My Science School

Man has been using soap and water as cleaning agents for thousands of years. The first soap was made in the middle east about 5000 years ago. The discovery of soap less detergents is not very old. The first synthetic detergent was not invented until 1916, but since then the manufacture of non - soap detergents became a major development of the petrochemical industry. New methods of fabric cleaning came into use, such as dry cleaning.

Dry cleaning is a method of cleaning fabrics with chemical solvents instead of soap and water. Many of these solvents are derivatives of crude oil. Petrol is the most important of them. Benzene is also used in dry cleaning. Their fumes can be dangerous if inhaled and they catch fire easily. Some safer synthetic chemicals such as polychloroalkanes and alkanes have also been developed. The most common dry cleaning chemicals are carbon tetrachloride and trichloro ethylene.

In a dry cleaning establishment, clothes are usually treated first for stains. Then they are placed in the dry-cleaning machine with the cleaning fluid or solvent and tumbled slowly for up to half an hour. After a rinse in clean fluid, the clothes are spun around rapidly to extract the liquid, and are finally fluffed in hot air. Any stains remaining are removed by hand and clothes and then steam pressed.

Dry cleaning has several advantages over ordinary soap cleaning. Cleaning fluids can dissolve stains (especially oil and grease) which soap and detergents cannot remove. The process is most useful for delicate or expensive silken and woollen fabrics because it does not have any undesirable effect on them. For instance, the colours do not fade, as they might in water. 

          Quartz is a hard, glossy mineral made of silicon and oxygen. It is found in most kinds of rocks in colourless, often transparent form. There are also coloured varieties including semi-precious stones such as amethyst and citrine. Pure quartz is called rock crystal also. In appearance it looks like glass. It has six sided crystalline structure. It ranks 7 on the Mohs’ scale of hardness and is resistant to chemical or mechanical breakdown.

          Quartz is extremely hard and will scratch glass. It melts at a very high temperature. It can be made into tubes, sheets or blocks. It can also be blown into various shapes by using oxy-hydrogen flame.

          Quartz has great economic importance. Sandstone, composed mainly of quartz, is an important building stone. Large amount of quartz sand is used in the manufacture of glass and porcelain and in metal casting for foundry moulds. Quartz is used as an abrasive in sandpaper and grindstones. It is used to make prisms and lenses which can transmit ultra-violet light. Tubing and various vessels of fused quartz have important laboratory application. It is also used in ornamental work and industry where its reaction to electricity makes it valuable in electronic instruments. Quartz fibres are used in extremely sensitive weighing devices.

          Quartz is a piezoelectric material, i.e. when pressure is applied across the two surfaces of a quartz crystal, an electric voltage develops across the crystal and when voltage is applied across the two faces of the crystal, and it expands, or contracts. Due to this property, it can help to change electric signals into sound waves and vice versa. The piezoelectric property of quartz plays an important role in radios, television and radar. Quartz oscillators are used in Quartz crystal watches to give accurate time.

          Natural quartz crystals of commercial grade are obtained from Brazil. Quartz can also be made synthetically.

 

          The unique feature of a video-tape recorder (VTR) is that it plays back both sound and picture. It is mainly used to record television programmes as magnetic patterns and play video cassettes. But how does the video-tape recorder work?

          A video-tape is a band of plastic tape. On one side, it is coated with a film of magnetic iron oxide whose thickness is about one-five thousandth of a centimetre. The width of the tape is about 1.25 to 2.5 cm. For recording a programme, the tape is run by a magnetic video tape recorder.

          A television camera changes an image into electrical signals. At the same time, a microphone changes sound into electrical signals. These signals are then fed into the recorder. The VTR contains recording heads that convert the signals into varying magnetic fields. As the magnetic tape passes these heads, they produce magnetic patterns on the tape. This tape can then be used to reproduce the original sound and picture. When the tape is played back, the changing magnetic fields of the pattern of iron oxide particles create weak currents which exactly correspond to the recorded sound and picture.

          The sound and picture signals are kept separated in the recorder, and are recorded on to different parts of the tape. Usually, the sound signal is recorded on to a narrow track at the top of the tape. The image signal is recorded on to a wider track in the middle of the tape. A control signal is recorded along the bottom of the tape. Television studios generally use 5 cm-wide tape. The tape moves at a speed of 37.5 cm a second.

          The head that records the image signal rotates, as the tape passes by it. As a result, the recording is made in diagonal bands across the tape. This allows more information to be stored on a given length of tape.

          Video tapes are used to record and reproduce various television programmes. They are also used for the reproduction of sport events during a live broadcast. Video tapes are also used in slow motion and stop-action techniques. Nowadays video discs having pictures as well as sound recordings are also available to see a film on the disc, by playing it on a video disc player connected to a television set. 

          Radio and television stations make use of microphones. They are also used in public address systems and in motion pictures and phonograph records. The mouth piece of a telephone is a simple type of microphone. Let us see what exactly a microphone is.

          A microphone is a device which converts sound waves into electrical signals. These signals can then be broadcast through the air or sent over to distant points, where they can again be converted back into sound.

          Microphones can be divided into two groups depending upon how they respond to sound waves. These are: the pressure type and the velocity type.

          The pressure type microphones contain a thin metal plate called a diaphragm. This is stretched like a drumhead inside a rigid frame. The diaphragm is a part of the electrical circuit. When the sound waves strike the diaphragm, it starts vibrations at the same rate as the sound waves. These vibrations produce corresponding electric signals by changing the electric current that flows through the circuit.

          The pressure microphones are of several types, such as condenser microphone, moving coil or dynamic microphone, the crystal microphone and the carbon microphone.

 

Continue reading "How does a microphone work? "

               A mass spectrograph is an instrument used to analyze the constituents of substances. It not only detects different kinds of atoms and molecules present in the substance, but also finds out their relative amounts. By the use of electric and magnetic fields, it separates ions of different masses. Do you know how this instrument works?

               The working of the mass spectrograph first involves the change of the substance into a gas, which is passed into a vacuum chamber. A beam of electrons is bombarded to change the gas atoms and molecules into ions. The ions are then accelerated, by passing them through an electric field. Then the ions are passed through a magnetic field, where they get deflected. The positive ions are deflected one way, and the negative ions in the opposite direction. The amount of deflection is inversely proportional to the masses of the ions. The heavier the mass, the lesser the deflection. This separates ions of different masses. Ions of the same mass and charge stay together. The ions are then allowed to fall on a photographic plate. Different ions hit the plate at different places and as a result, this photographic plate records the amounts of various atoms and molecules. Photographic plate is used to identify different ions which have hit it. From the intensity variations on the plate, we can know the relative amounts of atoms or molecules present in the substance. 

               The mass spectrograph was developed by a British scientist, William Francis Aston. He was awarded the Nobel Prize in 1922 for this invention. After this, several other mass spectrographs were developed by many leading scientists like Dempster, Bainbridge, Nier, etc but all were just modifications of Aston’s mass spectrograph.

              The mass spectrograph is widely used in geology, chemistry, biology and nuclear physics. It is a very useful instrument for isotopic studies. Aston himself discovered 212 of the 287 naturally occurring isotopes. Mass spectrographs are also used as vacuum leak detectors.

 

In 1960, very strong radio emissions were observed by an American astronomer, Allan R. Sandage to be coming from certain localized direction in the sky. When viewed on the photographic plate, they appeared like stars. But they were not stars, as proved by their other characteristics including a large red shift. The accurate position measurement of these star like objects on optical photographs, led to the discovery of a new class of objects in the universe, the quasars (quasi-stellar sources).

They appear star like on the photograph because their angular diameters are less than about 1 second of an arc, which is the resolution limit of ground-based optical telescopes. Since stars also have angular diameters much less than this, they too appear unresolved or point-like on a photograph.

In 1962 a much brighter star like object 3C273 was identified by Maarten Schmidt with the help of a radio telescope in Australia. Its red shift was found to be 0.158. This red shift turned out to be far larger than any other that had been detected for ordinary galaxies. These observations established the existence of quasars beyond doubt.

Quasars are generally much bluer than most of the stars, except white dwarf stars. The blueness of quasars, as an identifying characteristic, led to the discovery that many blue star like objects have a large red shift, and are therefore quasars. Till today scientists have studied more than 1000 quasars but their nature and distance from earth remain a puzzle.

Quasars consist of a massive nucleus with a total size of less than a light year, which is surrounded by an extended halo of gas excited by the energy radiated by the central object. The central object emits radiation over a wide spectral range. Some quasars emit significant amount of energy at radio frequencies ranging from about 30 MHz to 100 GHz. It is believed that the energy emitted by quasars is gravitational and not thermonuclear in origin. More than ergs of energy are released in quasars over their life-time.

Till to day scientists have not been able to measure the exact distance of quasars from the earth. Various similarities of quasars with radio galaxies strongly suggest that quasars are also active nuclei of galaxies might be associated with the birth of some galaxies. Studies have shown that quasars must have been much more common in the universe about many years ago.

 

          We are all aware of the damage and disaster a fire can cause in certain situations. Now let us see how to control a fire and prevent it from spreading.

          A fire is basically a chemical reaction during which heat and light are produced. Three factors are necessary for a fire to start – fuel, oxygen or air, and heat to raise the temperature of the fuel to its ignition temperature.

          A fire can be extinguished when one or more of these agents is removed, i.e. fuel, supply of air and lowering the temperature of the combustible substance. All fire extinguishing methods make use of these principles.

          The original fire extinguisher, a bucket of water, is still useful in controlling many types of fires. The principal effect of water on a fire is to cool the burning material, thus removing the heat – one of the factors without which combustion cannot continue. It can be applied in a variety of ways such as by flooding the fire with water. Jets of water are used to knock down the flames of fire, and sprays are used to absorb heat and drive back smoke and gases.

           Another common extinguisher is the soda-acid type. It sprays a mixture of water and carbon dioxide on the fire. This is based upon the principle of cooling the burning material and cutting the supply of air by non-combustible carbon-dioxide.

           In this extinguisher a solution of sodium bicarbonate is placed in a cylindrical vessel of steel. Sulphuric acid is kept in a bottle in a small compartment made within the cylinder, near the top. When required, the knob is hit against the floor. This brings the sodium bicarbonate and sulphuric acid in contact with each other. Immediately carbon dioxide is formed and it comes out of the fire nozzle which is directed towards the fire. These extinguishers are useful only for small and localized fires. They are not effective against gasoline, oil and electrical fires.

           Foam extinguishers are based upon the principle of cutting off the supply of air by forming a fire-proof coating of foam around the burning material. In this, a mixture of sodium bicarbonate and aluminium sulphate containing licorice extract is sprayed. It produces foam and extinguishes the fire.

           The other types of extinguishers that are used on oil and electrical fires are: Carbon dioxide extinguishers, dry-chemical extinguishers and vaporizing liquid extinguishers.

           Water should never be used for extinguishing electrical or oil fires. In case of electrical fires, it can cause electrocution. If water is used on burning oil, the oil simply floats on top of water and continues to burn. As the water flows away, it can carry the oil with it and so spread the fire.

           Fire extinguishers are provided by law in all public buildings, factories and schools. Most of the big cities have fire brigades for fire prevention and control.

 

          The polaroid camera is also known as the ‘instant camera’ because it takes pictures and develops them in a matter of minutes. It was invented by Edwin H. Land of the United States and the first polaroid camera was sold in 1948. At that stage, it took only black and white photographs. Later, another camera was built that could take pictures and develop colour photographs.

          Polaroid cameras are loaded with a double picture roll. One part is a negative roll of the film, and the other a positive roll of a special printing paper. Small pods (containers) of chemicals are joined to the positive roll. After exposure to light through the camera’s lens, the negative and positive rolls are made to pass through a pair of rollers that break the chemical pods. The chemicals flow over the exposed portion of the negative roll and develop a negative image on the roll – the parts of the picture that should be black are white, and the parts that should be white are black. More chemical reactions take place between the pod chemicals and the chemicals coated on the positive roll, and a positive photograph is made – the white areas in the photograph are printed white and the black areas black. This process takes about 10 seconds for a black and white photograph and upto a minute for a colour one. 

Continue reading "How does a polaroid camera take instant photographs? "

               We all know that electricity travels from one place to another through metallic wires. Can light travel through wires too?

                Light can also travel through wires, but these wires are not made of metals. They are made of glass or plastics. Light carrying wires are extremely thin and are called optical fibres. The branch of science dealing with the conduction and study of light through fibres is called Fibre Optics.

       In 1870, a British physicist John Tyndal showed that light can travel along a curved rod of glass or transparent plastic. Light travels through transparent rods by the process of total internal reflection. The sides of the fibre reflect the light and keep it inside as the fibre bends and turns. 

 

 

               The narrow fibres have a thin core of glass of high refractive index surrounded by a thin cladding of another glass of lower refractive index. The core carries light and the covering helps bend the light back to the core.

               Fibres are drawn from thick glass rods in a special furnace. The glass rod of higher refractive index is inserted in a tubing of glass of lower refractive index. Then the two are lowered carefully and slowly through a vertical furnace and the fibre drawn from the lower end is wound on a revolving drum. With this method, fibres of about .025 mm in diameter can be drawn.

               Fibres so prepared have to be aligned properly in the form of a bundle. They should not cross each other; otherwise the image transported by it will be scrambled. They are kept in straight lines. Once the aligned bundle is made, it can be bent or turned in any desired direction. 

 

 

Continue reading "Can light travel through wires? "

     

    Perfumed talcum powder is used by a large number of people throughout the world to protect the skin from heat during the hot summer months. It gives a soothing effect to the skin. Do you know what this talcum powder is?

     

    It is a fine perfumed powder made from mineral called talc. Talc is the softest mineral known to man. When it is in solid form, it is called soapstone and is usually grayish or greenish in colour, and very soft and greasy to touch. Often it has brown spots. To make talcum, white-coloured soapstone is first ground to a very fine powder. Then this powder is sieved to remove the coarse grains. Desired scents are added to this sieved powder. Finally it is packed in tin or plastic containers for sale. 

 

          One of the remarkable features of talc is its simple, almost constant composition. It is basically magnesium silicate. Soapstone is often used in the making of household articles because it resists heat and can easily be shaped. Cooking utensils and parts of stoves are sometimes made from it. It is also used in the making of laundry tubs. As soapstone hardens at high temperatures, it is also used for lining furnaces. As it cannot easily be eaten away, slabs of this material are used for acid tanks in the laboratories. It is a poor conductor of electricity and for this reason is used as a base for switch boards and electrical insulation. 

          The best quality talc comes from Italy. Its deposits are found in England, Canada, Germany and Rhodesia. The Atlantic Coast has more talc than all the other countries of the world. About three quarters of the talc processed in the West goes into the manufacture of paints, glazed tiles, ceramic products, paper and rubber. 

          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.

          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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          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. 

               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.

 

            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.