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Old Tuesday, August 23, 2005
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a) Communication Satellite :communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use geosynchronous orbits, Molniya orbits or low Earth orbits.

For fixed services, communications satellites provide a technology complementary to that of fiber optic submarine communication cables. For mobile applications, such as communications to ships and planes, for which application of other technologies, such as cable, are impractical or impossible.

b.Geothermal means "Heat from the Earth". The heat that flows from the Earth's hot interior due to crustal plate movements, zones of high heat flow may be located close to the surface where convective circulation plays a signifcant role in bringing the heat close to the surface. Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma.

Almost everywhere, the shallow ground or upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger—a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.
Ultrasonics, branch of physics dealing with high-frequency sound waves, usually in the range above 20,000 hertz (Hz), that is, above the audible range. It is to be distinguished from supersonics (see Aerodynamics), which deals with phenomena arising when the velocity of a solid body exceeds the speed of sound. Modern ultrasonic generators can produce frequencies of several gigahertz (1 GHz = 1 billion Hz) by transforming alternating electric currents into mechanical oscillations. Detecting and measuring ultrasonic waves are accomplished mainly through the use of a piezoelectric receiver (See Piezoelectric Effect) or by optical means, because ultrasonic waves can be rendered visible by the diffraction of light.
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