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ScienceClass 10CBSE

1. For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is (a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid (b) The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron, when placed inside the coil (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Soln: Answer is (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet Explanation: Solenoid behaves like Bar magnet, therefore the pattern of the magnetic field associated with the solenoid is same as the pattern of the magnetic bar around a bar magnet.

ScienceClass 10CBSE

1. Choose the incorrect statement from the following regarding magnetic lines of field (a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points (b) Magnetic field lines are closed curves (c) If magnetic field lines are parallel and equidistant, they represent zero field strength Relative strength of magnetic field is shown by the degree of closeness of the field lines

Answer is (c) If magnetic field lines are parallel and equidistant, they represent zero field strength Explanation: Option c) is incorrect because parallel lines of magnetic field represent uniform magnetic field.

ScienceClass 10CBSE

1.      Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.

Soln: Energy from various sources is considered to have been derived from the sun. Following points can justify the statement. Energy from fossils fuels are indirectly harnessed from sunlight because. Plants trap sunlight to produce food which ultimately makes biomass. Biomass gets converted to fossil fuels. Biomass will be helping in obtaining wood and gobar Water on the earth gets circulated because of kinetic energy possessed by Waves and ocean are formed due to heating of Hence sun is indirectly responsible for harnessing Tidal, Wave and Geothermal energy.

ScienceClass 10CBSE

1. What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.

Soln: Following are the consequences of using fossil fuels. Global warming will result due to increase in the level of Carbon-di-oxide, Sulphur oxides causes acid rain Burning of fossil fuels will result in accumulation of smog in big cities which will result in decreased visibility Air pollution leads to health hazrds to humans and Steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy. Use of public transport Use of vehicles like electric bikes and bi-cycle that can reduce air pollution Adopting 3R’s policy- reduce, reuse and Afforestation

ScienceClass 10CBSE

1. Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea in different ways?

Soln: Following are the reason for the need to harness non-conventional sources of energy. Conventional sources are exhaustible source of energy and they will get exhausted in the near Non-conventional source of energy did not lead to environmental Energy can be harnessed from the sea in following ways 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. As you can guess, the locations where such dams can be built are limited. Wave energy 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. 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.

ScienceClass 10CBSE

1.      Make a list of conventional and non-conventional sources of energy. Give a brief description of harnessing one nonconventional source of energy.

Soln: Conventional sources of energy are coal, petroleum, fire wood and tidal energy. Non-conventional sources are Solar energy, nuclear energy, Biogas, Tidal energy, Ocean thermal energy, wave energy etc. Methods to harness Non-conventional sources of energy. Solar Energy can be harnessed by using solar cookers, solar water heaters, solar cells and solar panels. Nuclear power can be converted to electric energy with the help of nuclear reactors. 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. 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.

ScienceClass 10CBSE

1.      How can solar energy be harnessed? Mention any two limitations in using solar energy. How are these limitations overcome?

Solar Cookers and solar water heaters: A black surface absorbs more heat as compared to a white or a reflecting surface under identical conditions. Solar cookers (Fig. 14.6) and solar water heaters use this property in their working. Some solar cookers achieve a higher temperature by using mirrors to focus the rays of the Sun. Solar cookers are covered with a glass plate. Solar energy trapped is reflected by the glass sheet which make the food cook. Solar Cell 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. A large number of solar cells are, combined in an arrangement called solar cell panel (Fig. 14.7) that can deliver enough electricity for practical use. The principal advantages 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 hamlets or very sparsely inhabited areas in which laying of a power transmission line may be expensive and not commercially viable.

ScienceClass 10CBSE

What is biomass? What can be done to obtain bio-energy using biomass?

Fuel obtained from organic material is called biomass. Following are the methods to obtain bio-energy using biomass. Using firewood as a fuel Preparing cowdung cake and use them as heating source Gobar gas can be produced Electricity can be produced by using gobar .

ScienceClass 10CBSE

1.      What are the limitations in obtaining energy from wind?

Limitations in obtaining energy from wind. There will not be continuous and consistent production Area required to install wind power mill is Minimum speed of the wind should be 15 km/hour.

ScienceClass 10CBSE

1.      Mention three advantages of a solar cell?

Advantages of a solar cell is as follows. Solar cells are the source of renewable energy Solar cells do not produce pollution Solar cells need minimum maintenance

ScienceClass 10CBSE

1.      Write two different ways of harnessing energy from ocean.

Tidal energy Ocean Thermal energy

ScienceClass 10CBSE

1.      What is the role of a plane mirror and a glass sheet in a solar cooker?

Soln: Plane mirror reflect the sunlight thereby increasing the intensity of solar energy. Glass sheet prevents heat escape from solar cooker.

ScienceClass 10CBSE

1. What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?

Steps to minimise environmental pollution caused by burning of fossil fuels are as follows. Use con-conventional sources of energy such as hydrothermal and wind Afforestion should be adopted to control air pollution Smokeless appliances should be used to reduce the pollution

ScienceClass 10CBSE

1.      Why is there a need to harness non-conventional sources of energy? Give two main reasons.

Following are the reason for the need to harness non-conventional sources of energy. Conventional sources are exhaustible source of energy and they will get exhausted in the near Non-conventional source of energy did not lead to environmental

ScienceClass 10CBSE

1. Choose the incorrect statement (a) We are encouraged to plant more trees so as to ensure clean environment and also provide bio-mass fuel (b) Gobar-gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen (c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash Bio-mass is a renewable source of energy

Soln: Answer is (c) The main ingredient of bio-gas is ethane and it gives a lot of smoke and also produces a lot of residual ash Explanation: Main product of a biogas is methane. It burns with less smoke and did not produce residual ash.

ScienceClass 10CBSE

1. Choose the incorrect statement regarding wind power (a) It is expected to harness wind power to minimum in open space (b) The potential energy content of wind blowing at high altitudes is the source of wind power (c) Wind hitting at the blades of a windmill causes them to rotate The rotation thus achieved can be utilised further (d) One possible method of utilising the energy of rotational motion of the blades of a windmill is to run the turbine of an electric generator

Answer is (b) The potential energy content of wind blowing at high altitudes is the source of wind power. Explanation: Wind power runs by kinetic energy of the wind. Hence statement b) is wrong.

ScienceClass 10CBSE

1. In a hydroelectric power plant more electrical power can be generated if water falls from a greater height because (a) its temperature increases (b) larger amount of potential energy is converted into kinetic energy (c) the electricity content of water increases with height more water molecules dissociate into ions

Soln: Answer is (b) larger amount of potential energy is converted into kinetic energy

ScienceClass 10CBSE

1. Choose the correct statement (a) Sun can be taken as an inexhaustible source of energy (b) There is infinite storage of fossil fuel inside the earth (c) Hydro and wind energy plants are non polluting sources of energy Waste from a nuclear power plant can be easily disposed off

Soln: Answer is (a) Sun can be taken as an inexhaustible source of energy Explanation: Fossil fuel is an exhaustible source. Hydro and wind energy plants can have large environmental impacts by changing the environment and affecting land use, homes, and natural habitats in the dam area. Disposing off waste from a nuclear power plant is the major issue faced by nuclear plant.

ScienceClass 10CBSE

1. The power generated in a windmill (a) is more in rainy season since damp air would mean more air mass hitting the blades (b) depends on the height of the tower (c) depends on wind velocity can be increased by planting tall trees close to the tower

Soln: Answer is (c) depends on wind velocity Explanation: High wind velocity will turn the turbine with at higher speed. This will increase the production of electricity.

ScienceClass 10CBSE

1. The main constituent of biogas is (a) methane (b) carbon dioxide hydrogen (d) hydrogen sulphide

Soln: Answer is (a) methane Explanation: Methane gas is the main product of biogas. Around 70% of the gas produced is methane and remaining will be ammonia, carbon-di-oxide.

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