Sources of energy class 10 Science notes | Sources of energy class 10 questions and answers

This chapter is very important from examination point of view. A lot of questions are being asked in almost all the 10th class board exams from this chapter. This chapter is also important from the point of view of other competitive exams conducted by JKSSB, JKPSC, UPSC and other boards and commissions for various posts.

Notes For Sources Of Energy Class 10 Science

In the forthcoming section, you will get Sources of energy class 10 notes. You will get to read the concepts like energy, conventional and non conventional sources, advantages and disadvantages of various sources of energy etc. These notes are in the form of questions and answers, so that you can get the maximum benefits. These notes have been prepared by a team of experts who have an experience of more than 10 years of teaching science at secondary level.

What is energy?

By energy we mean the ability or capacity to do work. We use energy to do work. If there is no energy, all our activities will come to a hault. So energy is essential for our survival in this world.

What is a source of energy? What are the characteristics of a good source of energy?

A source of energy is one which can provide adequate amount of energy in a convenient form over a long period of time.

The important characteristics of a good source of energy are:

it should be safe and convenient to use.
It should be cheap and easily available.
It should be easy to store and transport.
It should not cause environmental pollution.

How are energy sources classified? | Classification of energy sources.

The sources of energy are classified either as: (1) renewable and non-renewable sources of energy or (2) Conventional and non conventional sources of energy.

Renewable and non renewable sources of energy:

Renewable sources of energy: The energy sources which are being produced continuously in nature and are inexhaustible. e.g. solar energy, wind energy, water energy, biomass energy etc.

Advantages of renewable sources of energy are:

These sources will last so long as the earth receives light from the sun.
These sources are freely available in nature.
These sources do not cause any pollution.

Since these sources of energy will never get exhausted, so they are also called as inexhaustible sources of energy.

Non-renewable sources of energy: Those sources of energy which are exhaustible and can not be replaced quickly once they have been used. These sources have been accumulated in nature over a very long period of millions of years, e.g. coal, petroleum, natural gas.

Disadvantages of non-renewable sources of energy:

Owing to their fast rate of usage, and non replenishing nature these sources are fast depleting.
It is difficult to discover and exploit new deposits of these sources.
These sources are a major cause of environmental pollution.

Conventional and non conventional sources of energy:

Conventional sources of energy: The sources of energy which are used extensively and meet a major portion of our requirement. e.g. fossil fuels, hydro energy. biomass energy and wind energy.

Non-conventional sources of energy: The energy sources which are not used as extensively as conventional ones and meet our requirement only at a limited scale. e.g. solar energy, ocean energy, geothermal energy and nuclear energy. These sources of energy are being utilized more and more with the help of advanced technology to meet our growing needs, so they are also called as alternate sources of energy.

What is a fuel?

The materials which burn to produce heat energy are called as fuels, e.g. wood, coal, diesel. petrol. LPG. kerosene etc.

In our day to day life fuels are the most important sources of energy.

The choice of the best fuel is made by knowing calorific value of a fuel and its ignition temperature.

Calorific value: The amount of heat produced by burning a unit mass of a fuel is known its calorific value. The unit mass is usually taken as gram. So calorific value of a fuel is also defined as the quantity of heat produced by burning one gram of that fuel completely, e.g. the calorific value of wood is 17kj/g, for coal it is 30kj/g, for kerosene oil it is 48kj/g, for biogas it is 50kj/g, for LPG it is 50kj/g, for methane it is 55kj/g and for hydrogen it is 150kj/g. From these values it is found that hydrogen has the highest calorific value so it is an extremely good fuel.
Ignition temperature: The minimum temperature to which a fuel must be heated so that it may catch fire and start burning is called its ignition temperature or Ignition point. No fuel can burn unless it is heated to its ignition temperature.

What are fossil fuels? How were fossil fuels formed?

A natural fuel formed deep under the earth from the pre-historic remains of plants and animals is called a fossil fuel. Coal, petroleum and natural gas are fossil fuels. These are dug out from the earth. The major portion of our energy demands is being met by these fuels.

How were fossil fuels formed?

The plants and animals which died millions of years ago, were gradually buried deep in the earth and got covered with sediments like mud and sand, away from the reach of oxygen of air.

In the absence of oxygen, the chemical effects of pressure, heat and bacteria converted the buried remains of plants and animals into fossil fuels like coal, petroleum and natural gas.

It should be noted that remains of large plants and animals converted into coal and those of small plants and animals were converted into petroleum and natural gas.

What is coal? What are the uses of coal?

Coal is the most abundant fossil fuel on the earth. It is a complex mixture of compounds of carbon, hydrogen and oxygen and some free carbon. Small amounts of nitrogen and sulphur compounds are also present in coal. It is found in deep coal mines under the surface of earth.

Coal is important because it can be used as a source of energy as such or it can be converted into other forms of energy like coal gas, electricity and oil (synthetic petrol). It provides 27% of the world’s energy.

Uses of coal:

The uses of coal are listed below:

It is used as a fuel for heating purpose in homes and industry.
It is used as fuel in thermal power plants for generating electricity.
It is used to make coke, and then this coke is used as a reducing agent in the extraction of metals.
It is used in the manufacture of fuel gases like coal gas.
It is used in the manufacture of petrol and synthetic natural gas.

Write a short note on petroleum?

it is a dark coloured viscous and foul smelling crude oil. It means rock oil (petra = rock, oleum = oil). It is called petroleum because it is found under the crust of earth trapped in rocks.

Petroleum is a complex mixture of several solid, liquid and gaseous hydro-carbons mixed with water, salt and earth particles. Smal amounts of other compounds of carbon containing oxygen, nitrogen and sulphur are also present in petroleum.

Petroleum can not be used as fuel as such. So before using it as a fuel, petroleum is purified or refined by a process called fractional distillation. This fractional distillation gives us the following fractions which can be used as fuels; petroleum gas, petrol, diesel. kerosene and fuel oil.

Petroleum gas is used as a fuel for domestic heating purpose in the form of liquefied petroleum gas (LPG). Petrol and diesel are used as fuels in automobiles and air traffic. Kerosene is used as a household fuel for heating as well as lighting purpose. Fuel oil is used in industries to heat boilers and in furnaces.

What is LPG (Liquified Petroleum Gas)? What are the advantages of LPG.

On liquification, petroleum gas converts into a liquid called LPG. The main constituent of LPG is butane though it contains small amounts of ethane and propane also. This makes LPG a very good fuel.

LPG is stored in cylinders. It is mainly used for cooking purpose and hence it is also called as cooking gas.

When the valve provided in the cylinder is opened with the help of a regulator, due to decrease in pressure, LPG changes into vapor. This vapour flows to the burner and burns with a blue flame producing a lot of heat.

Advantages of LPG

It is used as a domestic and industrial fuel.
It is used as a fuel in thermal power plants for generating electricity.
Compressed natural gas (CNG) is being used increasingly as a fuel in transport vehicles as being pollution free, it is a good alternative to petrol and diesel.
It has a high calorific value of about 55 kj/g.

What is a thermal power plant and how does it work?

That power plant in which the heat required to make steam to drive turbines is obtained by burning fuels is called thermal power plant.

Working of a thermal power plant.

Coal (fuel oil or natural gas) is burned in a furnace (F) to produce heat.

This heat boils water in a boiler (B) to form steam. The steam formed from the boiling water builds up pressure. ‘The hot steam at high pressure is introduced into a turbine chamber (C) having a steam turbine (T). The steam passes over the blades of the turbine and the high pressure jet makes the turbine to rotate.

The shaft (S) attached to the turbine is connected to a generator (G). When turbine rotates, the shaft also rotates and drives the generator which produces electricity.

The spent steam coming out of the chamber gets cooled and condenses into water which is again sent to the boiler to form fresh steam. This process is repeated again and again and electricity is generated.

What is a hydroelectric Power Plant? What are the advantages and disadvantages of hydroelectric power plants?

The clectricity produced from the kinetic energy of flowing water is called hydro electricity and a plant which generates electricity on a large scale from flowing water is called hydro electric power plant.

Water flowing in a river is collected in a dam, i.e. the kinetic energy of water is converted into its potential energy. Water from the top of the dam is allowed to fall through pipe lines over the blades of a turbine at the bottom of the dam. In this process the potential energy of water changes into its kinetic energy which is transferred to the turbine.

The moving turbine rotates the armature of the generator to generate electricity, i.e. the kinetic energy is converted into electric energy.

The water after running the turbine gets collected in another dam called collecting dam. From this dam it is either let to fall again through a height to produce electricity in the same way or it is sent to canals for irrigating fields.

Advantages of hydroelectric power plants.

The advantages of hydroelectric power plants are given below:

The generation of hydro electricity does not produce any environmental pollution.
Flowing water is a renewable source of energy which will never get exhausted.
The construction of dams on rivers helps in controlling floods.
Hydro electric projects have a very low generation and maintenance cost.
They have a very high efficiency over a considerable load.
They serve as multipurpose projects because they enable us to use their water for irrigation, industrial and domestic use.

Disadvantages of hydroelectric power plants.

The disadvantages of hydroelectric power plants are given below:

The initial investment is very high and gestation period is very long.
These projects cause population displacement, damage the environment and fertile land thereby creating a host of social problems.
Hydro electric generation is not suitable to all rivers and for all areas.

What is biomass? Write a short note on bioenergy?

Biomass: Biomass refers to the plant materials and animal waste used as a source of fuel It includes; (i) Woody source of biomass “including Forest residues, such as dead trees, branches and tree stumps, yard clippings, wood chips, Landscaping residues, wood plantations Industrial wood residue, Waste wood residues”(ii) Non Woody biomass (Oil, sugar, starch) such as: Straw and other harvesting residues from agriculture, residues from food industry and animal droppings etc (iii) Animal and human waste, farm slurry excrements, Slaughter waste, Organic waste from households and industries(sewage, garbage etc).

Bio energy: Bioenergy is the energy derived from the conversion of biomass where biomass may be used directly as fuel, or processed into liquid and gases fuels (biofuels).

Biomass is a renewable source of energy, because it is obtained from plants or animals which can be produced again and again.

Bioenergy is the single largest renewable source of energy today, providing 10% of world primary energy supply.

It plays a crucial role in many developing countries, where use of wood, charcoal, agricultural resides and animal dung are used for cooking and heating in the residential sector, and thus it acts as a basic energy source for them.

Technologies used for generation of bioenergy:

Some of the technologies for generating bioenergy heat and power are:

Solid wood heating installations for buildings.
Biogas digesters for power generation,
Large-scale biomass gasification plants for heat and power.
Co-firing biomass with coal in existing coal-fired power plants

Bio-energy can also be used to generate electricity. Therefore Bioenergy will also play an important role in contributing to heat and electricity demand in the longer term.

Write a short note on ”wood as a fuel”.

Wood is still used as a fuel by burning it in traditional chullahs to cook food and heat water.

However it is disadvantageous in many respects.

The calorific value of wood is 17kj/g which is very low.
Using wood as a fuel leads to deforestation which effects our environment.
Wood as a fuel causes pollution in the form of smoke and harmful gases.
Wood occupies a large area and its transportation is difficult.

What is biogas? How is biogas produced?

Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide produced by anaerobic degradation of biomass in the presence of water but in absence of oxygen. It is a renewable source of energy as it is available continuously from the vast organic wastes.

How is biogas produced?

The process of decomposition of biomass into carbon compounds in the absence of oxygen through a complex series of reactions in presence of water is called Anaerobic degradation. This degradation results into a mixture of gas called biogas. It is also called as Gobar Gas and is produced in a plant called biogas plant.

What is a biogas plant? What are its chief components and how does it work?

The plant where the process of decomposition of biomass into biogas in the absence of oxygen is carried out is called the biogas plant. It is also called the gobar gas plant.

Construction of biogas plant.

A biogas plant consists of a well shaped underground tank (T) called digester tank which is made of bricks and has a dome shaped roof (D) also made of cement and bricks as shown in figure.

The digester is a sealed tank in which there is no air (oxygen). There is a gas outlet (S) at the top of the dome having a valve (V).

The slurry is introduced into the digester tank through the inlet chamber whereas the spent dung slurry is taken out by the outlet chamber. The inlet chamber is connected to a mixing tank while as the outlet chamber is connected to an overflow tank.

Working of a biogas plant.

Cow dung and water are mixed in equal amounts in the mixing tank to prepare slurry. This slurry is fed to the digester tank through the inlet chamber.

The slurry is decomposed for 50 to 60 days in the digester tank by anaerobic bacteria to produce biogas which is collected in the dome.

As more and more biogas collects in the dome, it exerts pressure on the slurry in the digester tank and forces the spent slurry to go into the overflow tank through the outlet chamber.

From the overflow tank the slurry is removed gradually and is used as a manure. To get continuous supply of biogas, fresh dung slurry is added periodically to replace the spent slurry. The biogas is taken out through the outlet (S) and supplied to homes through a network of pipes to be used as a cooking gas.

What are the advantages of biogas?

The important uses of biogas are:

It is used as a fuel for cooking food.
It burns without smoke and does not cause air pollution
It has a high calorific value.
It burns completely leaving no residue behind so it is a clean fuel.
There is no storage problem for biogas as it is supplied to homes directly from the gas plant by pipes.
It is cheaper than most common fuels.
It is also used for lighting.
It is used for generating electricity.
It is a renewable source of energy.

What is wind energy? What is a wind mill and a wind farm?

Moving air is called wind. It has energy due to its motion. So the wind possesses kinetic chergy. It is this kinetic energy which is utilized for doing work.

Wind blows due to uneven heating of earth by the sun in different regions. The wind energy is harnessed by using a wind mill.

Leading users of wind energy include Germany, USA, Denmark and India.

Wind mill: A wind mill consists of a big sized table fan like blades which are fixed over the top of a tall pole in such a way that they are free to rotate. When the fast moving wind strikes the blades, it makes the blades to rotate continuously. The rotatory motion/of the wind mill is then used to do mechanical work through a shaft connected to the rotating blades.

A wind mill is used to:

Pump water
Generate electricity; Electricity is generated from wind by using a specially design arrangement called wind turbine generator. In this arrangement the rotational motion of the wind mill is used to rotate the armature of the generator, which in turn generates electricity.

Wind Energy Farm: The electric power output of a single wind mill is very small and can not be used for commercial purposes. So in order to generate a large amount of electricity, a large number of wind turbines are erected over a big area of land.

The small electricity generated by each wind generator is combined together to get electricity on large scale. Such a cluster of wind mills is called wind energy farm.

The main requirement of a wind energy farm is a site where the wind blows constantly and from a consistent direction. Such as mountain pass, off shore location and islands.

What are the advantages and disadvantages of wind energy?

The advantages and disadvantages of wind energy are given below:

Advantages of wind energy:

It is a non-polluting and eco-friendly source of energy.
It is an important renewable and sustainable source of energy.
The gestation period is low and the power generation starts immediately after commissioning of the wind mill.
The power generation is cheaper and the recurring expenses are almost nil.

Limitations of wind energy:

Wind energy farms can not be established every where.
The wind energy required for generating electricity should be strong and steady to maintain the desired level of generation. The minimum speed required for satisfactory working generator is about 15km/h.
The wind energy farms require a large area of land.
The setting up of a wind energy farm is very expensive.

What is solar energy? What are the advantages and limitations of solar energy?

The sun is the source of all energy. It provides heat and light energy free of cost at a distance of 150×10⁶km from the earth. The energy obtained from the sun is called solar energy. The nuclear fusion reactions taking place inside the sun keep on liberating an amount of heat and light energy. This energy is radiated everywhere place in the form of solar energy.

The sun has been giving this energy at the present rate for 5x 10⁹years and will continue radiating energy at that rate for another 5×10⁹ years.

Since the sun is far away from the earth so a very small amount of solar energy radiated by the sun reaches the outer layer of earth’s atmosphere. Some portion of this energy is reflected back into the space by the atmosphere and little less than hall (about 47%) reaches the earth’s surface. The solar energy which reaches the surface of earth is absorbed by the water bodies. land and plants.

This energy trapped by land and water bodies cause many phenomenon in nature like winds, storms, rain, snowfall and sea-waves etc and plants utilize it to prepare their own food through photosynthesis.

India is fortunate to receive solar energy for greater part of the year. It has been estimated that India receives solar energy about 5000x 10¹⁸ kwh during a year.

Advantages of solar energy:

The advantages of solar energy are given below:

It is available in abundance and that too without cost.
It is pollution free.
It is not exhaustible.

Limitations of solar energy:

The limitations of solar energy are given below:

It is unevenly distributed on the earth and becomes unavailable when sky is overcast with clouds.
A lot of costly equipment and infrastructure is needed to put solar energy to practical
use.
Solar power stations do not match the energy out put of similar sized conventional power stations.
Solar energy can be harnessed only when it is day time.
Large areas of land are required to capture the solar energy.
Solar energy is used to charge batteries. However, these batteries are heavy and need large storage space.
These batteries also need replacement from time to time.
Most of the photovoltaic panels are made up silicon, mercury and other toxic metals.
Pollution in environment, degrade the quality of these cells.

What is solar constant?

The amount of solar energy received per second by one square meter area of a perfectly black surface (exposed perpendicular to the rays of the sun) at an average distance between the earth and the sun is called solar constant. The approximate value of solar constant is 1.4kjs^-1m^-2 or 1.4kWm^-2.

What is a solar cooker? Explain its working? What are the merits and limitations of a solar cooker?

A solar cooker is a device which is used to cook food by utilizing the solar energy. It consists of an insulated metal or wooden box which is painted all black from inside. There is a thick glass sheet cover over the box and a plane mirror reflector is also attached to the box as shown in figure.

The food to be cooked is put in metal containers which are painted black from outside. These metal containers are then placed inside the solar cooker box and covered with the glass sheet.

Working of a solar cooker.

In order to cook food, the cooker is kept in sunshine. The reflector of the solar cooker is adjusted in such a way that it faces the sun.

The sun rays falling on the reflector get reflected towards the top of solar cooker box in the form of strong beam of sunlight. The heat rays get absorbed by the black surface inside of the cooker box. The glass sheet cover traps these heat radiations inside the box and does not allow them to go out. In this way more and more heat rays of the sun get trapped inside the box due to which the temperature in the solar cooker rises to about 100°C to 140°C in two to three hours.

This heat cooks the food kept in the black containers. The food materials like rice, pulses and vegetables can be cooked in this solar cooker. However those foods which need strong heating can not be cooked by this cooker, i.e. baking, frying can not be done by this cooker.

Merits of a solar cooker:

Solar cookers require neither fuel nor attention while cooking.
There is no pollution, no chance of overflowing of food.
The nutritional value of foods does not get destroyed by this method.

Limitations of a solar cooker:

Foods can not be cooked during night or cloudy days.
Cooking takes comparatively longer time.
The direction of reflector has to be changed from time to time to keep it facing the sun.

What is a solar cell? What are the merits and demerits of a solar cell?

A solar cell is a device which converts solar energy directly into electricity. It is also called as solar photo voltaic cell (SPV).

The first solar cell was made of wafer thin sheet of selenium. However, it could convert only 0.7% of solar energy into electric energy. Nowadays silicon is the material used to manufacture solar cells. Their efficiency is about 25%.

A simple solar cell consists of a sandwich of a P-type silicon and an n-type silicon laver. A small piece of wire is soldered into the top of the upper layer and another piece of wire is soldered at the bottom of the lower layer to take the current to the outer circuit.

The cell is covered with a thin glass or transparent plastic cover for protection.

When sunlight falls on the surface of the solar cell, it makes the loosely bound electrons to move due to which an electric current begins to flow. The strength of the current depends upon the brightness of the light and the efficiency of the cell. At present the best designed solar cells can generate 240w/m² in bright sunlight with a maximum efficiency of about 25%.

Solar cell panel: The electric power generated by a single solar cell is quite small. Thus to put solar cells to effective practical use, a large number of such cells are used together in the form of a solar panel. Through a solar cell panel, solar energy is converted into electricity. This electricity is either used for lighting houses and streets at night or it can be used for water pumping and powering remote sensing telecommunication stations.

Merits of solar cell panels:

These are easy to install and maintain.
They do not cause any type of pollution.
They have a long life.

Demerits of solar cell panels:

The initial cost of installing a solar cell panel is high.
The electricity produced by these panels is DC so it can be used to operate DC devices only. However, to operate an AC device, this DC is to be converted first into AC by using inverters which becomes more expensive.
The efficiency of energy conversion is low as compared to other methods of generating electricity.

What is tidal energy? What are the challenges for harnessing it?

The rise and fall of sea water due to gravitational pull of the moon is called tide. This rise of sea water is called high tide while as fall of sea water is called low tide. This rising and falling of sea water occurs twice a day.

These tides provide a large source of energy in the coastal areas of the world. This tidal energy can be harnessed by constructing a tidal dam across a narrow opening of the sea.

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 run the generators to produce electricity.

During the low tide when the level of sea water is low, the sea water stored in the barrage reservoir is allowed to flow out into the sea. This flowing water also turns the turbines which in turn the generators to produce electricity.

This tidal energy is not likely to be a potential source of energy in future because of the following challenges:

There are a few sites around the world which are suitable for building tidal barrages.
The rise and fall of sea water during high and low tides is not enough to generate electricity on a large scale.

What is wave energy? What are the merits and demerits of wave energy?

Ocean waves are a derived source of energy. Due to the blowing of wind on the surface of sea, very fast sea waves move on its surface. Due to their high speed, sea waves have a lot of kinetic energy in them.

Various systems have been designed to use wave energy for commercial production of electricity.

One idea is to set up floating generators in the sea which could run by moving up and down of sea waves.

Another idea is to leave the sea waves move up and down. As the waves move up, the air in the tubes is compressed. The compressed air can then be used to turn the turbine to generate electricity. However, the harnessing of sea waves energy would be a viable proposition only at those places where sea waves are very strong.

Merits of wave energy;

It is a free, renewable and pollution free source of energy.
Wave power projects do not require large land areas.
After extracting energy from waves, sea water is left in a calm state.

Demerits of wave energy;

The power output is of variable nature.
Wave power is expensive with the presently available technologies.
Marine mammal and sea bird population could be affected due to the presence of wave energy structure.

Write a short note on Ocean Thermal Energy Conversion (OTEC).

The process of harnessing the thermal energy of the sea is called OTEC and the devices used for the purpose are called OTEC power plants.

Merits of OTEC

The electric power from OTEC is continuous, renewable and pollution free.
OTEC system transfers nutrients from the unproductive deep waters to the warmer surface thereby enriching the fishing grounds.
It does not have seasonal variations like solar furnaces.

Demerits of OTEC

It requires a lot of capital investment.
Due to small temperature difference between the surface and deep water, the conversion efficiency is low.

Sources of energy class 10 Text Questions and Answers

In this section you will find answers to the text questions of the chapter titled sources of energy in 10th class science book. These answers have been prepared by very experienced teachers. We are very sure that you will find them very useful.

What is a good source of energy?

A good source of energy is the one which:

Performs a large amount of work per unit volume or mass.
Is easily accessible.
Is easy to store and transport and
Is economical.

What is a good fuel?

A fuel is said to be a good fuel, if it has the following characteristics:

It should have a high calorific value.
It should burn without giving out any smoke or harmful gas.
It should have a proper ignition temperature, i.e. the ignition temperature of a fuel
should neither be too low nor too high.
It should be cheap and easily available.
It should be easy to handle, safe to transport and convenient to store.
It should not leave much ash behind after burning.
It should burn smoothly.

If you could see any source of energy for heating your food, which one would you use?

We would use that source which provides uniform heating and heats cleanly without leading to loss in the nutritional value of food.

What are disadvantages of fossil fuels?

The main disadvantages of fossil fuels are:

These are non-renewable sources of energy.
They cause air pollution as they produce smoke on burning.
They produce Carbon dioxide gas on burning which contribute to green house effect and consequently global warming.
They produce gases like CO2 $O2 etc. on burning which mixes with rain water and leads to acid rain, which affects our water and soil resources.

Why we are looking at alternate sources of energy?

Fossil fuels are non-renewable sources of energy which are exhausting day by day. If we continue to use them at the present fast rate, we will be soon deprived of these sources.

Due to this reason we look at the alternate sources of energy so as to save fossil fuels for our future and also provide an alternate sources of energy for future generations.

How has traditional use of wind and water energy been modified for our convenience?

Traditionally wind and water energy has been used directly by converting kinetic energy of water and wind into mechanical energy.

Now wind and water energy has been modified by converting their kinetic energy into electric energy by constructing hydroelectric power plants and by using wind mills.

What kind of mirror be best suited for use in a solar cooker?

A concave mirror is best suited for use in a solar cooker because it reflects and concentrates solar energy from a large area into small area.

What are the limitations of ocean energy?

Ocean energy is the sum total of all the energy that can be obtained from tidal energy, wave energy and ocean thermal energy.

There are several limitations of ocean energy. They are listed below:

Tidal energy depends on the relative positioning of the earth, moon and the sun.
High dams are required to be built to convert tidal energy into electricity.
Very strong waves are required to obtain electricity from wave energy.
To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20°C or more.

What is Geothermal energy? What are the merits and limitations of geothermal energy?

Geothermal energy is the heat energy from hot rocks present a few miles beneath the earth surface (inside the earth).

Geothermal energy is one of those few sources of energy that do not come directly or indirectly from the sun’s energy. It is clean and sustainable.

At some places in the world, the rocks at some depth below the surface of earth are very hot. This heat comes from the fission of radioactive materials which are naturally present in these rocks and continual heat loss from earth formation. The temperature at the core-month boundary may reach over 4000°C. The places where very hot rocks occur at some depths below the surface of the earth are called hot spots and are sources of geothermal energy.

This energy can be harnessed as follows:

The extremely hot rocks present below the surface of the earth, heat the underground water and turn it into steam. As more and more steam is formed between the rocks, it gets compressed to a very high pressure. A hole is drilled into the earth upto the hot rocks and a pipe is put into it. The steam around the hot rocks comes up through the pipe at high pressure. This high pressure steam turns the turbine of a generator to produce electricity.

Sometimes two holes are drilled and two pipes are put into them in the region of hot rocks. Cold water is pumped in through one of the pipes. This cold water is turned into steam by the hot rocks and comes out through the other pipe and then used to generate electricity.

Merits of geothermal energy.

It is most versatile and least polluting renewable source of energy.
It can be harnessed for 24 hours throughout the year.
It is relatively inexpensive.
As compared to solar energy and wind energy, the power generation level of geothermal energy is higher.

Limitations of geothermal energy.

Though as a whole geothermal energy is inexhaustible, a single hole has a limited life span of about 10 years.
Noise pollution is caused by drilling operations at geothermal sites.

What are the advantages and disadvantages of nuclear energy?

Advantages of nuclear energy are:

It produces a large amount of energy from a very small amount of nuclear fuel.
It continuously produces electricity for years together when nuclear fuel is loaded in the nuclear reactor once.
It does not produce gas like CO, which contributes to green house effect or SO2 which causes acid rain.

Disadvantages of nuclear energy are:

The waste products of nuclear reactions are radioactive which keep on emitting harmful nuclear radiations for thousands of years.
Improper nuclear waste storage or disposal can pollute the environment.
There is risk of accidents in nuclear reactors, such accidents lead to the leakage of radioactive materials which are a threat to plant and animal life.
The high cost of installation of nuclear power plant and limited availability of uranium makes the generation of electricity from nuclear reactors limited.

Can a source of energy be pollution free? Explain?

No source of energy is totally pollution free. Only the degree and manner of pollution varies. A source of energy like a solar cell is pollution free but its assembly causes damage to environment.

Is hydrogen a cleaner fuel than CNG. Explain?

Hydrogen is cleaner fuel than CNG because it produces water on burning while as CNG produces CO₂on burning.

Name two energy sources that you would consider to be renewable. Give reasons for your choice.

The two renewable sources of energy are as follows:

Sun: The energy derived from 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 and has capacity to provide energy for ever.

Wind: Wind energy is derived from air blowing with high speed. Wind energy is harnessed by windmills in order to generate electricity. As air blows because of uneven heating of the earth and since heating of the earth will continue forever, therefore wind energy will be available forever.

Give names of two energy sources that you would consider to be exhaustible. Give reasons for your choice.

Two exhaustible energy sources are as follows:

Coal: It is produced from dead remains of plants and animals that remain buried under the earth’s crust for millions of years. Industrialization has increased the demand of coal.

However. coal can not replenish within a short period of time. Hence, it is a non-renewable or exhaustible source of energy.

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, all the existing forests will be consumed and there would be no wood left on the earth. Hence, wood is an exhaustible source of energy.

A solar water heater cannot be used to get hot water on:

A sunny day
A cloudy day
A hot day
A windy day

A Cloudy day.

Which of the following is not an example of a bio-mass energy source.

Wood
Gobar Gas
Nuclear Energy
Coal

Nuclear Energy

Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the solar energy.

Geothermal energy.
Wind energy.
Nuclear energy.
Biomass.