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Category Science & Technology

What is stereophonic sound?

          The sounds we hear with our two ears are known as stereophonic sound because they give the exact idea of angular and lateral position of the sound source.

          The sound signals reaching one ear are generally slightly different from those reaching the other. Their arrival times and intensities are also slightly different. Our brain is able to distinguish the differences in intensity and arrival time of sound waves at each ear. In fact, it can discriminate arrival time differences even as small as less than 1 milli second. If a pair of microphones is placed in front of a sound source, it will receive sounds with differing intensities and arrival times depending upon the position of the source relative to each microphone. When these separate, sounds are reproduced by a pair of loudspeakers, the listener’s brain is able to use the reproduced time and intensity differences to locate the original sound. Such sounds localized in space by the brain are called phantom images. The ability of the listener to perceive phantom images is called stereophonic sound. Thus with our two ears, we are able to locate exactly both the angular and lateral positions of sound. The listener feels that he is actually present at the place of performance.

          Stereophonic sound recording and reproduction requires two or more independent channels of information. It has been observed experimentally that a minimum of two sets of microphones and loudspeakers give satisfactory auditory perspective. Separate microphones are used in recording, and separate speakers in reproduction.

          At the time of a stereo-recording two microphones are used, one of which receives more sound from the left, and the other from the right. The sounds detected by each are kept entirely separate and are encoded in two completely independent channels of the programmes. Stereo-production needs two separate loudspeakers.

          There are three basic techniques for stereophonic sound pick-up; coincident, ‘spaced apart’ and ‘individual instrument’ or close miking. The coincident technique employs two microphones located very close together. In ‘spaced apart’ technique, microphones are placed several feet apart, ‘close miking’ technique involves use of several microphones, and each located close to one instrument. The outputs are recorded on tape. The reproduction loudspeakers should be identical and capable of broad-frequency response without distortion.

          The effectiveness of stereophonic reproduction was demonstrated as early as 1933. Two track stereophonic tapes for domestic use became popular in the 1950s and single groove two channel stereo-discs in 1958. In the early 1970s quadraphonic system, employing four independent channels of information, became commercially available.

What is Heavy Water?

          We know that ordinary water is a compound of hydrogen and oxygen. It has two atoms of hydrogen and one atom of oxygen. Heavy water is a compound of deuterium (an isotope of hydrogen) and oxygen.

          In fact, hydrogen has three isotopes: protium (ordinary hydrogen), deuterium (heavy hydrogen) and tritium. Protium nucleus contains only one proton, while deuterium nucleus contains one proton and one neutron and the tritium nucleus contains one proton and two neutrons. Naturally occurring hydrogen contains 99.985% of protium, about .015% deuterium and about 1 part in tritium. Tritium is radioactive in nature. When deuterium combines with oxygen, it gives heavy water or deuterium oxide.

       

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What is an Atomic Clock?

          Since long, man has used clocks and watches to measure time. But those were crude watches and didn’t measure time accurately. A few years ago, scientists were able to develop a very sophisticated clock known as ‘Atomic Clock’. With its development a new era has been ushered in the field of time measurement. It is a wonder clock that remains accurate to one second for 1,700,000 years.

          Today we have mainly three types of clocks and watches: mechanical, electrical and electronic. Mechanical clocks and watches are spring driven; electric clocks are battery powered and the electronic ones are quartz based. All these clocks and watches show time quite accurately. But if they run continuously for long periods, they can get slow or fast.

          Now the smallest internationally accepted unit of time is the atomic second. It is based on atomic clock, and defined as the time interval during which exactly 9192631770 cycles of the hyperfine resonance frequency of the ground state of the caesium atom occur. Prior to this the second was the standard of time which was measured as a portion of earth’s rotation as 1/86400th of a day. 

          An atomic clock uses the frequencies produced by atoms or molecules. The time is measured by counting the number of vibrations. Most of the atomic clocks make use of frequencies in the microwave range from about 1400 to 40,000 MHz

          In 1947, an oscillator controlled by frequencies of ammonia molecule was constructed. An ammonia controlled clock was built in 1949 at the National Bureau of Standards, Washington D.C.

In 1955, a caesium-beam atomic clock of high precision was first put in operation at the National Physics Laboratory, Teddington, England. After that a number of laboratories started producing commercial models of caesium-beam atomic clocks.

          In the caesium clock, the caesium is heated in a small oven. The caesium produces a beam which is directed through an electromagnetic field. The 5 MHz output from a quartz clock is multiplied to give 9192631770 Hz that controls the electromagnetic field. Part of the 5 MHz output is used to derive a clock display unit which indicates time.

          During recent years, some other atomic clocks have also been developed which make use of ammonia maser, hydrogen maser and rubidium gas cells. Atomic clocks of 1960s were very large in size but by 1978 their sizes have been sufficiently reduced to fit in a small box.

          Atomic clocks are being used as standard of time. They are also being used in some sophisticated navigation systems and deep space communications. 

How does a film projector work?

               A projector is an optical instrument that shows on screen, enlarged pictures of slides or movies. Do you know how does this instrument work?

               The projector in its simplest form consists of (i) a light source (ii) a concave reflector that focuses light (iii) a condenser lens and (iv) a projector lens. A powerful light source is needed to project images on to a screen. Most projectors use an incandescent ribbon lamp of 1000 watts. A highly polished concave reflector is placed at the back of the light source so that practically, the entire light is reflected towards the slide. The light so reflected is allowed to fall on a condenser or focusing lens. This lens is a combination of two planoconvex lenses, placed in such a position that their convex surfaces face each other. The condenser lens converge the divergent beam of the light, and throws it on the slide. The condenser lens helps to strongly illuminate the image. The concentrated rays then pass through the photographic slide or film that is placed upside down in a frame. The final or projector lens is a convex lens and is kept near the slide. It reverses and enlarges the picture of the slide and throws it on to the white opaque screen. The slide shown is systematically removed by the touch of a button and replaced by a new one. Slide projectors are also used by teachers and business people to illustrate subjects under discussion.

               Movie projectors have electrically powered reels that move the film between the bulb and projecting lens at a speed of 32 films per second, so that images appear continuous to the eyes. Sprockets in the projector pull the film into the film gate. The film then stops for a moment and light from the lamp passes through the frame. The lens projects the picture on the screen. The sprockets then turn and advance the film. As the film moves, the blade of a rotating shutter passes between the lamp and the film so that the movement of the film does not show on the screen.

               In sound film, light from the lamp passes through the sound track and strikes a light sensitive cell which produces an electric signal. It goes to an amplifier and loud speaker which provide the sound. In some cases, the sound is recorded on a magnetic strip along the film as in a video recording.

 

What are quarks?

            All matter is made up of small particles called atoms. These atoms are very tiny particles and cannot be seen with the naked eye. Atoms are made up of still smaller particles called electrons, protons and neutrons, which are known as subatomic or elementary particles. Physicists have discovered hundreds of other elementary particles such as mesons, muons, neutrino end positrons. Can you imagine a particle even smaller than these elementary particles?

            A few years ago, scientists discovered that elementary particles are made up of extremely small particles called quarks. So far quarks are only hypothetical particles and have not been observed in experiments. With the exception of protons, electrons, muons and neutrino, all elementary particles are made up of different quarks. This idea was suggested in 1964, by two American physicists, Murray Gell Mann and George Zweig. 

           There are probably four different kinds of quarks, carrying a fractional charge. Each has an anti-particle called anti-quark. Until 1974, only three types of quarks were known; two of very nearly equal mass, of which the proton, neutron and pi-mesons are composed, and a third, bigger quark which is a constituent of K-mesons and hyperons. These quarks are called the up quark (u), the down quark (d) and the strange quark (s). In 1974, one more quark, named charm quark (c) was also predicted. The existence of two other types, top quark and bottom quark, is also predicted.

             The charges of the four quarks u, d, s and c are +2/3, -1/3, -1/3, and +2/3 that of the electron charge.

             Anti-quarks have opposite charges. All quarks and anti-quarks have equal spin which is 1/2.

             These quarks combine to form different elementary particles. For example, protons are composed of three quarks (uud) and neutrons also of three quarks (udd). Each meson can be conceived as the union of a quark and an anti-quark.

 

What is a Robot?

          A robot is an automatic machine which can work like a human being. It can replace man in various branches of scientific and industrial tasks because it does not suffer from human limitations. It may or may not resemble a human being but definitely can work like a human being. The robots which resemble humans are called androids.

          The word ‘robot’ was first used in the play ‘Rossum’s Universal Robots’ by the Czechoslovak dramatist, Karel Capek, who had derived it from a Czech, word ‘Robota’ which means a forced or bonded labourer.

          The industrial revolution and automations stimulated the invention of robotic devices to perform certain human tasks. A human worker, however superb a craftsman he may be has certain limitations. He cannot work continuously in a hostile environment. He cannot work for long periods because he gets tired. He may be in short supply and may be expensive to hire. Modern industrial robotic devices aim to substitute a machine for man in hostile environments, cut costs by replacing expensive hand labour with cheap dependable machines, and provide versatile, all purpose robots or mechanical devices at predictable costs. Robot is such a machine which does not get tired, does not go on strike and does not demand increase in salary. 

          Robots can perform a variety of jobs such as welding and painting a car, house cleaning, cutting the grass of a lawn, working in nuclear plants or travelling to space. They can also play chess, work as a watchman, cut the wool of a sheep and pluck fruits from trees.

          Robots of higher level are capable of adapting to changes in environment. They are also capable of making decisions with the help of computers. A more complex robotive device in modern transportation is the automatic aircraft pilot which can control routine flights. An android robot named Shaky Robot was developed at Stanford Research Institute in California to do a variety of research jobs.

          Japan has the largest number of robots in the world. The United States of America, Britain, Germany, Sweden, Italy, Poland, France, India, etc are also using robotic devices for different purposes. All robotic devices are controlled by computers.

 

What is pasteurization?

          Normally if fresh milk is not boiled for sometime it becomes sour. But this does not happen with boiled milk for several hours. Do you know why it is so?

          Fresh milk contains several types of bacteria. When milk comes in contact with air, the number of the bacteria multiplies very fast. These bacteria turn the milk sour. The bacteria come to the milk from three different sources. First, if the cow or the buffalo from which the milk comes is suffering from some disease it might be excreting bacteria in its milk. The tuberculosis germs are transmitted from cattle to man in this way. Secondly, the milkman could have certain infectious disease and might contaminate the milk while milking the cow. Thirdly, the water used to wash the milk pot or the teats of the cow or buffalo may have germs in it. The bacteria transmitted to the milk from any of these three sources grow very fast and spoil the milk.

          Pasteurization is a process for sterilizing milk and other drinks invented by Louis Pasteur (1822-1895) – a French micro-biologist and chemist, for improving storage qualities and to protect them from spoiling. This method is named after him. The milk and butter sold in the market are normally first pasteurized, and then marketed.

          In the process of pasteurization, milk, wine, butter etc. are heated up to a certain temperature and then quickly chilled. This kills the bacteria in them. If milk is heated up to 63° for 30 minutes in between 72°- 85° for 16 seconds and then chilled to 10° or less, the bacteria present in it are destroyed. Pasteurization not only protects the milk from being spoiled but also kills the bacteria of tuberculosis and other diseases. Pasteurized milk can be kept unspoiled for a longer time without boiling. The process does not affect the taste of the milk.

          Nowadays gamma rays and beta rays are also being used for pasteurization. These rays kill the bacteria present in the milk and other drinks. 

What are infra-red radiations?

          We know that the sunlight consists of all those colours which are seen in a rainbow. These colours are: violet, indigo, blue, green, yellow, orange and red. Light from the sun travels in the form of waves which are known as electromagnetic waves. The different colours of light have different wavelengths. Our eyes are sensitive only to the wavelengths relating to the above seven colours. Apart from the wavelengths of these seven colours, the sunlight consists of radiations of other wavelengths also, but our eyes are not sensitive to them. Rays having wavelengths higher than of red light are called infra-red rays and those lower than violet light are called ultraviolet rays. Both infra-red and ultraviolet rays are not visible to our eyes. 

          Infra-red rays come not only from the sun but from every hot object. Burning wood and coal, electric heater – all produce these rays. Infra-red rays were discovered by the British astronomer Sir William Herschel in 1800. In fact all objects give of infra-red rays according to their temperature. The warmer an object is, the more infra-red rays it gives off. These can be recorded on special type of photographic films made of infra-red sensitive materials. Whenever these rays fall on any material body they produce heat. They are very useful to us.

          Infra-red radiations are being used for the treatment of several diseases. Special types of infra-red lamps are used for treating the pains of muscles and joints – especially for back pain. They are also used for heating rooms in winter.

          Infra-red radiations are being used for the guidance and control of missiles and other ballistic weapons. These radiations are also used for transmitting and receiving invisible signals. Molecular structures are studied with the help of these radiations. Impurities present in the materials can also be detected by these rays. Infra-red absorption spectroscopy is an important analytical tool in organic chemistry.

 

How are millions of substances made from only a few elements?

          The number of naturally occurring stable elements on the earth is 92 only. Although scientists have so far discovered 107 elements in all, but 15 of these have been artificially made in the laboratories. These artificial elements are unstable in nature. The atoms of these 92 elements are also of 92 kinds only. Do you know how millions of substances are made from these elements?

          All substances available in the universe are made by the combination of atoms of these 92 elements. The atoms of different elements combine with one another in various proportions and keep on forming countless substances. Some of the important elements are: iron, gold, silver, copper, aluminium, sodium, potassium (metallic elements), oxygen, nitrogen, chlorine, carbon, sulphur (non-metallic elements). All the elements consist of atoms and the atoms of the same elements are alike. Two or more atoms combine with each other to make molecules. For example, two atoms of hydrogen combine with one atom of oxygen to make one molecule of water. Even a very small quantity of water consists of innumerable molecules. Similarly one atom of sodium combines with one atom of chlorine to make one molecule of the common salt sodium chloride. 

 
 
 
 
 
 
 
 
 
 
 

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Which material does not burn in fire easily?

          Whenever any substance is put in to fire it burns and changes into ash. But asbestos is one such material that does not burn in fire. That is why the fire fighters wear clothes made from asbestos when fighting large fires. In fact their clothes, shoes, gloves, helmets etc. are all made from the fibres of this material.

          Asbestos is a Greek word which means ‘inextinguishable’ or ‘unquenchable’. The invention of this material is not new. The Romans used asbestos sheets 2,000 years ago for wrapping dead bodies in order to preserve them.

          This material is obtained from mines. It is formed by the dissociation of olivine. Olivines are the silicates of calcium and magnesium. Due to certain chemical reactions in the mines, olivine changes into fibres of asbestos. Asbestos obtained from mines is first dried and then its fibres are separated with the help of machines. These fibres are woven into threads and ropes which are then used for making clothes, sheets, mats etc.

          Asbestos is a very useful material. It is used for making fire-proof clothes, paper and as heat-insulator in furnaces. It is also used for making fire proof tiles for buildings. In cold countries, water pipes coated with this material which serve as insulators preventing water from freezing in the pipes.

          It is a bad conductor of both heat and electricity and is least affected by acids and alkalies. It does not burn even at a temperature of 2000°C to 3000°C. Some special varieties of asbestos are now available which do not burn even at 5000°C. This variety is used in research laboratories. The most common mineral of asbestos is chrysotile found in Canada and Russia.

          Canada is credited with 75% of the total world production of asbestos. America manufactures maximum number of items from asbestos though the raw material obtained in this country is only 5%.