Answer

(b) Sun

Answer

(b) burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere

Explanation

Acid rain happens when rain water mixes with oxides of Carbon, Nitrogen and Sulphur in the atmosphere.

Answer

(d) fossil fuels

Explanation

Coal is the major fossil fuel used in thermal power plants. Along with coal natural gas and petroleum are also used.

Answer

(a) Potential energy possessed by stored water is converted into electricity .

Explanation

Water stored in dams possess potential energy. When it is released it possess potential energy which is used to turn the turbines. Turbines produces electricity.

Answer

(b) Sun

Explanation

Plants produce food by using solar energy. Fossil fuels are produced from dead plants. Hence Sunlight is the source of all energy either directly or indirectly.

Answer

(c) Solar energy

Explanation

In nuclear energy metals like uranium are used which releases harmful rays than can affect the living organisms. In Thermal energy coal is used which releases Sulphur and Carbon-di-oxide and causes air pollution. In the case of geothermal energy the energy is absorbed by the pressure by the heat from the core which can sometimes be extremely hot and dangerous.

Answer

(b) temperature difference at different levels in the ocean

Explanation

Energy from surface is used to boil volatile liquid. Vapors from these are utilized to turn the turbine.

Answer

(c) dispose off spent fuel safely?

Explanation

Nuclear plants produces highly radioactive material. This if released to the environment they pose major threat to living organisms. Hence, disposing the spent fuel safely is a major problem in harnessing nuclear energy.

Answer

(c) Glass sheet

Explanation

Green house effect is due the trapping of heat by the atmosphere. Heat is produced is due to presence of green house gases like $CO_2, SO_2$. In Solar cooker same thing happens. Solar energy trapped is reflected by the glass sheet which make the food cook.

Answer

(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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(c) depends on wind velocity

Explanation

High wind velocity will turn the turbine with at higher speed. This will increase the production of electricity.

Answer

(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.

Answer

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

Answer

(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.

Answer

(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.

Answer

Following are the reason for the need to harness non-conventional sources of energy.

a) Conventional sources are exhaustible source of energy and they will get exhausted in the near future.

b) Non-conventional source of energy did not lead to environmental pollution.

Answer

1 Tidal energy 2 Ocean Thermal energy

Answer

Steps to minimise environmental pollution caused by burning of fossil fuels are as follows.

1. Use con-conventional sources of energy such as hydrothermal and wind energy.

2. Afforestion should be adopted to control air pollution

3. Smokeless appliances should be used to reduce the pollution

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

Answer

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

Answer

Fuel obtained from organic material is called biomass. Following are the methods to obtain bio-energy using biomass.

a) Using firewood as a fuel

b) Preparing cowdung cake and use them as heating source

c) Gobar gas can be produced

d) Electricity can be produced by using gobar .

Answer

Limitations in obtaining energy from wind.

• There will not be continuous and consistent production
• Area required to install wind power mill is large.
• Minimum speed of the wind should be $15 km / hour$.

Answer

Nuclear energy is harnessed in nuclear power plants. It has nuclear reactor, boiler and turbine.

• The nuclear reactor is the place where nuclear fission is carded out. Nuclear fission produces a huge amount of energy.
• Energy produced during nuclear fission is utilized to boil water, so that steam can be generated.
• Steam is utilized to turn the turbines to produce electricity.

Answer

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.

Answer

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.

Answer

Following are the reason for the need to harness non-conventional sources of energy.

a) Conventional sources are exhaustible source of energy and they will get exhausted in the near future.

b) Non-conventional source of energy did not lead to environmental pollution.

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.

Answer

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 animals.

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 recycyle.
• Afforestation

Answer

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 gas.
• Water on the earth gets circulated because of kinetic energy possessed by sun.
• Waves and ocean are formed due to heating of water. Hence sun is indirectly responsible for harnessing Tidal, Wave and Geothermal energy.

Answer

Sources of fuel obtaining from organic material is call as biomass.

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.

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.

Figure 14.4 Schematic diagram of a bio-gas plant

Bio-gas is an excellent fuel as it contains up to 75% methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. Its heating capacity is high. Bio-gas is also used for lighting. The slurry left behind is removed periodically and used as excellent manure, rich in nitrogen and phosphorous. The large-scale utilisation of bio-waste and sewage material provides a safe and efficient method of waste-disposal besides supplying energy and manure.