My Science School

The word ‘detergent’ means any substance that cleans things. But today the word is usually used to mean synthetic or man-made detergents such as washing powders.

A detergent is an organic substance composed of carbon, oxygen, sulphur and hydrogen compounds. When combined with water it helps to clean soiled materials. The ordinary soap is a type of detergent, but it has a different chemical composition. The household detergents, used mainly for cleaning clothes and utensils, come in powder, flake or liquid form.

The first detergent was developed in 1916 by a German scientist called Fritz Gunther. Since then their use has been on the constant increase.

All the detergents contain a basic cleaning agent called a surfactant or surface-active agent. The surfactant molecules attach themselves to dirt particles in soiled materials like cloth etc. They pry the dirt particles from the cloth and surround the particles with a layer of water that allows them to be carried away. The surfactants that are made by treating beef fat or tallow with various chemicals increase the wetting ability of water by lowering its surface tension. The surface tension is the force that keeps water molecules separate and help to move deeper into soiled materials. This helps remove deep-seated dirt particles in fabrics. For example, surfactants also help detergents create lather and suds. Contrary to the popular belief, lather and suds have very little to do with the cleaning ability of a detergent.

Most of the detergents contain many other agents besides surfactants, including bleaches, fabric brighteners, builders and stabilizers. They also contain anti-redeposition agents that prevent removed dirt particles from returning to the cleaned material.

The surfactants can be divided into three main groups: anionic, which become negatively charged ions when in solution; cationic - which form positive ions in solution; and non-ionic which do not become ionized. Detergents may be anionic, cationic or non-ionic or mixture of two or more type of surfactant.

 

Continue reading "How do detergents perform the cleaning action? "

 

 

          The ammeter is an instrument used for measuring electric current. The current is measured in amperes. There are three main kinds of ammeters: (i) moving coil ammeter (ii) moving iron ammeter and (iii) a hot-wire ammeter.

          The moving coil ammeter is like a galvanometer. It has a strip of soft iron which causes to move in the magnetic field created by the current flowing coil. 

 

 

 

 

 

          The moving-iron ammeter has two pieces of iron inside a coil. One of the iron pieces can move. The other piece cannot move. The current passing through the coil produces a magnetic field. The force of the field moves one piece of iron away from the other. A needle attached to the moving piece on a scale indicates the current. These ammeters can measure both direct and alternating current. 

Continue reading "What is an ammeter? "

                The ballistics is a branch of mechanics which deals with the motion behaviour and characteristics of projectiles, such as bullets, bombs, rockets and guided missiles. There are three main branches of ballistics, namely; interior ballistics, exterior ballistics and terminal ballistics. The ballistic missile is a ground to ground missile with a parabolic flight path which is propelled and guided only during the initial phase.

                The interior ballistics deal with the motion of a projectile as it travels down the barrel of a weapon, such as a rifle or pistol. The weight of the bullet, the pressure placed on the bullet, the speed at which the bullet moves through the barrel, the barrel’s length and diameter, and the speed at which the bullet leaves the barrel-all affect the flight of the bullet. The interior ballistics of missiles is concerned with the design of rocket engines and the choice of propellants. 

Continue reading "What is the science of ballistics? "

               A welding torch is a mechanical device that produces a hot flame by mixing gases for the welding or cutting of metals. This device is used to join metal surfaces by raising the temperature high enough so as to melt the joining ends and then fuse them with or without a filter metal. After the heat is removed the joint solidifies and fuse permanently. This torch usually produces a flame temperature of 2750°C to 3300°C by mixing acetylene and pure commercial oxygen which is sufficient to melt the metal locally. The torch thoroughly mixes the two gases and has facilities to adjust and regulate the flame. 

               Welding torches are of two types: low pressure torch and high pressure torch. On a low pressure or injector torch, acetylene enters a mixing chamber where it meets a jet of high pressure oxygen. The amount of acetylene drawn into flame is controlled by the velocity of this oxygen jet. In a high pressure torch both the gases are delivered under pressure. The heat generated at the work is controlled principally by the size of the nozzle or the tip fitted onto the torch. The larger the tip, the greater the gas pressure. Small flames are used with thin-gauge metals. Larger flames are necessary for thick metal parts.

               A welding torch mixes the fuel and gas internally and well ahead of the flame. For cutting, the torch delivers an additional jet of pure oxygen to the centre of the flame. The oxyacetylene flame produced by mixed gases raises the metal to its ignition temperature. The central oxygen jet oxidizes the metal, the oxide being blown away by the velocity of the gas jet to leave a narrow slit or kerf. The temperature for the cutting action, once initiated, is maintained by the oxidation of the metal. Nowadays automatic torches have been developed for precision, cutting and welding.   

            Hardness is a characteristic property of the solid objects. It is measured by the resistance which the body offers to anything which tends to scratch it. The hardness of the various materials is measured either on the ‘Mohs’ scale or the ‘Knoop’ scale.

            The Mohs’ scale, first devised in 1822 by Friedrich Mohs, measures resistance to indentation as judged by the material that will scratch another. Mohs’ scale is numbered from 1 to 10, that is, it gives ten grades of hardness. In this scale diamond is the hardest material and talc is the softest. Diamond has a hardness of 10 Mohs and talc has a hardness of 1 Mohs.

            Mohs’ scale, which assigns numbers to natural minerals, has been widely accepted and is used by mineralogists. This test, however, is not quantitative. For example, the hardness of sapphire is 9 on the Mohs’ scale; it does not mean that sapphire is 10% softer than diamond.

            The mineralogists carry a box containing pieces of the above minerals for testing samples in the field. For example, if they find a mineral that can be scratched by feldspar but not by appetite, its hardness lies between 5 and 6 on the hardness scale.

            To measure hardness in the Knoop scale, an elongated diamond-shaped indenting device is employed to measure the indentation it makes in a given test material. By this method, the hardness of extremely brittle materials including glass and even diamond can be measured without damaging either the indenter or the test piece. The size of the indentation is taken as a measure of the material’s hardness.

 

          An abrasive is a substance used for grinding, cutting, scroping or polishing the materials. There are two types of abrasives: natural and artificial abrasives. Natural abrasives include quartz, sandstone, pumice, diamond and corundum; artificial abrasives include rouge, whiting and carborundum.

          Abrasives are available mainly in two forms: paper and grinding wheels. The abrasive paper is made by coating ordinary paper with glue and adding the abrasive material to it. The sandpaper, emery paper, and carborundum paper are made in this way. To make a grinding wheel, abrasive material such as quartz is mixed with clay and water. This mixture is then pressed into the desired size and shape and fired in a furnace. The heat inside the furnance makes a strong bond among the materials put inside the furnance. 

          The fineness or coarseness of the particles used in an abrasive material is described in terms of its ‘grit number’. The abrasive materials with a grit number of 60 are much finer than those with a grit number of 30.

The hardness of an abrasive is also an important factor. It is measured on the Mohs’ scale. The Mohs’ scale ranges from 1 to 10. An abrasive is chosen according to the material to be ground. It should be harder than the material that is to be polished.

          The most widely used abrasives are fused aluminium oxide and silicon carbide. The aluminium oxide is known as alumina. It is used to grind and polish metals like steel, wrought iron and hard bronze. The silicon carbide is known as carborundum. It is made by fusing sand and coke in an electric furnace. Carborundum is used to grind and polish brass, copper, aluminium, stone, glass and ceramics.

          Many varieties of quartz are also important abrasives. Pumice, a volcanic rock, when ground to a fine powder, can be used in scouring powder and soaps. Crystalline iron oxide is used to polish jewellery and glass. It is known as rouge because of its red colour.

          The synthetic diamonds, diamond powders and diamond pastes are also used as abrasives. They are used to make drill bits and cutting wheels. Tungsten carbide is used in the machine tool industry for drilling, cutting and polishing metals. Boron carbide is another important abrasive. It is valuable because it is almost as hard as diamond. It is also used in nuclear reactor as a moderator and also as an abrasive. 

 

            A clinometer is an instrument used by surveyors and civil engineers to measure the angle of inclination of slopes and hills by referring to a plumb bob or spirit level. It is also used to measure the height of an object if the distance from the observer to the object is known. A clinometer is also called Abney level.

            It consists of a sighting tube surmounted on a graduated vertical arc with an attached spirit level. A 45° mirror inside the tube enables the observer to see the bubbles at the same time the observer sights a point or a graduated rod with a horizontal wire. The surveyor first makes sure that the bubble is in the middle of the spirit level tube. This indicates that the clinometer is being held in a horizontal position. He or she looks through the eye hole and adjust the vertical arc to coincide with the sighted point. The vertical angle is indicated on the arc.

            In the ‘plumb-bob’ clinometer, a plumb bob or a weight attached to a piece of string hangs from the sighting device. As the device is tilted upward to view the top of the hill, the string moves across a protractor like face and indicates the angle of inclination.

            The clinometer is mainly used to measure the angles of slope. If set on a slope it can be used to give the angle of inclination of the surface. With the arc set at 0°, it can be used at a hand level.

 

               Electroplating is a process of metal coating through electrolysis. Electrolysis is passing of an electric current through an electrolyte solution. In other words, it is the process to cover a metal with a thin coating of another metal either for protection against corrosion or for beautification of house hold items. The electroplating may also be used to impart certain other properties to a metal surface, such as hardness, wear resistance and anti-frictional, electrical, magnetic or optional properties. Do you know how metals are electroplated?

               Electroplating is done in large vats containing a solution of some suitable salt of the metal to be coated. Bars or plates of metal are used as anode, and are arranged inside the vats. This metal body, called the work piece, makes the cathode. When the electric current is passed through the solution, by connecting the positive terminal of the battery to the anode and negative terminal to the cathode, the metal ions from the solution go towards the cathode and get deposited on the work piece and form a thin layer of metal on it. The metal from the anode goes on dissolving in the solution and finally gets deposited on the work piece.

               To ensure an even deposit, the work piece may be slowly rotated inside the vat. The surface to the work piece must be clean and free from grease, dirt or oxide films. These days the metals that are electroplated include silver, gold, nickel, copper and chromium. For silver plating, double cyanides of potassium and silver are used. The silver plating is usually done on brass table-wares such as spoons, forks and other utensils. It is also done on ornaments. The gold baths also contain double cyanides of gold and potassium. This plating is also done on ornaments. The nickel plating baths involve double sulphates of nickel and ammonium. The copper bath contains a solution of copper sulphate with small quantities of sulphuric acid. The chromium plating is done by using the solutions of chromic acid and chromic sulphate with small quantities of chromium carbonate usually used on machine parts.

               The other metals which are electroplated commercially include cadmium, cobalt, platinum, rhodium, tin, zinc, etc. In certain cases two or more metals are plated simultaneously as alloy coatings, e.g. copper-zinc, copper-tin, lead-tin, lead-tin-copper, tin-nickel and nickel-cobalt.

            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. 

          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.

 

            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. 

Continue reading "What is light? "

          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. 

               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.

 

            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. 

Continue reading "How does a turbine work? "

            A battery torch is a portable electrical appliance used for lighting. It has a variety of uses. Doctors use it to examine closely the ears, eyes, noses and mouths of the patients. Do you know how a torch produces light?

            A battery torch can be divided into four main parts: the battery, bulb, case and the switch. The battery is in the form of dry cells. Dry battery cells such as those in torches, transistors or calculators produce electricity only for a limited time. Most of the torches make use of two or three dry cells. The body of the torch is fitted with a bulb and dry cells. When the switch of the torch is pressed, the cells get connected to the bulb, and as a result of this the bulb emits light.

            The torch produces light by connecting the positive and negative terminals of the dry cells to the bulb. The current passes out at the positive contact through the bulb and returns back via the negative contact, thus making a complete circuit.

            When the switch is moved to the ‘on’ position, a metal piece inside the case touches the positive terminal of the battery, letting the electricity flow out to the bulb. In some other torches, the battery is pushed up so that the positive contact touches the bulb itself. In a battery torch, there is a reflector which reflects back the light to long distances.