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Sources of Energy Class 10 Notes, CBSE Chapter 14 Science, Question Answers

Sources of Energy Class 10 Notes -CBSE Class 10 Science Sources of Energy Chapter 14 complete explanation and Notes Topics covered in the lesson are Source, Solar cell, Types of natural resources, energy from the sea, Fossil fuels, Ocean thermal energy etc. Given here is the complete explanation of the chapter, along with all the important questions and NCERT solutions to book questions have also been provided for the ease of students

 

Class 10 Science Notes Chapter 14 - Sources of Energy

 

sources of energy

 

Table of content

  1. Source
  2. Types of natural resources
  3. Fossil fuels
  4. Hydel power plant
  5. Biomass
  6. Solar energy
  7. Solar cooker
  8. Solar cell
  9. Energy from the sea
  10. Ocean thermal energy
  11. Geothermal energy
  12. Nuclear energy
  13. NCERT book solutions
  14. Solar water heater

 

See Video for Explanation and Summary of the Lesson

 

Source of Energy

Anything that provides us energy is called a source of energy. We need energy for various purposes. So, we need a source of energy that provides us with this energy. Some sources of energy are more efficient in comparison to others, while some sources of energy are cleaner as they do not contribute to pollution. Examples of sources of energy are solar energy, wind energy, hydel energy, biofuels, and geothermal energy.

A source of energy can be classified into renewable and non-renewable source. We will discuss this in detail further.

 

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Types of natural resources

  1. Renewable (non-conventional resources): These are resources that can be used again and again or we can say that these resources will not finish easily and will last for a long time.

 

For example: solar energy, water, air.

  1. Non-renewable resources (conventional): These are the resources that can not  be used  again and again because if they get exhausted, they will take a lot of time to form.

 

For example fossil fuel, etc.

 

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Fossil fuels

 

fossil fuels

 

They are formed when dead plants and animals get buried under the earth over millions of years and due to high pressure and temperature, they get transformed into fossil fuels. They are non-renewable resources, so their wise use is recommended.

For example: coal, petroleum and natural gas.

Coal: It is a sedimentary rock that burns. It mainly contains carbon, hydrogen and oxygen. It also has some quantity of nitrogen and sulphur.
Different types of coal:

  1. Peat
  2. Lignite
  3. Bituminous
  4. Anthracite

Destructive distillation is a process when any substance is heated in the absence of air. Products obtained on a destructive distillation of coal are coke, coal tar, coal gas, and ammoniacal liquor.

  1. Coke: it is used as a reducing agent in metallurgy and as a fuel.
  2. Ammoniacal liquor: it is converted into ammonium sulphate by absorbing dilute sulphuric acid and ammonium sulphate is an excellent fertilizer.
  3. Coal tar: it is used for surfacing roads and also as a source of different aromatic compounds.
  4. Coal gas: it is a mixture of hydrogen, methane and carbon monoxide. All these gases provide heat when burnt. It is a good fuel (cooking gas).
  5. Natural gas: it has mixtures of alkanes i.e. 80% methane, 7%ethane, 6% propane and 4%butane.
  6. It occurs deep in the earth’s crust with petroleum deposits.
  7. Propane and butane are separated from natural gas and are liquefied under pressure to form LPG (used as a domestic and industrial fuel).
  8. CNG (Compressed Natural Gas ) having main constituent methane is also used as a fuel in vehicles and in industries.

 

Energy and environment:

  1. Increasing rate of industrialization.
  2. Increasing demand for luxurious items.
  3. Increase in demand for entertainment facilities.
  4. Increase in demand for various modern techniques of agriculture and also the use of chemicals like pesticides, fertilizers, etc.
  5. Petroleum: the name ‘petroleum’ means rock oil  (petra: rocks; oleum:oil). It is called petroleum because it is found in the crust of the earth, trapped in rocks. A range of fossil hydrocarbons that are found as gasses, liquids and solids beneath the earth's surface. The two common forms of petroleum are crude oil and natural gas.

 

Crude oil: It is a complex mixture of alkane hydrocarbons with water and earth particles. The final stage of refining involves the removal of impurities such as sulphur compounds.

When a fuel containing sulphur is burnt, the sulphur in it turns into sulphur dioxide which is an acidic gas. So, it is to be purified or refined before it can be used for specific purposes. The process of separating crude petroleum oil into more useful fractions is called refining.The refining of petrol is done by the process of fractional distillation. Refining is needed to make sure that all the oil is turned into useful products.

Cracking also occurs during the refining process of petroleum. The process of breaking bigger hydrocarbon molecules into smaller hydrocarbon molecules by heating in the presence of a catalyst is called cracking. The refining of petroleum or separation of petroleum into different components is based on the fact that the different compounds of crude oil have different boiling point ranges.

The fraction of petroleum having highest boiling point range is collected in the lowest part of the fractionating tower. The fraction having the lowest boiling point range is collected in the topmost part of the tower. Such a process of separation of different fractions of petroleum from crude oil is called fractional distillation. Otherwise, if we discuss about fuels we can define them as:

Fuels: anything that provides us energy is called fuel. Fuels can be solid, liquid and gases.

Solid fuel example : coal
liquid fuel example : kerosene
Gas fuel example : LPG

 

fuels

 

Characteristics of an ideal fuel are as follows:

  1. It should be cheap.
  2. It should be easily stored.
  3. It should have high calorific value.
  4. It should have proper ignition temperature.
  5. It should not leave any residue.

Uses of fossil fuels:

  1. They are used in generating electric energy in thermal power plants.
  2. Natural gas is also used in thermal power plant.
  3. Petroleum byproducts like paraffin wax, lubricating oil, etc are used for different purposes.

 

Disadvantage of fossil fuels :

  1. They are non renewable.
  2. They produce a lot of carbon dioxide that causes the greenhouse effect.
  3. They produce a lot of smoke.

 

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Hydel power plant

It is the arrangement in which the kinetic energy of flowing water is transformed into electric energy. The electric energy thus generated is called hydroelectricity.

 

powerhouse

 

In hydroelectric power plant, water is stored at a height in reservoirs provided with gates. These gates are opened and water is allowed to flow where its potential energy gets converted into kinetic energy. This energy rotates the blades of turbines which is further coupled to a generator. When the coil of the armature of the generator rotates, electric energy is produced.

Advantages of hydel energy

  1. Water is free of cost.
  2. These plants are pollution free.
  3. Construction of dams helps to control floods.

 

Limitations of hydel energy

  1. For running these plants, a large amount of water is required.
  2. Construction of dams needs a lot of investment.
  3. Construction of dams affects a lot of flora and fauna.

Conventional source of energy

 

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Biomass

Biomass: It is the waste material produced by living beings and the dead.

 

types of biomass

 

Biogas: It is a mixture of methane, carbon dioxide, hydrogen and traces of hydrogen sulphide. It is produced due to anaerobic fermentation of biomass. Plant that is used is: bio gas plant as shown in the figure:

 

biogas plant

 

In this, cattle dung and slurry is mixed in equal proportions and is fed into the digester tank where it is left for a few days. In the digester, fermentation takes place that is bacteria or microorganisms produce enzymes, that in anaerobic condition start converting it into simple substance.
Along with the simple substances, biogas is produced which starts collecting in the dome. As the volume of gas collected increases, it pushes the used slurry into overflow tank and with time, it is filled again with slurry and the process goes on occurring. We can take the gas out from the pipe and use it for various purposes.

Advantage of using biogas as fuel:
1.   The spent slurry is used as manure.
2.   It is used for domestic cooking.
3. It is eco friendly.
4. It leaves no residue.
5. It is also used for illumination purpose. 

Wind energy: Moving air is called wind. It is produced due to uneven heating of earth's surface by the sun. The energy can also be used to generate electricity as explained below.

The setup that is used is wind energy farms as shown :

 

wind energy farms

 

The farms have a number of windmills which are actually poles that bear blades. The shaft of wind mill is connected to the shaft of the armature of the generator. When the fast moving wind rotates the blades of windmill its shaft rotates, armature rotates and hence, electricity is produced which is further used for various purposes.

Advantages of using wind energy:

  1. It is a natural renewable resource.
  2. It is eco friendly.

 

Disadvantages:

  1. It can not be established everywhere.
  2. It requires a large area.  
  3. It is an expensive project.  
  4. Wind does not blow all the time so, wind energy can not  be produced every time.  
  5. Minimum speed of wind required is 15km per hour.

 

wind energy

 

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Solar energy
It is the energy that we get from the sun. It is a renewable source. This energy helps in keeping the temperature of earth hotter, causes air currents in the atmosphere and causes water cycle and also helps in photosynthesis.

 

solar energy

 

Solar constant: It is the total energy that falls on 1metre square area in 1 second.

Limitations of solar energy

  1. It falls in diffused form.
  2. It is not available all the time.
  3. It is not available at a constant rate.
  4. It is not available at night.
  5. It is not available at all places.

 

solar system

 

Solar heating devices : They are the devices that work on solar energy like:

 

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Solar cooker

It is a device that is used to cook food with the help of sunlight. It is of two types i.e: Box type and concave reflector type.

Box type solar cooker consist of following as shown:

Use of reflector: It reflects the rays that do not fall normally so that more and more rays enter the solar cooker.

Use of glass: It allows infrared rays to enter but does not allow them to escape. So, as a result, they get trapped and the temperature is maintained in the solar cooker.

Black colour: As black color is a perfect absorber of heat, the sun rays falling on the reflector are reflected and the glass sheet allows them to enter but does not allow them to escape. Inside it four bowls can be kept at a time in which we can make dal, rice, khichdi, etc

Limitations

  1. It can not be used to bake, fry, or make chapattis.
  2. It is time consuming.
  3. It can not be used at night.
  4. It can not be used during rainy or humid weather.
  5. Concave reflector type: It is as shown in the figure. The advantage of it is that the concave reflector reflects all the rays falling on it, converging at the focus. At focus, a high temperature can be achieved and it can be used for making chapatis, frying and baking.

 

Advantages of solar cooker 

  1. It is eco friendly
  2. It saves fuel
  3. Nutrient value of food is retained
  4. It is free of cost as no fuel is used

 

concave reflector

 

  1. It is eco friendly
  2. It saves fuel
  3. Nutrient value of food is retained
  4. It is free of cost as no fuel is used

 

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solar water heater

 

Solar water heater

It contains an insulated box, painted black from inside. In it, copper tubes are placed in the form of coils. Tubes are also painted black from outside. The box is covered with a glass sheet to prevent loss of heat. The two ends of the tube are joined to a storage tank.
Fresh tap water enters the tank through pipes and then it flows through a copper tube in  box and when flowing through a tube, it gets heated up and is collected at the top of the tank as density of hot water is always less as compared to that of cold water.

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Solar Cell

It is the cell that converts solar energy into electric energy. It is made of semiconductors like germanium etc. In it, many solar cells are connected in series to each other by means of wires to form solar cell panel and to produce desired voltage. The electric energy thus produced is used to do various tasks as shown:

 

solar cell

 

Advantage of solar cells :

  1. It is a safe, cheap, noiseless source of energy.
  2. It has very low maintenance cost. 
  3. It is suitable for portable devices.

 

Uses of solar cells :

  1. It is used for providing electricity
  2. It is used in street lights
  3. It is used in calculators
  4. It is used to provide light where otherwise availability of light is not possible like in remote areas.

 

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energy sea

 

Energy from the sea

The periodic rise or fall in the water level occurring twice in each lunar day is called tide. High tides occur on new moon and full moon day otherwise there are low tides. These tides are formed  due to the gravitational force of the moon and the sun on ocean water. The difference in the level of tides results in ocean thermal energy. For harnessing its energy, tidal dam is constructed and the ocean water is trapped by a barrier.
This water is then allowed to fall down on water turbine, converting kinetic energy of flowing water into mechanical energy and then to electrical energy. The difference in the level of tides should be about 3 metres. Tides are not formed at all times.

 

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Ocean thermal energy

 

ocean thermal energy

 

As the solar radiations fall directly on the upper layers of the ocean, they heat up the upper layers and the lower layers remain comparatively cooler. So, if difference of approximately 20 degree celsius exists, then OTEC plant can be used. In this, the warm surface water is used to boil ammonia. The vapours of this ammonia are then used to run turbines and hence, generators. This system can be operated 24 hours a day. Advantage of OTEC plant over tidal energy is that we don’t have to wait for the tides to form.

 

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Geothermal energy

 

geothermal energy

 

It is the thermal energy generated by earths core.Under the earths surface, hotspots are present at certain places. These hotspots have water and hot rocks called magma. Actually, the deeper regions are quite hot. This heat melts the rock that is called magma. This magma is pushed up due to some geological changes. This magma collects below the surface of earth called hotspots.The underground water is in contact with hot spots and turns into steam. This steam is trapped between rocks. Due to this, it gets compressed with high pressure and this steam is extracted by sinking pipes through holes drilled up to hot spots. Then this steam comes up with high pressure and it gets utilized to turn the turbine of the electric generator.

Advantage of geothermal energy

  1. It can be operated round the clock.
  2. It is an eco friendly source of energy.
  3. It is a renewable source of energy.
  4. The cost of operating it is half the cost of producing electricity by burning coal.

 

Limitations of geothermal energy are as follows:

  1. It is difficult to locate hotspots.
  2. Hotspots are not present everywhere.

 

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Nuclear energy

 

nuclear fission

 

It is the energy  possessed by the nucleus of an atom. It is the process due to which energy of a nucleus is released. Types of nuclear reactions :

  1. Nuclear fission: It is the reaction in which energy is released when a bigger nucleus splits into two or more lighter nuclei i.e. the energy released per fission is 200Mev. But generally, the fission reaction is uncontrolled due to which its energy can not be used for constructive purpose but if we want to control it, we carry out the reaction in a nuclear reactor which is designed in such a way that controlled fission takes place.
  2. Nuclear reactor: It is a device which is used to control an uncontrolled fission. In it, the controlling rods are used which also absorb extra neutrons so that reaction does not occur as a chain uncontrolled reaction. These rods are made of cadmium and boron. Also, in it heavy water is used that slows down the speed of fast moving neutrons so that they can collude effectively with fuel rods. Coolant is used that absorbs the heat energy liberated due to the reaction. Most of the times liquid sodium is used.

 

nuclear reactor

 

Safety measures to be taken are as follows

  1. Lead containers must be used for keeping radioactive elements.
  2. The workers must wear lead aprons and specially designed suits.
  3. They are well insulated in a chamber made of glass.

Hazards of nuclear radiations

  1. Disposal of nuclear waste is a big problem.
  2. There is a risk of accidental leakage. 
  3. It has high cost of installation.
  4. Limited availability of nuclear fuel like uranium.

 

Advantage of nuclear energy

  1. It produces tremendous energy.
  2. There is no need to feed the fuel again and again. Fuel once fed is used for a much longer period.

 

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NCERT Book solutions

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.

Ans. (b) A cloudy day

 

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

Ans. (c) Nuclear energy

 

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) biomass.

Ans. (c) Nuclear energy

 

4. Compare and contrast fossil fuels and the Sun as direct sources of energy.

Ans. 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 get exhausted, their 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.

 

5. Compare and contrast biomass and hydroelectricity as sources of energy.

Ans. Biomass and hydro-electricity both are renewable sources of energy. Biomass 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 biomass.
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.

 

6. What are the limitations of extracting energy from-
(a) the wind?
(b) waves?
(c) tides?

Ans. Wind energy is harnessed by windmills. One of the limitations of extracting energy from wind is that a windmill requires wind speed of more than 15 km/hr 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 Earth.

 

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?

Ans. (a) The source of energy that replenishes in nature is known as a renewable source of energy. Sun, wind, moving water, biomass, 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. Biomass is one of the inexhaustible sources of energy.
Yes. The options given in (a) and (b) are the same.

 

8. What are the qualities of an ideal source of energy?

Ans. An ideal source of energy must be:
I. Economical
II. Easily accessible
III. Smoke/pollution free
IV. Easy to store and transport
V. Able to produce huge amount of heat and energy on burning

 

9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

Ans. 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 a 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.

 

10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Ans. 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 greenhouse 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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