My Science School

The term laser stands for “light amplification by stimulated emission of radiation”. A laser produces a very thin but very powerful beam of light, so powerful that it can drill a hole through the hardest substance – diamond. Unlike the light from a torch or a fluorescent tube, a laser beam does not spread much. Laser light contains light of only one colour, unlike sunlight which is a mixture of seven colours. Laser beams are highly monochromatic and coherent. The density of their energy also remains the same even over long distances. If comparisons can be made, ordinary light is like a crowd while the laser light is a well ordered army platoon.

The first laser was made in 1960 by an American scientist named Theodore H. Maiman. It was a ruby laser which produced a red beam of light, million times brighter than the sunlight. Today we have different types of lasers which produce different wave-lengths of different powers. Some of the well-known lasers are Ruby, Nel, Yah, He-Ne, Argon, Diode laser etc. A laser has three main parts. They are (1) the medium – the material that produces the beam (such as a ruby crystal or a gas); (2) the power source that energizes the medium and; (3) the resonator to make the beam more powerful (usually mirrors that reflect the light backwards and forwards to build up its strength).

Lasers are used by doctors to perform delicate surgeries, such as re-attaching a detached retina of the eye. The laser treatment is painless and the patient remains conscious during the operation. Laser beams are being used in the treatment of cancer and to stop tooth decay. A laser can be used by a surveyor as an infinitely tall ‘ranging pole’, from which to take bearings and measurements. The laser beam is fired vertically into the sky, and it provides an easily detected fixed point for other surveyors, even if hills and forests are in the way. Builders of skyscrapers use laser beams like plumb-lines to check that the building is vertical. Unlike an ordinary plumb-line, a laser beam cannot be blown by the wind. Because the laser beam is so straight and narrow that it makes an excellent measuring instrument for astronomers. The Apollo astronauts who landed on the Moon in 1969 left behind a laser reflector. Laser pulses were sending from the Earth to hit the reflector, and the beam bounced between the Earth and the Moon accurate to within 15 cms.

Laser beams are used by soldiers as range-finders, target designators, and guided missiles. Experiments are being conducted with lasers as space weapons, for destroying satellites and ballistic missiles.

Lasers are also being used in several fields of research such as Roman effect and interferometry. Lasers are being used in communications, computers, welding and drilling of metals, photography, stone removal from kidneys without operation, heart surgery, meteoreology etc. 

          John A. Larson, a medical student from California University developed a machine in 1921 which can detect lies with a fair degree of accuracy. This machine is known as ‘polygraph’ or a lie detector. In 1972, the American inventor Allan Bell developed another improved model of a lie dictator which was able to detect slight trembling in the voice which often occurs when a person tells a lie. Today, it is widely used in crime detection. How does this machine detect lies?

          When someone tells a lie, there occur certain physiological changes in his body. His heart begins to beat faster leading to rapid perspiration. His blood pressure and breathing pattern change. His voice also starts trembling. This machine is designed to record all these changes.

          When a person undergoes a lie-detector test, various parts of the machine are attached to his body by wires. The interrogator asks the person all relevant questions. The physiological changes taking place while questioning are recorded by a pen recorder fitted in the instrument. Finally, these observations are analyzed.

          However, the polygraph is not wholly dependable. Its accuracy is estimated to be about 80%. In fact, a lot depends on the skill of the examiner in this regard. Some people, who are truly unaware of the fact that they are lying, cannot be caught by the lie-detector. Moreover, the hardened criminals can control their emotions and render this machine ineffective. Because of these reasons the results of a lie-detector test cannot be accepted as evidence in the court of law. However, it is being used by the police departments in almost all the countries.

 

Holograms are amazing pictures that appear to have depth just like the real object. For example, if you look at a hologram of the front of a cube and then move to one side, you will see the sides of the cube just as if you were walking around it. Holograms are made with lasers.

An ordinary photograph records the variations in light intensity reflected from an object. Holography, however, records not only the intensity of light but also its phase. In an ordinary photograph, we get two dimensional images but in holography we get three dimensional images.

Holography is the means of making three dimensional pictures called holograms. It was invented by Dennis Gabon, a Hungarian born physicist who worked in Britain in the year 1948. He was awarded Nobel Prize for Physics in 1971. But the actual holography became possible only after laser was developed at the beginning of the 1960. The intense-coherent light of laser allowed high quality holograms to be made.

To make a hologram, the object is lit by light from a laser. This light reflects from the object and strikes a photographic plate placed nearby. At the same time, the laser beam is split so that it also reflects from mirrors and strikes the plate directly.

The plate is then developed. A black and white pattern appears on it, producing a holographic plate. When one side of this plate is lit up by a laser beam and it is viewed from the other side, an image of the object appears behind the plate. The image is in three dimensions just like the real object, but in the colour of the laser light. Projection holograms can be projected by lasers to appear in front of the holographic plate. There are also special holograms that can be seen by day light.

Holograms have proved very useful. They are used to record very small changes in the size of the objects. This is because they can record an object from many angles with a great accuracy. Scientists use them to study the growth of crystals or the build-up of dirt on old oil paintings. They can be used in computer memory systems to store information. In the field of industries holography is being used to prevent the pirating of the goods of big companies. In India also, some big companies are using the holograms to distinguish their original goods from the copied ones. 

          Man has been using artificial lights ever since he discovered fire. In the beginning, it used to be just the log fire, and then the wick on the edge of a stone bowl filled with animal’s fats and then the candles. A great step in this field was made by Thomas Alva Edison who invented the modern electric bulb in 1878. And by 1930, the scientists of America and Europe had developed the wonderful fluorescent tube.

          A fluorescent tube light consists of a long glass tube coated with a fluorescent material. Two tungsten electrodes are fitted at the end of this tube. The tube is evacuated and filled with a little amount of mercury and argon gas. When the tube is connected with the electric line, tungsten electrodes get heated up and start producing electrons. These electrons collide with mercury atoms and produce ultraviolet and visible light. Ultraviolet light, on colliding with fluorescent material, is turned into visible light. The colour of this light depends upon the fluorescent material.

         These tubes are coated with calcium tungstate to produce blue light. A coating of calcium silicate produces pink colour while that of zinc silicate produces green light.

         A fluorescent light is definitely an improvement on the ordinary bulb. Its electric consumption is very low but the light-producing efficiency is better than the bulb.

 

          A planetarium is a special type of building where a dumbbell shaped planetarium projector is used to recreate the night sky on the inside of the dome-shaped ceiling. It is a very complex instrument fitted with lenses, prisms and mirrors. It can not only show the stars almost exactly as they appear in the real sky, but can also show their movements from season to season or as they appear from different places. It can also duplicate the movements of the Sun, Moon, planets and other heavenly bodies in the sky. Modern planetariums are also equipped with slide projectors that can simulate events like space travel and landing on other planets. The planetarium is used to educate not only astronomers and navigators but also students about the Universe. It also provides spell bounding spectacle to a lay person.

         The first planetarium was built by Walter Bauersfeld of the Zeiss Optical Company of Jena (Germany) in 1923. The apparatus was kept at the centre of the dome. It could reproduce the real sky. The motions of the heavenly bodies taking place in one year could be reduced to an interval varying from several seconds to half an hour.

         Planetariums are useful because it is very difficult to learn about heavenly bodies just by looking at the sky since it is a very time consuming process to track the heavenly bodies due to pollution, clouds, etc. In a planetarium the motions of heavenly bodies taking place in a year can be watched in an interval of a few seconds.

          Today all big cities of the world have these dome-shaped buildings equipped with planetarium projectors to educate people. The biggest planetarium is in Moscow. It is located in a building with a diameter of 25.15 meters. The planetarium in San Francisco, USA, contains about 25,000 mechanical parts and weighs 2.5 metric tons. In our country there are planetariums in cities like Bombay, Calcutta, Jaipur, Delhi and Bangalore and thousands of people visit them everyday. 

           Cosmic rays are streams of high-energy charged tiny particles that constantly enter the atmosphere of the Earth from outer space. They consist mainly of 89% protons, 9% radiations and 2% of heavy nuclei of carbon, nitrogen, oxygen and iron. These are called primary cosmic rays. They travel nearly at the speed of light.

          When these tiny particles of primary cosmic rays collide with the nuclei of the air, they produce new particles called secondary cosmic rays. Secondary cosmic ray particles also travel at high speeds. They further collide with other atoms and again create new particles. After several collisions on the way, only very few secondary cosmic ray particles are able to reach the surface of the Earth. Secondary cosmic rays consist mainly of positrons; neutrons, mesons and neutrinos. All these particles are called elementary or fundamental particles.

          Where do these cosmic rays originate in space? It is believed that most of the cosmic rays originate in the supernova explosions far beyond our Milky Way and some of them are produced by storms on the Sun and stars of the galaxy. More and more information is being gathered about the origin of these rays.

          The small amount of radiation caused by cosmic rays is not enough to harm the Earth. They can do little damage to the human body. These rays have been colliding with the Earth for billions of years and life has been least affected by them. So, it is believed that cosmic rays are harmless. However, there is a possibility that cosmic rays may have a harmful effect on astronauts because the intensity of cosmic rays is far greater in space than on the Earth.

 

          There was a time when man used to communicate by beating drums or burning fires. Those days, in the absence of any scientific knowledge, it was extremely difficult to send messages to distant places. Today, we have different means of communication like the telephone, radio, television and the press. Now scientists have added artificial communication satellites or comsats to send telephone, radio, telex, fax messages and television signals around the world.

          An artificial satellite is a man-made Moon that orbits around the Earth. With the help of rockets, they are launched into geostationary orbits. This means that they are placed in fixed orbits over the equator about 36,000 km high where they orbit the Earth in exactly 24 hours. Because of this they appear to remain stationary in the sky from the Earth. Artificial satellites are of many different shapes and sizes and are sent into orbit for several different reasons. They usually have solar cells which convert the energy of the Sun into electricity which is used to run the satellite instruments. 

          Communication satellites pick up the signals transmitted from a point on the Earth and relay them to the other side of the world by amplifying them and then beaming them down to a ground station. Communication satellites have different channels for telephone, radio and television signals. The signal is first sent to the satellite with the help of high-frequency microwaves. This is received by the antenna fitted in the satellite. After amplifying, it is transmitted by a transmitter. Its power is increased by a transponder. The signal is received by the earth station. This is how a signal travels thousands of kilometres. If a message is sent through conventional methods, very long cables are required. Today, telephone messages between several countries are exchanged through satellites.

 

Continue reading "What are communication satellites? "

          Cement, today, is by far the most useful of all the building materials. It is being used in all countries throughout the world as a binding material in the construction of buildings and civil engineering. It is a grey coloured powder. When mixed with water and allowed to settle for some time, it becomes as hard as stone. The principal minerals in cement are lime (which comes mainly from limestone), silica and alumina (which are provided by clay). Cement was discovered by the Romans around 250 B.C. They made it by mixing slaked lime and sand with volcanic ash. As it was obtained from a place named Pozzuoli, it was called pozzolana. Upto the middle of the 18th century, it was in common use. In 1757 an improved version was developed by John Smeaton, a British engineer. It was obtained by heating a mixture of slaked lime and clay. It remained in use for many years.      

          The most common kind of cement was made by an Englishman, Joseph Aspdin in 1824. When set, its colour would become similar to that of Portland stones. Hence, it was called Portland cement. Portland cement is made by mixing one part of clay and three parts of limestone in a very hot oven. Both the raw materials are powdered with the help of a crushing machine and mixed together by a blending mill. This mixture is then sent to the hot oven called a kiln. It is heated to about 1500-1600° C to form a hard mass called clinker. When the clinker cools down, it is grounded into a fine powder with mineral called gypsum in a grinder. About 3% of gypsum is added to it to regulate the time that the cement takes to harden. This is known as the Portland cement.

          In India, the Indian Cement Company was established at Porbunder in 1914. Today, cement is being manufactured on a large scale to meet its increasing demand. As a result of its increasing demand, scientists have also been able to develop special cement from rice husk. 

For many centuries man had been dreaming of space travel and exploration of extra-terrestrial lands. The first concrete step in this direction was taken by the Russians when they launched the artificial satellite Sputnik I on 4 October, 1957. A month later on 3 November, 1957 a bigger Sputnik II was sent into the space. It took along, the first living creature, a dog named Liaka. Following closely on the heels of the Russians, the United States launched its first satellite Explorer I, on 31 January, 1958 triggering off a race between the two countries in space research. The first man in space was a Soviet cosmonaut, Yuri Gagarin, who orbited the earth on 12 April, 1961 in Vostok I.

In 1961, America started the famous Apollo project which was aimed at taking man to the Moon. It was an ambitious project with hurdles at every step. On 27 January, 1967 the Apollo project had a serious setback. During a practice session the astronauts Virgil Grissom, Edward White and Roger Chaffee were burnt to death in a fire aboard the spacecraft. This tragedy led to many modifications in the design of the spacecraft.

In July 1969, Neil Armstrong, Edwin Aldrin and Michael Collins went to the Moon in Apollo - 11. On 20 July, 1969 at 10.56 p.m. (GMT) Neil Armstrong put his first step on the surface of the Moon. He sent the message to the Earth, ‘That’s one small step for a man, one giant leap for mankind’. A little later, Aldrin also landed on the Moon. Michael Collins remained in the spacecraft. Armstrong and Aldrin stayed on the Moon for 21 hours and 35 minutes.

After this, four successful landings of the Apollo on the Moon followed. The final landing was on 11 December, 1972 by Apollo 17. Eugene Cernan and Harrison Schmitt spent 74 hours and 59 minutes on the moon and returned with 113.6 kg of lunar material. The first Indian to go to the space was Sq. Ldr. Rakesh Sharma in a joint Indo-Soviet flight on 3 April, 1984.

So far a total of 12 Americans walked on the Moon during the Apollo programme, bringing back 380 kg of rocks and soil. They have moved about 100 km of the lunar surface in a total time of 166 hours. 

          Pure ghee and vanaspati ghee are a part of our daily food. Pure ghee is expensive while vanaspati ghee is comparatively cheaper. Because of this, pure ghee is often adulterated with vanaspati ghee and common consumers are cheated. Do you know how you can test the purity of pure ghee?

          Vanaspati ghee is manufactured by the hydrogenation of vegetable oils. In the process of hydrogenation, nickel powder is used as a catalyst and hydrogen is passed. By this process, unsaturated vegetable oils get saturated and are converted in what we call as vanaspati ghee. To test the presence of vanaspati ghee in pure ghee, we carry out the chemical test for nickel particles which are always present in traces in vanaspati ghee.

          To detect the presence of vanaspati ghee in pure ghee, we make use of hydrochloric acid and 2% solution of furfural in alcohol. These chemicals are easily available in the market.

          About 5 ml. sample of ghee is heated in a test tube. When it melts, about 5 ml. of hydrochloric acid is added to it. The tube is then shaken well. Now 5 to 6 drops of furfural solution are added and the test tube is again shaken well for four to five minutes. Now, if a pink colour develops, the ghee being tested is not pure. It means it contains vanaspati ghee, i.e. nickel particles. If there is no change in the colour, the ghee is pure. This system of detection is widely used by the ghee traders.

 

All elements are made up of tiny invisible particles called atoms. According to the scientists, at the centre of an atom there is a core called the nucleus around which the electrons revolve in different orbits. The nucleus is made up of two types of particles called protons and neutrons. All atoms of a particular element have the same number of protons in the nucleus. However, the number of neutrons in the nucleus can vary without changing the chemical nature of the element.

The number of protons in an atom is called its atomic number while the total number of protons and neutrons is called its mass number or atomic weight. Chemical properties of a substance depend upon the electrons outside the nucleus while the physical properties on its mass number. Atoms of the same element having the same atomic number but different mass numbers are called its isotopes. For example, hydrogen has three isotopes – protium, deuterium and tritium. Protium has only one proton, deuterium or heavy hydrogen has one proton and one neutron while tritium has one proton and two neutrons. Tritium does not exist naturally. It is produced by artificial means.

All the isotopes of the same element have the same chemical properties but different physical properties. Almost all elements are mixtures of isotopes. Oxygen and chlorine have two isotopes each. 

Isotopes of some elements are radioactive in nature, i.e. they emit invisible radiations and decay into isotopes of other elements. Isotopes of an element are separated by an instrument called mass spectograph. Particle accelerators are used to prepare ‘radio isotopes’.

Radio isotopes are very useful. Cobalt-60 and Radium isotopes are used to burn out cancerous growths. Carbon-14 is used to determine the age of the dead plants and animals. This process is called radioactive dating. Isotopes of iodine are used for the treatment of goitre. Artificial radio-isotopes are used to study the chemical reactions. They are also used as tracers to study the movements of compounds in plants and animals. With the help of isotopes many diseases are diagnosed. This branch of medicine is called nuclear medicine.

Manufacturers of precision instruments use some isotopes to detect tiny flaws in metal castings and to make extremely fine measurements.

 

          An alloy is an intimate mixture of two or more substances, at least one of which is a metal. The mixture is usually more useful than each ingredient on its own. Almost all alloys are made by mixing constituent elements in the required proportions in the molten state. Man has known a few alloys like brass and bronze since ancient times. Brass is an alloy of copper and zinc while bronze is an alloy of copper and tin.

          Most metals in their pure form are often too soft to be used for practical purposes. Their strength, ductility, hardness, melting point and colour can be improved by mixing one or more metals. For example, pure aluminium is light and weak but when copper and magnesium are added to it, its alloy becomes stronger. Copper and tin are soft and weak but when mixed together they become harder. Brass, a mixture of copper and zinc, is another strong and useful alloy. Mixture of lead and tin is used for soldering purposes. Alloys have more corrosion resistance and better casting properties than metals. 

          Today, the most important alloys are the alloys of steel. They are used for making different machine parts. Copper-nickel, bronze and aluminium alloys are used in minting coins, shipping and airplane industries. Lead alloys are used in the making of electrodes of storage batteries. Zinc alloys are used in the making of automobiles. Nickel-silver, an alloy of copper, nickel and zinc, is best known for its use in domestic cutlery. Expensive alloys of platinum, gold and silver are used in jewelry. Stainless steel, aluminium alloys, Nimonic alloys are 20th century alloys. Super alloys of tungsten and molybdenum are the development of recent years which have proved very useful in rocketry. Thus we see that alloys are very useful to us.

 

          Sulfa drugs are synthetic chemicals that are used to treat many diseases caused by bacteria. The first sulfa drug was developed by a German bacteriologist, Gerhard Domagk, in 1930. He showed through experiments that a sulfa drug called Prontosil could kill streptococcus bacteria. Sulfanilamide was the active chemical in Prontosil which killed the bacteria. Since that time, scientists have experimented with thousands of similar chemicals, but only about 20 of these are being used as medicines. 

          How do sulfa drugs control the bacterial diseases? Sulfa drugs operate by interfering with the normal metabolism of the bacteria cells. All living cells need folic acid to grow and reproduce. Human beings and many other animals get folic acid from their food. Bacteria, however, make their own folic acid. For this most bacteria need a chemical called para-amino benzoic acid (PABA). Chemically sulfa drugs and PABA are almost the same. The only difference between the two is that the sulfa drugs have sulphur atoms whereas PABA has carbon atoms. Bacteria cannot make out the difference between the two and absorb sulfa drug. This prevents the production of folic acid. Without folic acid bacteria cannot grow and reproduce. Thus, the sulfa drugs do not actually kill the bacteria, but keep them away from reproducing and allow the body’s own defence to kill them.

          Unfortunately, the sulfa drugs do not act on all the bacteria that cause diseases. However, they are very effective in the treatment of pneumonia and meningitis. They have little effect on tuberculosis bacteria. Moreover, they are toxic and cause many side-effects such as nausea and skin blisters. Although these medicines are found in common use but the antibiotics have been proved more effective. The sulfa drugs and antibiotics save thousands of lives every year, throughout the world. 

          A tape recorder is a machine that records sound waves into a magnetic pattern on a tape. When the pattern played back reproduces the original sound.

          A person whose voice is to be recorded is asked to speak before a microphone which converts the sound into an electric current. Since this current is very weak, it is amplified by an amplifier. The current is then passed through the recording head of the tape recorder. A current passing through the coil produces a magnetic field. Since the current is alternating in nature, so it produces a varying magnetic field. During the recording, the tape moves past the recording head. The plastic tape is coated with a magnetic substance like iron oxide and so, it is called a magnetic tape. The varying magnetic field in the recording head which is in accordance to the sound produces a magnetic pattern on the tape.

          This is how the sound is recorded on the tape in the form of a magnetic pattern.

          The tape can be played back over and over again. To play back the tape, it is again fed past the recording head. This head now acts as the playback head. As the tape moves, its magnetic pattern causes the current to flow through the coil in the head. As the magnetic field on the tape varies, the current in the coil also varies. The current is then amplified by an amplifier and fed to a loud speaker. The loud speaker changes the current into the original sound and thus we listen to the recorded voice.

          The sound recorded on a tape can be erased by an erasing head.

          The recording described above is called single track recording. Nowadays two or four track recorders are available which produce stereophonic sounds.

          In the last few years, cassette tape recorders have become very popular. The reel of the tape and the take-up reel are both held in a plastic case called a cassette. To record or play back, the cassette is simply placed in the record player and the correct switch is pressed. 

          Perfume is a blend of substances made from plant oils, flowers and synthetic materials which produce a pleasant smell. People use perfumes to make themselves smell sweet and more attractive. But in the days when standards of hygiene were poor, perfumes helped to disguise many unpleasant smells.

          The word perfume comes from Latin, per fumum which means ‘from or through smoke’. The earliest makers of perfumes burnt aromatic woods and gums, using their perfumes at religious ceremonies. The art of making perfumes was known to the ancient Chinese, Indians, Egyptians, Israelites, Arabs, Greeks and Romans.

          A perfume is made of the flowers, leaves, stems, roots or even wood turned into liquid form. This fragrance consists of tiny drops of essential oils, and it is the perfumer’s art to extract these.

          Modern perfumes are a mixture of real and artificial flower oils, alcohol and fixatives, which ‘fix’ the fragrance and make it, last for a long period. Some ingredients are taken from animals such as musk from the musk deer, castor from the beaver, civet from the civet cat and ambergris from the sperm whale.

          Thus raw materials used in making perfumes include natural products of plant and animal origin and synthetic materials. These substances are mixed in a particular proportion to obtain the desired perfumes. A good perfume may contain as many as two hundred ingredients. Essential oils obtained from plant materials are often extracted by steam distillation. Certain delicate oils may be obtained by the use of solvents. The blending of various ingredients requires great skill and a perfumer takes many years to learn his art. Perfumes are generally classified according to one or more identifiable dominant odours. The floral group blends such fragrances as jasmine, rose, lily and gardenia. The woody group consists of khuskhus, sandalwood and cedarwood. France produces the maximum quantity and the best quality of perfumes in the world.