Category Science

How do satellites stay up in space?

            A satellite is a body that moves in orbit around a larger body. The moon is a natural satellite of Earth because it orbits around the Earth. All the planets, except Mercury and Venus, have natural satellites.

            Today we also have artificial satellites. These ‘artificial’ satellites are man-made and launched into the space by powerful rockets. They orbit around Earth performing certain specified tasks.

            A satellite orbiting the Earth is like a chest-nut being whirled on the end of a piece of string. The centrifugal force drives it outwards, but Earth’s gravity keeps it from moving away. These two forces balance it and the satellite continues to orbit around the earth. It moves without any resistance since there is no air in the space. It will keep on orbiting forever, unless the upper atmosphere of Earth drags on the satellite and slows it down. The satellites move in elliptical orbits and not in circles. The nearest point to Earth is called the perigee and the farthest, the apogee. Manned space craft’s are temporary satellites during a space mission, but most artificial satellites are unmanned. The geostationary satellites positioned at a height of about 36,000 km. have the advantage that they have a stable position in the space in respect to any point on Earth.

            Hundreds of artificial satellites have been launched since Sputnik I which was the first satellite to be launched by the Soviet Union on October 4, 1957. Artificial satellites have become an integral part of our day to day life. They serve many useful purposes in different fields — communication, weather forecasting, geological survey, oceanography, astronomical experiments and observations etc. They also help in navigation and air traffic control. The satellites can be either unipurpose or multipurpose, depending on their service in either one specific area or more than one area. The Indian National Satellite (INSAT) series is a multipurpose one used for domestic telecommunications, meteorological observations, radio and TV broadcasting etc. 

How is sulphuric acid manufactured?

          Sulphuric acid is called the king of acids because of its importance as an industrial chemical. It is used in the manufacture of fertilizers, dyes, drugs, explosives, paints, synthetic fibres and detergents. It is also used in the manufacture of other acids such as hydrochloric acid and nitric acid. Different metals are pickled in sulphuric acid to clean them. It is also used in refining sugar and petroleum and to produce a vast range of chemicals. Do you know how this acid is manufactured?

          There are two methods used to manufacture sulphuric acid. One is known as Lead Chamber Process which dates back to about 200 years. The other is known as Contact Process. The former is less efficient and complex than the latter; still it is of considerable commercial importance. In Lead Chamber Process, first sulphur dioxide is obtained by burning sulphur or roasting pyrites. Then the sulphur dioxide thus obtained is oxidized by oxides of nitrogen to get sulphur trioxide which reacts with steam to produce sulphuric acid.

          Sulphuric acid is commercially manufactured by contact process. In this method the sulphur dioxide gas is mixed with air and heated with a catalyst. The catalyst is either the metal platinum or a compound called vanadium pentaoxide. The catalyst helps to quicken the reaction. The sulphur dioxide combines with the oxygen in the air to form sulphur trioxide. When sulphur trioxide is dissolved in water, it forms sulphuric acid.

          Pure sulphuric acid is a heavy, oily, colourless liquid. It is very reactive and attacks most of the metals to form salts called sulphates. It quickly absorbs water and is often used as a drying agent.

          While handling sulphuric acid, one should add sulphuric acid to water and not vice versa. If water is added to sulphuric acid, the heat produced causes water to boil. This makes the hot acid spit dangerously.

 

What is light?

            For thousands of years many scientists groped in dark to understand the true nature of light. The ancient Greeks believed that light consisted of rays of matter given out by whatever object was being looked at. Plato and his followers believed that it was a mixture of different matters coming from the sun. But in the 11th century it was Alhazen, the Arabic scientist who was the first to propound the theory that light could be given out by all luminous object.

            In the 17th century, the British scientist Sir Isaac Newton put forward the corpuscular theory of light. According to this theory light travels in the form of corpuscles in straight lines through imaginary medium called ether. This theory could not explain some of the observed phenomena such as interference and diffraction. In an attempt to explain these phenomena, Christian Huggens of Holland proposed the wave theory of light. He maintained that light consists vibrations at right angles to the direction of propagation. It travelled in the form of waves which spread in straight lines. He continued that the medium in which light travels was ether which was believed to be an invisible and omnipresent substance. This classical wave theory existed for hundred years. Although it explained the phenomenon of reflection, refraction, interference and diffraction of light, it could not explain the transverse nature of light. 

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How does a siren produce sound?

          A siren is a device basically used to make a warning or to give a signal. It produces a loud, piercing sound of a definite pitch. It is powered by electric motors, steam or hand cranks.

          Sirens are used for various purposes, for example, in factories warning signal for any danger or accident; for cautioning people in case of enemy attacks; for traffic clearance by the vehicles of emergency services etc.

          Siren was invented in the late 18th century by a Scottish natural philosopher, John Robinson. It was named thus by a French engineer, Charles Cognaird de La Tour, who devised an acoustical instrument of the type in 1819 which is not generally used nowadays.

          The Cognaird siren consists of a cylindrical hollow box ‘C’, known as the wind chest. It has a fixed top lid ‘B’ that consists of a number of equidistant slanting holes arranged in circles. The chest is fixed at its lower end with a tube ‘T’, through which air can be blown in it by means of bellows. Another disc ‘D’ of the same size, with equal number of equidistant holes slanting in the opposite direction covers the first disc. This disc can be rotated by a mechanical arrangement. The air under pressure is forced into the wind chest of the siren due to which the disc begins to rotate. The air passes through the holes in the lower disc, and comes out through the holes in the upper disc. Every time the holes in the upper disc are above the holes in the lower disc, a puff of air escapes. This creates a sound. The pitch of the sound depends upon the speed at which the disc rotates.

          Now improved versions of this siren are available. One of such types of siren uses two small cylinders one inside the other, which have holes in them. An electric motor rotates the outer cylinder. Another device forces air or steam through the cylinders. The holes in the cylinders are actually small slots which are cut on a slant in lines encircling the cylinders. The air enters the slots in the first cylinder, and then passes through the slots in the second cylinder. Every time the slots are exactly opposite to one another, a sound is created by this movement of air through the slots. The faster the rotation of the outer cylinder, the louder the sound. 

How are metals anodized?

               Anodizing is a process of coating a metal with a protective oxide layer on the surface to resist the corrosion of the metal. This can be done by either chemical or electrolytic means. In this regard, mainly aluminium or magnesium is anodized. However, metals like beryllium, tantalum, titanium and zinc can also be anodized. 

               The natural oxide film on aluminium is thin. Anodizing makes a thicker oxide layer. This protects the aluminium from corrosion and makes it last longer.

               In anodizing, aluminium is used as the positively charged electrode of an electrolytic cell. Electrolytes such as sulphuric acid or chromic acid are used as a solution. The oxide layer forms from the metal surface outside. This makes the outside layer slightly rough and porous. After anodizing, the pores on the metal are sealed by hot water or steam treatment which causes dehydration and results in the expansion of volume of the oxide. This further prevents corrosive substances from attacking the metal.

               Anodizing with sulphuric acid makes a clear oxide film. With chromic acid, a dull film is produced. Even coloured films can be produced by using dyes. Chromic acid is also used for anodizing zinc.

 

How does a turbine work?

            A turbine is a machine used to convert energy generated by a moving liquid, gas or air into work. For example, the energy produced by fast flowing water is made to spin a rotating shaft by pushing on the angled blades set around a wheel mounted on the shaft, and this action produces the required work. The generated work helps to drive machines like propeller of a ship or an aeroplane or electric generators to produce electricity. The gas or liquid used in a turbine is known as the working medium. The working medium can be water, steam, gas or air.

            The water turbines use water from a waterfall or a dam to drive the turbine. There are two different methods to make the turbine wheels rotate. A water jet may be directed onto the blades. This is called a reaction turbine. In the second method, the turbine wheels are submerged in the flowing water. These turbines are used at hydro electric power stations. 

            For a steam turbine to operate, first the steam must to be produced by heating water in boilers. The steam enters the turbine at a high pressure. Inside the turbine, the pressure drops and the steam expands. This expansion drives the wheels around. Steam turbines have a series of wheels, mounted on the same shaft. This is because the steam expands gradually as it moves through the turbine. 

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