RBSE Class 10 Science Important Questions Chapter 14 Sources of Energy

Rajasthan Board RBSE Class 10 Science Important Questions Chapter 14 Sources of Energy  Important Questions and Answers.

RBSE Class 10 Science Chapter 14 Important Questions Sources of Energy 

Objective Type Questions

Question 1.    
Solar cells are constructed from -
(a) Metals
(b) Alloys
(c) Semiconductors
(d) None of these
Answer:
(c) Semiconductors
 

Question 2.    
For 1 MW generator how much land in hectare is required by wind plant - 
(a) 1 Hectare 
(b) 1.5 Hectare
(c) 2 Hectare 
(d) 2.5 Hectare
Answer:
(c) 2 Hectare 

Question 3.    
The world’s no. 1 country to produce electricity from wind is -
(a) India    
(b) America
(c) Denmark    
(d) Japan
Answer:
(c) Denmark

Question 4.    
For maintaining required speed of turbine, the speed of wind must be greater than -
(a) 15 m/s    
(b) 150 km/hr
(c) 15 km/hr    
(d) 1500 m/s.
Answer:
(c) 15 km/hr    

Question 5.    
Biogas is an ideal fuel. How much percentage of methane gas is present in it ? '
(a) 25%    
(b) 45%
(c) 75%    
(d) 85%
Answer:
(c) 75%

Question 6.    
The main constituent of biogas is -
(a) Methane    
(b) Ethane
(c) Butane    
(d) Hydrogen gas
Answer:
(a) Methane

    

Question 7.    
Reason for liberation of energy in nuclear fission and nuclear fusion reactions is -
(a) Conversion of electric energy
(b) Gravitational energy conversion
(c) Chemical reaction
(d) Conversion of mass into energy
Answer:
(d) Conversion of mass into energy

Question 8.    
The process taking place at sun’s core is -
(a) Nuclear fission
(b) Chemical reaction
(c) Nuclear fusion
(d) None of these
Answer: 
(d) None of these

Very Short Answer Type Questions

Question 1. 
How much solar energy does our country get per year?
Answer: 
Our country receives 5000 trillion kWh of solar energy every year.

Question 2. 
Which property is used in the procedure of solar cookers and solar water heaters?
Answer: 
In all circumstances, the black surface absorbs more heat than the reflective or white surface. This property is used in the procedure of solar cookers and solar water heaters.

Question 3. 
Which metal is used for inter-connection of the cells in the solar panel? 
Answer: 
Silver.

Question 4. 
Write the full name of OTEC power plant.
Answer: 
Ocean Thermal Energy Conversion plant.

Question 5. 
What is a ‘hot spots’?
Answer: 
Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.

Question 6. 
Which type of energy sources are fossil fuels ? Write down any two names of fossil fuels.
Answer:
Fossil fuels are non-renewable conventional source of energy.
Two fossil fuels are: 

• Petroleum
• Coal.

Question 7. 
Write two renewable sources of energy.
Answer: 

1. Solar energy 
2. Wind energy.

Question 8. 
Give two examples of exhaustible energy.
Answer: 

1. Coal 
2. Petroleum.

Question 9. 
Due to which energy source did the industrial revolution became possible?
Answer: 
The use of coal as an energy source made the industrial revolution become possible.

Question 10. 
Why thermal plants are set up near coal and oil fields ?
Answer: 
The transmission of electricity is more efficient than transporting coal or petroleum over the same distance. Therefore, many thermal power plants are set up near coal and oil fields.

Question 11. 
Which plants are called Thermal power plants?
Answer: 
Plants in which thermal energy is generated by combustion of fuel to produce heat energy which is converted into electrical energy are called thermal power plants.

Question 12. 
What is bio-mass?
Answer:
Sources of fuel which are plant or animal products are called bio-mass.

Question 13. 
Which organism are used to generate bio-gas ?
Answer: 
Anaerobic micro-organisms are used.

Question 14. 
Which country is called country of ‘winds’?
Answer 
Denmark is called the country of ‘winds’.

Question 15. 
(a) Name the metal used in preparing solar cell.
(b) Name the heavy atom used in obtaining nuclear energy.
Answer: 
(a) Silicon 
(b) Uranium.

Question 16. 
What is the reason for the level of water in oceans to rise and fall ?
Answer: 
Due to the gravitational pull of moon.

Question 17. 
Solar cell transforms one form of energy into another form. Name these two forms.
Answer: 
Solar cell transforms solar energy into electrical energy.

Question 18. 
What should be observed while selecting a fuel ?
Answer: 

1. How much heat does it release on burning ?
2. Does it produce a lot of smoke ?
3. Is it easily available ?

Question 19. 
What is solar panel ?
Answer 
A large number of solar cells combined in a definite pattern is called solar cell panel.

Question 20. 
The largest wind energy farm has been established in Tamilnadu near Kanyakumari. How much electricity does it generates ?
Answer: 
380 MV.

Question 21. 
Name the device that converts wind energy into mechanical energy.
Answer: 
Wind Mill.

Question 22. 
What do you mean by solar energy tower ?
Answer: 
When solar furnaces are used to generate electricity then it is called solar energy tower.

Question 23. 
What are hot springs?
Answer: 
Sometimes hot water finds outlets at the surface. Such outlets are know as hot springs.

Question 24. 
In which countries geothermal energy based power plants are being widely used?
Answer: 
In New Zealand and United States of America.

Question 25. 
From which source most energy source is derived?
Answer: 
Most energy source are derived the Sun.

Question 26. 
Where can we use solar panel ?
Answer: 

1. These are used for electrification in remote or hilly area.
2. Artificial satellites use solar cell panel to provide electric power for their proper working.

Question 27. 
What are the forms in which energy from the sea water can be obtained?
Answer 

1. Tidal energy 
2. Wave energy
3. Ocean thermal energy.

Question 28. 
Why the reaction of nuclear fusion can not be carried out in a nuclear reactor?
Answer: 
For nuclear fusion very high temperature is required, which is not possible to create such a high temperature in nuclear reactor.

Question 29. 
Name the compounds obtained in the slurry of a biogas plant.
Answer: 
In slurry of biogas plant compounds of nitrogen and phosphorus are found in abundance.

Question 30. 
What is wind farm ?
Answer: 
Place where large number of wind mills are established is called wind farm.

Question 31. 
Which type of energy is present in wind ?
Answer: 
Kinetic energy.

Question 32. 
Among nuclear fission and nuclear fusion reactions, which reaction takes place at high temperature and liberate more energy?
Answer: 
Nuclear fusion.

Question 33. 
On which reaction hydrogen bomb is based ?
Answer: 
It is based on nuclear fusion reaction.

Short Answer Type Questions

Question 1. 
Draw a pie-chart showing the major sources of energy for the energy requirement in India.
Answer: 

Question 2. 
(a) Name two elements that provide nuclear energy.
(b) What is tidal energy ?
Answer: 
(a) Two elements that provide nuclear energy are Uranium and Plutonium.
(b) Tidal energy: 
Due to gravitational pull of mainly moon on the spinning earth, the level of water on the sea rises and falls. This phenomenon is called high and low tides and the difference in sea levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

Question 3. 
By giving the disadvantages of fossil fuels, tell methods to make their use limited.
Answer: 
Disadvantages of fossil fuels -

1. Fossil fuels are non-renewable sources of energy.
2. Burning of fossil fuels results in air pollution.
3. Oxides of carbon, nitrogen and sulphur that are released on burning of fossil fuels are acidic oxides which cause acid rain which affects the water and soil resources.
4. Gases like CO₂, released from burning of fossil fuels increase the green house effect.

Measures to make fossil fuel uses limited:

1. Pollution arising due to burning of fossil fuels can be reduced to some extent by increasing the efficiency of the combustion process.
2. The harmful gases and ashes resulting from combustion can be reduced by using various techniques.

Question 4. 
Name the nuclear reaction which is the source of sun’s energy ? Give the two conditions on the centre of sun due to which this process happens ?
Answer: 
Source of sun’s energy is the nuclear fusion reaction. The estimated temperature of the interior of the sun is 2 x 107 K. At such a high temperature the atoms are continuously colliding with each other on their own and huge amount of energy is released. Thus two conditions due to which sun produces energy are -

1. Excessive high temperature at the centre of sun,
2. Fusion of atoms in the centre.

Question 5. 
What are solar cells ? Name two elements that are used to build solar cell. How much electric energy is produced on keeping a solar cell of 2 cm area in sun ?
Answer: 

1. Solar cell is a device that converts solar energy directly into electrical energy.
2. Silicon and Celenium.
3. Approx. 0.7 watt energy is produced on keeping a solar cell of 2 cm area.

Question 6. 
Make a list of any four forms of energy which we use from morning till night.
Answer:
We use following energies -

1. Heat energy in cooking.
2. Muscular energy for riding a bicycle.
3. Sound energy to call friends.
4. Light energy for lighting house.

Question 7. 
From where do we get the following forms of energy - Light energy, sound energy, muscular energy, burning of LPG to get heat energy ?
Answer:

Types of Energy	Source of Energy
1. Light energy	Thermal electricity, hydro-electricity.
2. Sound energy	In speaking (energy obtained from food) hydroelectricity or thermal electricity.
3. Muscular energy	Food (food material).
4. Heating energy from burning of LPG.	Petroleum gas.

 

Question 8. 
Why bio-gas (gobar-gas) is an excellent fuel? Explain.
Answer: 
Bio-gas is an excellent fuel because -

1. It contains upto 75% methane.
2. It burns without smoke.
3. Leaves no residue like ash in wood, charcoal and coal burning.
4. Its heating capacity is high.
5. Bio-gas is also used for lighting.
6. The slurry left behind is removed periodically and used as excellent manure, rich in nitrogen and phosphorous.

Question 9. 
Draw a sketch of a model to demonstrate the process of thermoelectric and explain it.
Answer:

This is our turbine for generating electricity. The simplest turbines have one moving part, a rotor-blade assembly. The  moving fluid acts on the blades to spin them and impart energy to the rotor. Thus, we see that basically we need to move the fan, the rotor blade, with speed which would turn the shaft of the dynamo and convert the mechanical energy into electrical energy - the form of energy which has become a necessity in today’s scenario. The various ways in which this can be done depends upon availability of the resources. We will see how various sources of energy can be harnessed to run the turbine and generate electricity in the following sections.

Question 10. 
Write the uses of energy from flowing water.
Answer:

1. Energy obtained from flowing water is pollution free.
2. It is a reliable source of energy.
3. Water present in the rivers is in abundance. Hence energy obtained can be cost free.

Question 11. 
How wind energy can be commercially used in power generation ? Explain.
Answer: 
Wind energy is used to generate rotational motion in windmills. To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator. The output of the single windmill is quite small and cannot be used for commercial purposes. Therefore, a number of windmill are erected over a large area, which is known as wind energy farm. The energy out-put of each wind mill in a farm is coupled together to get electricity on commercial scale.

Question 12. 
Explain with reason why charcoal is better source of energy than wood ?
Answer: 
Following reasons are there -

1. Charcoal is easy to transport.
2. Charcoal takes less space and hence easy to-store.
3. Charcoal burns easily.
4. Charcoal burns without producing smoke and has a higher heat generation efficiency.

Question 13. 
What is wind energy ? Write its uses.
Answer: 
Moving air is called wind and the energy possessed by the wind due to its high speed is called wind energy.
Uses of wind energy: Kinetic energy of the wind is used for following purposes -

• By operating water pump to extract underground water.
• For running water boat in river, lake or sea.
• Used to run a flour mill to grind grains.
• For producing electricity.

Question 14. 
Why ‘bio-gas’ is called ‘gobar- gas’?
Answer: 
Cow-dung, various plant material like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give bio-gas. Since the starting material is mainly cow- dung, it is popularly known as ‘gobar-gas’.

Question 15. 
Define solar energy and solar constant.
Answer: 
Solar energy: The heat and light energy emitted by the sun is called solar energy.
Solar constant: The rate at which solar energy arrives at the top of the atmosphere is called solar constant. This is the amount of energy received in unit time on a unit area perpendicular to the sun’s direction at the mean distance of the earth from the sun.

The solar energy reaching unit area at outer edge of the earth’s atmosphere exposed perpendicularly to the rays of the Sun at the average distance between the Sun and earth is known as the solar constant. It is estimated to be approximately 1.4 kJ per second per square or 1.4 kW/m².

Question 16. 
We can not use solar cell panel used to provide energy to the satellites for domestic use. Explain why ?
Ans. Following reasons are there -

1. Solar cell panels are costly.
2. The battery combined in solar cells gives only DC current. Hence only those electric devices can be used which utilize DC current.
3. They provides electricity only till the sunlight is available. They stop working at the time when there is cloudy or rainy day.

Question 17.
A student made a box type solar cooker. We know that it will not work properly. Why this happens ? Write four possible mistakes done during the making and working of the cooker. How much maximum temperature can be maintained in solar cooker ?
Ans.
Following mistakes may be done by the student for preparing the solar cooker:

1. He has not painted the inner part of solar cooker black.
2. He has used plastic cover instead of glass.
3. He has not made it insulated.
4. He has not used black utensils to keep inside the cooker.

Maximum temperature inside the solar cooker box is 140°C.

Question 18. 
Write the main benefits of solar cells. Where are solar cell panels installed?
Answer: 
The principal advantage associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device. Another advantage is that they can be set up in remote and inaccessible hamlet or very sparsely inhabited area in which laying of a power transmission line may be expensive and not commercially viable.

Silicon, which is used for making solar cells, is abundant in nature but availability of the special grade silicon for making solar- cells is limited. The entire process of manufacture is still very expensive, silver used for interconnection of the cells in the panel further adds to the cost. In spite of the high cost and low efficiency, solar cells are used for many scientific and technological applications.

Artificial satellite and space probes like Mars orbiters use solar cells as the main source of energy. Radio or wireless transmission system or TV relay stations in remote locations use solar-cell panels. Traffic signals, calculators and many toys are filled with Solar-cells. Installation of solar panels, the solar-cell panels are mounted on specially designed inclined roof tops so that more solar energy is incident over it.

Question 19. 
Explain nuclear fission reaction.
Answer: 
It is a process in which a heavy nucleus like Uranium, Plutonium, Thorium can be broken by bombarding them with neutrons into lighter nucleus. A large amount of energy is released in this process, if other mass of the original nucleus is just a little more than the sum of the masses of individual products.

In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be part of a self-sustaining fission chain reaction that releases energy at a controlled rate. The released energy can be used to produce steam and further generate electricity.  

Question 20. 
Define and explain nuclear fusion reaction.
Answer: 
Nuclear fusion means joining lighter nuclei to make a heavier nucleus, most commonly hydrogen or hydrogen isotopes to create helium, such as 
²H + ²H → ³He (+ n)
It releases a tremendous amount of energy, according to the Einstein equation, as the mass of the product is little less than the sum of the masses of the original individual nuclei.

Such nuclear fusion reactions are the source of energy in the Sun and other stars.
It takes considerable energy to force the nuclei to fuse. The conditions needed for this process are extreme-millions of degrees of temperature and millions of pascals of pressure.

Question 21. 
What is ‘Charcoal’? Write its characteristics.
Answer: 
When wood is burnt in a limited supply of oxygen, water and volatile materials present in it get removed and the residue that is left behind is called charcoal.
Characteristics of Charcoal are -

1. Charcoal burns without flames.
2.  It is comparatively smokeless.
3. It has a higher heat generation efficiency.

Question 22. 
Write about Hydrogen Bomb.
Answer: 
The hydrogen bomb is based on thermonuclear fusion reaction. A nuclear bomb based on the fission of uranium or plutonium is placed at the core of the hydrogen bomb. This nuclear bomb is embedded in a substance which contains deuterium and lithium. When the nuclear bomb (based on fission) is detonated, the temperature of this substance is raised to 107 K in a few microseconds. The high temperature generates sufficient energy for the light nuclei to fuse and a devastating amount of energy is released.

Question 23. 
Explain the reason why nuclear power plants are not currently in wide- spred use ?
Answer: 
The major hazard of nuclear power generation is the storage and disposal of spent or used fuels - the uranium still decaying into harmful subatomic particles (radiations) improper nuclear-waste storage and disposal results in environmental contamination. Further, their is a risk of accidental leakage of nuclear radiation. The high cost of installation of nuclear power plant, high risk of environmental contamination and limited availability of uranium makes large - scale use of nuclear energy prohibition.

Question 24. 
Explain the problem arises due to the construction of big dams ?
Answer: 

1. A large area of fertile land sink in water at the place of dams.
2. Due to dam construction public has the migrate from their home.
3. Due to deep water of dams on land the organisms and vegetation of that area also spoiled and their destruction happens.
4. Dams can be constructed at some selected place only. Generally hilly areas are best for this purpose.

Question 25. 
What are the limitations of solar cell ? Give their uses also.
Answer: 
Limitations of Solar Cell Panel -

1. Availability of the special silicon for making solar cells is limited.
2. The entire process of manufacture is expensive, the use of silver for interconnection of the cells in the panel makes it more expensive.
3. It has a low efficiency. They can convert only about 25% of the light energy falling on them into electricity.

 Uses of Solar Cells - 

1. Solar cell panel is used in domestic lighting.
2. It is used to run radio and TV sets.
3. Solar cell panel is used to operate water pumps for irrigation of fields.
4. Artificial satellite and space probes like Mars orbiters use solar cells as the main source of energy.
5. Solar cells are used for many scientific and technological applications.
6. Solar cells are used for operating traffic signals, watches, calculators and toys.

Question 26. 
Name the places in India where nuclear power reactors have been installed.
Answer: 
The places in India where nuclear power reactors have been installed are -

Place	State
1. Tarapur	Maharashtra
2. Rana Pratap Sagar	Rajasthan
3. Kalpakkam	Tamil Nadu
4. Narora	Uttar Pradesh
5. Kakrapar	Gujarat
6. Kaiga	Karnataka

 

Essay Type Questions

Question 1. 
Draw a schematic diagram of hydro power plant and explain it.
Answer: 
In order to produce hydel electricity, high-rise dams are constructed on the river to obstruct the flow of water and thereby collect water in larger reservoirs. The water level rises and in this process the kinetic energy of flowing water gets transformed into potential .energy. The water from the high level in the dam is carried through pipes, to the turbine, at the bottom of the dam (see figure). Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy) we would not have to worry about hydro electricity sources getting used up the way fossil fuels would get finished one day.

Question 2. 
What is biogas ? Draw a schematic diagram of biogas plant and describe the gas produced in it. Also give the advantages of biogas.
Answer: 
Biogas:
Cow-dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give bio-gas.

Biogas Plant:
The plant has a dome - like structure built with bricks. A slurry of cow - dung and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber in which there is no oxygen. Anaerobic micro - organisms that do not require oxygen decompose or break down complex compounds of the cow-dung slurry. It takes a few days for the decomposition process to be complete and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. 'Hie bio-gas is stored in the gas tank above the digester from which they are drawn through pipes for use.

Advantages of Biogas:

1. It provides a better and cheaper fuel for cooking, lighting and for power generation.
2. It produces good quality, enriched manure to improve soil fertility.
3. It proves an effective and convenient way for sanitary disposal of human excreta, improving the hygienic conditions.
4. It generates social benefits such as reducing burden on forest for meeting cooking fuel by cutting of tree for fuel wood, reduction in the drudgery of women and children etc.
5. As a smokeless domestic fuel, it reduces the incidence of eye and lung diseases.
6. It also helps in generation of productive employment.

Question 3. 
With the help of a labelled diagram of solar cooker, explain its construction. 
Answer:

A black surface absorbs more heat as compared to a white or a reflecting surface under indentical conditions. Solar cookers and solar water heaters use this property in their working. Some solar cookers achieve a higher temperature by using mirrors to focus the ray of the Sun. Solar cookers are covered with a glass plate. This creates a green house effect inside the solar cooker which further increases the temperature. This makes cooking easy.

Question 4. 
What is wind mill ? Write its construction and uses.
Answer: 
Wind Mill:
The device that converts the wind energy into mechanical energy is called wind mill.

Construction:
In wind mill rotor drives generator through a step up gear box. The components are mounted on a bed plate which is mounted on a pivot at the top of the tower. The two blade rotor is usually designed to be oriented down wind of the tower.

Uses:
The kinetic energy of the wind can be used to do work. This energy was harnessed by windmills in the past to do mechanical work. For example, in a water-lifting pump, the rotatory motion of windmill is utilised to lift water from a well. Today, wind energy is also used to generate electricity. A windmill essentially consists of a structure similar to a large electric fan that is erected at some height on a rigid support.

To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator. The output of a single windmill is quite small and cannot be used for commercial purposes. Therefore, a number of windmills are erected over a large area, which is known as wind energy farm. The energy output of each windmill in a farm is coupled together to get electricity on a commercial scale.

Question 5. 
What are solar panel? Write their limitations and uses.
Answer: 
Solar Panel:
A large number of solar cells combined in a definite pattern called solar cell panel. Solar cell panel provides enough electric power for practical uses. The various solar cells in a solar cell panel are joined together by using connecting wires made of silver metal. This is because silver is the best conductor of electricity. Solar cell panel converts sunlight into d.c. during the day time which is stored by charging a battery connected to it and can be used at night.
A typical cell develops a voltage of 0.5 - 1 V and can produce about 0.7 W of electricity when exposed to the sun.

Limitations:

1. Silver metal is used to connect solar cells which is very costly. Silver has low resistivity so it is used to connect solar cells.
2. The efficiency of solar cells of energy , conversion is very low while manufacturing expenses are very high.
3. Electricity produced by solar cells panels is stored in batteries hence can be used to operate the devices. To operate AC device it has to be converted into AC current.

Uses:

1. Solar cell panels are used in artificial satellites stationed in outer space to provide electric power for their proper working.
2. Solar cells are used for street lighting.
3. These are used for electrification in remote or hilly areas.
4. These are used in railway signals.

Question 6. 
Explain conventional sources of energy.
Answer: 
The sources of energy are being used by us for the last many many years and are produced in the nature years ago are called conventional source of energy. The conventional sources of energy are as follows -
A. Fossil Fuels -
Fossil fuels are the natural fuels formed from the dead remains of the plants and animals which got buried deep under the earth millions of year ago. Examples of fossil fuels are:
1. Coal:
Coal is a complex mixture of carbon and its compounds containing hydrogen, oxygen, nitrogen and sulphur. It is found in deep coal mines under the surface of earth. Coal is a major source of energy.

2. Petroleum:
It is a dark coloured viscous oily compound. It is a general mixture, of several hydrocarbons i.e., compounds of hydrogen and carbon.

3. Natural Gas:
Natural gas is another major source of the energy in our country. Oil and gas fields have been found everywhere on the planet except on the continent of Antarctica. These fields always contain some gases, but this natural gas (methane) does not take nearly as long to form. Natural gas is also found in independent deposits within the ground as well as from other sources too. Methane is a common gas found in swamps and is also the byproduct of animals’ digestive system.

B. Thermal Power Plant:
Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which further runs the turbine to generate electricity. The term thermal power plant is used since fuel is burnt to produce heat energy which is converted into electrical energy.

C. Hydro Power Plants:
Another traditional source of energy was the kinetic energy of flowing water or the potential energy of water at a height. Hydro power plants convert the potential energy of falling water into electricity. Since there are very few water-falls which could be used as a source of potential energy, hydro power plants are associated with dams. In the last century, a large number of dams were built all over the world.

Question 7. 
Explain the alternative or non- conventional sources of energy.
Answer: 
Following are the non-conventional or alternative sources of energy -
1. Solar Energy: The heat and light radiations emitted by the sun is called solar energy.
Solar Energy Devices: A device which gets heated directly by using solar energy or converts it into electricity is called solar energy device. Some devices are solar cooker, solar water heater, solar cell, etc.
2. Energy from the Sea: The energy from the sea can be obtained mainly in three forms -

1. Tidal Energy 
2. Wave Energy
3. Ocean Thermal Energy.

1. Tidal Energy:
Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls. If you live near the sea or ever travel to some place near the sea, try and observe how the sea level changes during the day. This phenomenon is called high and low tides and the difference in sea- levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

2. Wave Energy:
Similarly, the kinetic energy possessed by huge waves near the seashore can be trapped in a similar manner to generate electricity. The waves are generated by strong winds blowing across the sea. Wave energy would be a viable proposition only where waves are very strong. A wide variety of devices have been developed to trap wave energy for rotation of turbine and production of electricity.

3. Ocean Thermal Energy:
The water at the surface of the sea or ocean is heated by the Sun while the water in deeper sections is relatively cold. This difference in temperature is exploited to obtain energy in ocean-thermal-energy conversion plants.
 These plants can operate if the temperature difference between the water at the surface and water at depths up to 2 km is 293 K (20°C) or more.

3. Geothermal Energy:
Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity. The cost of production would not be much, but there are very few commercially viable sites where such energy can be exploited.

4. Nuclear Energy:
Nuclear fission is a process in which the nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low energy neutrons, can be split apart into lighter nuclei. When this is done, a tremendous amount of energy is released. In a nuclear reactor designed for electric power generation, such nuclear ‘fuel’ can be a part of a self- sustaining fission chain reaction that releases energy at a controlled rate. The released energy can be used to produce steam and further generate electricity.