Energy Resources and Environmental Pollution, Physics tutorial

Physics and Environment:

Environmental physics is an application of laws and methods of physics to offer explanation of natural environment. There are several environmental problems facing mankind. Few of these problems are ozone layer depletion, global warming, energy crisis, nuclear and electronic waste disposal complications. Further are air, soil, water and thermal pollution. Such problems and their solutions can be understood from viewpoint of physics. This describes why environmental physics is very significant discipline. Ultimate aim of environmental physicist is to recognize these issues and give solutions using principles and methods of physics.

Air Pollution:

Air is polluted when fossil fuel is burned. Fossil fuels comprise coal, oil, gas and fire-wood. Air pollution can result from burning fossil fuel in cars, in industrial furnaces for smelting, and in electric producing plants. The circumstance is worse if burning occurs so rapidly that combination is incomplete. That is why internal combustion engines of automobiles are particularly hostile to environment.

Due to incomplete nature of combustion in automobile engines, more noxious gases are generated. Even when combustion is complete, condition still remains bad as carbon-dioxide (CO2) released in atmosphere absorbs few of the natural infrared radiations emitted by warm earth (and prevents them from escaping). Resulting build up of atmospheric CO2 and consequent heating of atmosphere is called as green house effect. Scientists have estimated that green house effect is able to raise average temperature of atmosphere by several Celsius degrees within this century. Such increase in temperature of the atmosphere is of serious concern because of the fact that it can cause shift in rainfall patterns and melt polar ice caps. Huge amounts of water resulting from melted polar ice caps will be dumped in oceans thus raising sea-level and flooding the low-land areas. There is, thus, urgent requirement for humans to limit rate at which fossil fuel is burned.

Thermal Pollution:

Every heat engine exhausts heat to environment. Automobiles and power plants are good instances of heat engines. Electricity-generating power plants utilize a heat engine to convert thermal energy in electrical energy. Exhausted heat is usually absorbed by the coolant like water.

The basic thought behind heat engine is that thermal energy can be transformed in mechanical energy only when heat is permitted to flow from a high-temperature reservoir to low-temperature reservoir. In the procedure, some of heat can then be utilized to perform mechanical work. Efficiency η of heat engine is provided by

η = 1 - QL/QH

Here QH is heat input at high temperature TH, and QL is heat condemned at low temperature TL. For the ideal Carnot engine, heat Q is proportional to corresponding temperature T. Therefore, efficiency η of ideal Carnot engine is provided by

η = 1 - TL/TH

It means that efficiency of the heat engine can be increased by reducing value of TL. Therefore, for greater efficiency, large quantity of water should flow as coolant through power plant to keep temperature TL as low as possible. Of course, this water has to come from environment. Water is eventually recycled back to where it came from. As more and more heat is transferred to water, its temperature continues to rise. Resulting warm water holds less oxygen. Consequently, this procedure can cause important damage to aquatic life in environment.

At times, large cooling towers are utilized to exhaust heat at electric- generating plant. Cooling towers discharge heat in atmosphere. Heated air resulting from this procedure can negatively affect weather of the region. Therefore, this method gives rise to severe environmental pollution.

Fossil-Fuel Steam Plants:

Fossil-fuel steam plant burns coal, oil or natural gas to boil water and generate high pressure steam which turns turbine. Such steam plants are very helpful to man. Though, they also generate severe environmental problems. Product of their combustion produces air pollution; heat condemned at the lower temperature reservoir produces thermal pollution; extraction of the minerals produces environmental disasters and oil spills create environmental nightmares. Such problems have capacity to wipe out every possible means of livelihood in affected places.

Nuclear Energy:

Nuclear energy may be released by procedure of nuclear fusion or by the process of nuclear fission. Nuclear fusion engages coming together of two or more light nuclei (such as hydrogen nuclei) to form more massive nucleus. Nuclear fission engages splitting of massive nucleus (such as uranium or plutonium nucleus) to create smaller nuclei. In both situations, vast amounts of nuclear energy are released. Nuclear fusion procedure has two major difficulties. First is the complexity faced in producing extremely high temperatures required to start thermonuclear reaction. Second is the problem of containment. Therefore, all the present-day nuclear power plants utilize fission procedure to produce energy. Nuclear power plant may, thus, be regarded as steam engine which uses uranium as its fuel. Under normal circumstances, nuclear power plant generates practically no air pollution. It doesn't release any carbon-dioxide (CO2) in environment. Therefore, neither fusion procedure nor fission procedure contributes to greenhouse effect. Though, nuclear accidents can deal devastating blow to environment.

Geothermal Energy:

In some places, underground water makes contact with hot interior part of the earth. Due to this the temperature of water rises considerably. When this occurs, hot water may come to surface as hot springs or steam vents. Such natural vents can be utilized to generate steam required to drive turbine. At times, scientists and engineers drill holes from surface of earth to the steam beds trapped below ground. Cold water may also be heated by causing it to make contact with hot dry rock. Geothermal energy is largely clean. It creates practically no air pollution. Though, any non-steam emission from a geothermal plant may still be destructive to environment. But, more serious problem is thermal pollution resulting from spent water. Mineral content of the spent water may be unfriendly to environment. Especially, these minerals may be corrosive.

Hydroelectric Power Plant:

In hydroelectric power stations, falling water is utilized to turn turbines of electric generators directly. Due to this, hydroelectric power plants don't require heat engines. Generally, turbines are situated at base of a dam. Hydroelectric power plants are approximately 100% efficient. Though, reservoirs behind dams inundate lands which may otherwise be utilized for agricultural and other purposes. Thus, environment also suffers.

Tidal Power Plants:

Unfavorable effect of tidal power on environment is negligible. Yet, abrupt changes in water level, as tidal power plant works between high-tide and low-tide sessions, can have a harmful effect on wildlife.

Wind Power Plants:

Wind mills of different shapes and sizes may be utilized to turn turbines to produce electrical energy. In general, windmills are considered as clean source of energy. Though, a large array is needed to meet important portion of country's energy requirements. Such large arrays might affect weather and damage beauty of affected place.

Solar Energy:

Solar energy can be harnessed by active solar heating, passive solar heating and photovoltaic cells. Similar to heat engines, efficiency of this cells lies somewhere between 30% and 40%. Solar energy is very helpful to man. For example, photovoltaic cells might be placed at rooftops for home use. Solar energy is, to a large extent, considered clean. Though, chemical pollution resulting from large scale manufacture of solar cells impacts unfavorably on environment.

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