (N & P)
manure for plants
o Controls water pollution by
decomposing sewage, animal dung and human excreta
Limitations
of Biogas Plants
o Initial cost of installation of
the plant being high, and is beyond the reach of an average rural Indian
o Number of cattle owned by an
average family of farmers is inadequate to feed a biogas plant
Question
2
Question: State an important characteristic of a
source of energy.
Answer: It should supply enough amount of useful
energy in a controlled manner.
Question
3
Question: Which component of sun's energy is
responsible for drying clothes?
Answer: Infra-red rays
Question
4
Question: Define solar constant.
Answer: The amount of solar energy received per
second by 1m2 area of the earth's surface at an average distance between the
sun and the earth. It's value is 1.4 kW/m2.
Question
5
Question: What type of energy is possessed by wind?
Answer: Kinetic energy
Question
6
Question: Though a hot iron emits radiations, it is
not visible to us. Why?
Answer: It emits infra-red radiations which are
invisible to the eyes.
Question
7
Question: What type of radiations is emitted by a 100
W electric bulb?
Answer: Visible light and infra-red radiations are
the two types of radiations emitted by a 100 W electric bulb.
Question
8
Question: How is the conductivity of a semi-conductor
affected when light falls on it?
Answer: The conductivity of the semi-conductor
increases.
Question
9
Question: What is the main cause for winds to blow?
Answer: Due to unequal heating of the earth's
surface there is a difference in pressure in the atmosphere. The air moves from
region of high pressure (cold region) to the region of low pressure (hot
region). This moving air is called wind.
Question
10
Question: What is the minimum wind speed required for
generating electricity in a wind mill?
Answer: The wind velocity must be at least 15km/hr.
Question
11
Question: What is a wind farm?
Answer: The region where large number of windmills
is erected to produce electricity is called a wind farm.
Question
12
Question: Name the constituent elements present in
coal.
Answer: Carbon, Hydrogen, Oxygen and small amount
of sulphur and nitrogen are present in coal.
Question
13
Question: Where are the thermal power plants generally
setup?
Answer: Near coal or oil fields so that the fuel
can be easily transported.
Question
14
Question: What is the principle involved in the
working of the thermal power plant?
Answer: In a thermal power station, coal is burnt
in a boiler and the water in the boiler is converted to steam. Steam under
high-pressure is directed onto a turbine, to turn the turbine shaft. This shaft
which is connected to an electrical generator produces electricity as it turns.
A condenser converts the spent steam from the turbine back to water and this
water is pumped back into the boiler.
Question
15
Question: What is the energy conversion involved in a
thermal power plant?
Answer: In a thermal power plant the chemical
energy stored in fossil fuels or radioactive substances is converted
successively into thermal energy, mechanical energy and, finally to electrical
energy.
Question
23
Question: What are the raw materials required for a
biogas plant?
Answer: Animal dung, poultry wastes, plant wastes,
human excreta, industrial wastes and domestic wastes.
Question
24
Question: What is the principle of the biogas plant?
Answer: Biogas is produced as a result of anaerobic
fermentation of biomass in the presence of water.
Question
25
Question: What is combustion?
Answer: The chemical process in which a substance
burns in air or oxygen with the release of heat and light energy is called
combustion.
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