Here you get the CBSE Class 10 Science chapter 14, Sources of Energy: NCERT Exemplar Problems and Solutions (Part-III). This part of the chapter includes solutions for Question No. 23 to 29 from the NCERT Exemplar Problems for Class 10 Science Chapter: Sources of Energy. These questions include only the Short Answer Type Questions framed from various important topics in the chapter. Each question is provided with a detailed explanation.
NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. All these questions are very important to prepare for CBSE Class 10 Science Board Examination 2017-2018 as well as other competitive exams.
Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Sources of Energy:
Long Answer Type Questions
Question 23. Which is the process used to harness nuclear energy these days? Explain it briefly.
Nuclear fission process is used to harness nuclear energy these days.
The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
In a nuclear fission, the difference in mass, Δm, between the original nucleus and the product nuclei gets converted to energy E at a rate governed by the equation E = Δm c2 , where c is velocity of light.
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 24. How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?
Solar energy can be harnessed directly by using solar cooker, solar hater or solar cells.
In solar cooker the heat energy by sun is used to for cooking purposes. In solar heater, heat energy is used to heat the water. In solar cells it is converted to electricity.
Limitations in using solar energy are:
- Solar energy is not available in night or when the sun is hidden under clouds.
- The domestic use of solar cells for production of electricity is not possible due to high cost.
These limitations can be overcome by following ways:
- First limitation can be overcome by converting solar energy into electrical energy and storing them for future use.
- Second limitations can be overcome by taking certain steps by government to reduce price of solar cells.
Question 25. Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one non-conventional source of energy.
Conventional Sources of Energy
- Fossil fuels
- Hydro-electric Power Plant
- Thermal Power Plant
Non-Conventional Sources of Energy
- Solar Energy
- Tidal Energy
- Nuclear Energy
- Ocean Thermal Energy
Harnessing nuclear energy:
Nuclear energy is a non-conventional source of energy and can be harnessed by a process called nuclear fission. 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 if the mass of the original nucleus is just a little more than the sum of the masses of the individual products. The fission of an atom of uranium, for example, produces 10 million times the energy produced by the combustion of an atom of carbon from coal. 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 26. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?
The population of the world is increasing at a very rapid rate due to which demands for energy is increasing day by day. As, fossil fuels like coal, petroleum, are present in a limited amount which and are likely to finish one day so the need for alternative sources of energy is essential.
Use of conventional sources of energy (coal, petroleum etc.) causes pollution. To reduce pollution use of non-conventional sources of energy is essential.
The energy from the sea energy be harnessed from the sea in different ways
Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in 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.
The kinetic energy possessed by huge waves near the seashore can be trapped 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 has been developed to trap wave energy for rotation of turbine and production of electricity.
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 20 K (20°C) or more. The warm surface-water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of generator. The cold water from the depth of the ocean is pumped up and condense vapour again to liquid. The energy potential from the sea (tidal energy, wave energy and ocean thermal energy) is quite large, but efficient commercial exploitation is difficult.
Question 27. What are the environmental consequences of using fossil fuels? Suggest the steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy causes global warming.
Followings are the environmental consequences of using fossil fuels:
- The burning of fossil fuels produces greenhouse effect of gases like carbon dioxide and results in global warming.
- The burning of fossil fuels also releases oxides of nitrogen and sulphur that are released by burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resources.
The steps to minimize the pollution caused by various sources of energy including non-conventional sources of energy causes global warming.
Pollution caused by combustion of coal, petroleum (conventional sources) and biomass (non-conventional sources) can be reduced by increasing the efficiency of the combustion process and using various techniques to reduce the escape of harmful gases and ashes into the surroundings.
The effect of green house gases released by burning of fossil fuels and biogas can be minimized by planting more trees.
Pollution due to nuclear waste can be minimized by properly disposing nuclear wastes.
Question 28. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Yes, I agree by the statement that energy from various sources is considered to have been derived from the sun, reasons for which are:
Wind Energy: As we know that warm air rises up and cold air settles down. By similar principal, due to uneven heating of the earth’s surface by the sun rays at two different adjoining places a pressure difference is created and wind is produced.
Wave energy: Strong winds are generated due to the sun and the waves are generated by strong winds blowing across the sea.
Ocean thermal energy: The difference between the water at the surface and water at depth in seas and oceans is due to the sun.
Energy from fossil fuels: Fossil fuels (coal, petroleum etc) are formed when large plants and ancient creatures are buried deep inside the earth crust under the effect of a lot of pressure and heat.
Solar energy: The phenomenon of photoelectric effect (generation of electricity by light) is possible only in the presence of sun.
Bio-mass: Plants converts the solar energy into chemical energy with the help of inorganic substances (i.e. air, water etc). These plants are consumed by plants and animals and produce wastes from which energy is obtained.
Energy from flowing water: Water from sea and rivers evaporate and fall at different places of the earth as snow and rainfall. This water collected in a dam and when allowed to flow rotates turbine of generator and electricity is produced.
Question 29. What is bio-mass? Explain the principle and working of a biogas plant using a labelled schematic diagram.
Biomass refers to those living and non-living organic materials that can be used as sources of energy in the form of fuel. Some examples of biomass fuels are biogas, wood, crops, and organic garbage. The chemical energy in biomass is released as heat on burning.
Bio-mass refers to the organic fuel obtained from plants and animal wastes like wood, cow-dung, residue after harvesting the crop, vegetable waste and sewage, etc. It has been used as a fuel for a long time. These fuels, however, do not produce much heat on burning and a lot of smoke is given out when they are burnt.
When substance likes cow-dung, vegetable waste etc undergoes anaerobic (in absence of air) decomposition then these complex substances are broken down into simpler substances and gases like methane, Carbon dioxide etc are produced.
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. The bio-gas is stored in the gas tank above the digester from which they are drawn through pipes for use.