My Science School

          Star television is the popular name of satellite television. A broadcasting transmitter on the ground can transmit signals only to a limited distance. Even if the transmitting antenna is on a tall mast, hills and valleys in the landscape can soon block the signals. The television satellite can be taken as an antenna on an incredibly tall mast - so tall that it is in space.

          Satellites are being used for many years by TV stations to exchange TV programmes among each other. The signals are beamed out from earth station to spaces which are picked up by the aerial of the satellite. These signals are re-transmitted by the satellite down to another part of the earth where they are received by the dish antenna. The receiving TV station then transmits the signals to viewers in the usual way. In this way, TV signals are sent from one part of the world to the other. TV transmission from one earth station to the satellite and back to another earth station. Sports events are transmitted in this way.

          The latest development is direct broadcasting by satellite, known as D.S.B., where the signals go straight to the viewers. For this, you need a special dish aerial like the one shown here to pick up D.S.B. TV.

 

         Canning of food is one of the methods of food preservation. The food that is stored in cans has to be made sterile and free from germs to keep it fresh. Canning also involves keeping air away from food because it would bring germs to it.

         In a canning factory, the food is prepared in large containers. It is heated to destroy micro-organisms and to stop enzyme activity. Most germs-killing temperatures range from 100°C to 121°C. Meat, fish and vegetables are heated at about 120°C. The sterilizing time depends on the temperature, the container and the type of food.

         The food after heating goes to the canning machine, which is fed with a line of empty cans. The food is filled in the metal or glass containers with a liquid, such as, sauce or sucrose syrup. Air is removed from the containers and the containers are then sealed with air-tight lids. For some foods the cans and food are sterilized first by heating before the cans are filled.

         Most canned food can be kept for more than a year. The other methods of food preservation are cold storage, freezing, drying, freeze-drying and curing. All these methods are based on modern science and technology. All methods of food preservation are performed with extreme cleanliness and hygienically. 

A dishwasher is a modern domestic appliance that cleans and dries utensils automatically. These machines generally worked on the principle of passing the dirty dishes under jets of hot water by means of conveyor belt or revolving basket. Modern dishwashers have reversed the procedure. In these dishwashers the utensils are cleaned by revolving jets of water above and below the basket.

                  A modern dishwasher contains heater, pumps, motors etc. and requires a water supply. It is housed in a enameled cabinet. A drop down door enables the plastic coated basket to be pulled out on slides or rollers for loading. The door is fitted with a micro switch to shut of all operations.

                  A dish washer generally has several programmes which may be selected by means of keys or push buttons, depending on the type of utensils to be washed and the type of food residues to be removed. In a typical programme, dirty crockery and cutlery are loaded into specially designed carriers. To wash and rinse, water is sprayed from above and below the dish basket by whirling arms through which the water is pumped, each of the arms have several spray holes in it. The pressure of the water itself makes the jets spin around. The first part of the cycle uses water containing detergent to dissolve grease and grime. The detergent is loaded into a compartment in the lid which automatically releases the right amount at the proper point in the cycle. In the second part of the cycle, clean water rinses away the soapy water. Then a heating element warms and dries the utensils.

                A timing device automatically controls the selected cycle, it is often operated by means of round calibrated knob. Some machines have pilot lights which indicate the part of the cycle in operation. These machines are proving very useful as kitchen aids.

 

          A washing machine is an electrically operated machine used to clean dirty clothes. Most washing machines have a round drum that spins to wash the clothes. The clothes tumble over each other as it turns, which helps the detergent to clean them.

          In a modern washing machine, a set of buttons allows the user to select a pre-programmed cycle of washing, rinsing and removing the water. At the start of the cycle, water pours in through an electrically controlled inlet valve. Once the water reaches a certain level in the drum, this is detected by a sensor that turns off the inlet valve. The pressure of the water in the inlet pipe helps to shut the valve firmly. If required, the water is then heated by the machine’s heating element. Once the preset temperature is reached, a thermostat switches off the electric supply to the heater. The dirty clothes are cleaned by the detergent mixed in water in the spinning drum. The clothes are rinsed in clean water to remove the soapy water.

           The clothes may be washed and rinsed several times in the washing machine to get them really clean. Then they are spun very quickly to remove most of the water so that they may dry quickly. This forces droplets of water out of them by centrifugal force. After spin-drying, the clothes can be air-dried or dried in a tumble dryer.

           Washing machines, now a day, are being used on a large scale. They save time and labour of washing the clothes. 

              Plastic surgery is a branch of surgery devoted to restoration, repair and correction of malformations of tissues. It concerns not only return to normal appearance but also the restoration of function. The field of plastic surgery has several sub-divisions such as cosmetic surgery, management of congenital defects, burns, wounds and other acquired defects.

             Cosmetic surgery deals with improving the appearance of tissues or organs such as the nose, face, eyes or breasts. The most common types of cosmetic surgery are face lift to remove wrinkles from the face and neck and a rhinoplasty to change the shape of the nose.

             Plastic surgeons treat physical defects that exist since birth (congenital defects) or are caused by injury or disease. Often the body part that is defective or damaged does not work as it should. In such cases, the surgeon does reconstructive plastic surgery. This often requires grafting. In grafting skin muscle, bone or cartilage is transplanted from a healthy part of the body to the hurt or damaged part. Sometimes reconstructive surgery involves reattaching several limbs, rebuilding damaged tissues, restoring damaged blood vessels and nerves. Plastic surgeons are available almost in all the hospitals.

             Plastic surgery has been practiced for hundreds of years in China and India. Chinese and Indian doctors were reshaping noses and lips long ago.

 

            A telescope is an optical instrument used to see distant objects clearly and magnified. The telescope was invented in 1608 by a Dutch optician Hans Lippershey. In 1609, the Italian astronomer Galileo made his first telescope and observed the rings of Saturn and Jupiter’s moons. Today there are three main kinds of telescopes: refracting telescopes, reflecting telescopes and radio telescopes.

Refracting Telescopes: A refracting telescope makes use of two lenses fitted at the end of a tube. An astronomical telescope consists of one larger size convex objective lens and a convex eyepiece while a Galilean telescope makes use of a convex objective lens and a concave eyepiece. Modern refracting telescopes usually contain complicated lens systems to correct chromatic aberrations.

Reflecting Telescope: A reflecting telescope is made of a concave mirror that gathers and focuses light waves. Another mirror near the point where waves come together reflects light into the eyepiece.

            A Newtonian telescope uses a mirror set at a 45° angle to reflect the light into the eyepiece. A Casegranian telescope has convex mirror which reflects light through a tiny hole in the centre of the objective mirror. The light passes through to the eyepiece, which makes the image larger.

           The largest reflecting telescope in the world is at the Yerkes observatory in Wisconsin. Its objective lens has a 102cm diameter. The Palomar observatory in California has a reflecting mirror with a diameter of 508cm.

Radio Telescopes: A radio telescope has a huge reflector shaped like a bowl which reflects radio waves to a detector. Radio telescopes are used in astronomy. These telescopes can be used under all weather conditions.

            Plastics do not occur naturally but are manufactured. The word ‘plastic’ has originated from the Greek word ‘Plastikos’ which means ‘to mould’. It is made from simple organic chemicals. It has many varieties and colours.

            Plastic was invented by Alexander Parkes of England in 1862. In those days it was called ‘Parkesine’ after him. Parkesine was the first plastic ever produced.

            Many plastics have ‘poly’ in their names for example, polythene. Poly comes from a Greek word meaning ‘many’. Polythene means ‘many molecules of ethene joined together’.

                   The manufacturing of plastic on a commercial scale was started for the first time by Leo Hendirk Backeland. He made it from phenol and formaldehyde. Subsequently, new techniques were developed for the production of plastics. Today, scientists have discovered many raw materials which are used in the making of various kinds of plastic products. Most plastics are made from chemicals found in oil, although a few come from wood, coal and natural gas. Common types include polythene, polystyrene, PVC and nylon.

                  Today, plastic has become an integral part of our life. Its uses are endless. Transparent plastics are used for making lenses and windows of aeroplanes. Polythene bags, a plastic product, are used in almost all walks of life. Articles of domestic use like buckets, cups, brushes, combs, baskets, cabinets for radios, transistors etc. are also made of plastics. Toys and sports goods made from plastic have flooded the markets everywhere. The yarn for making Terylene cloth is, in fact, made from plastic. Today scientists have even succeeded in developing heat insulating plastics. Foam cushions, seats in trains, cars and aeroplanes - all are made from plastics. Now, plastics are used as surgical aids also. There is hardly any field of life in which plastics are not used. 

             Through the ages, man has used many methods of time measurement such as rotation of the earth, rising and setting of the sun, movement of the moon and stars and the change of seasons. Perhaps the earliest measurement of time was based on the regular cycle of night and day. The 24 hour period between one mid night and the next was called the mean solar day.

            Time measurement by the earth’s rotation with respect to the sun is called sidereal time. A sidereal day lasts 23 hours, 56 minutes and 4 seconds. The time the earth takes to complete one revolution around the sun, is called the sidereal year. The sidereal year lasts 365 days, 6 hours, 9 minutes and 9.54 seconds. Sidereal time is more accurate than solar time.

                  The oldest methods for measuring time include sundial, candle clocks, water clocks and hour glasses. In a sun dial, time was measured by the length of the shadow of a stick casted by the sun. With candle clocks, time was measured by the rate of a burning candle. The water clock was a leaking bowl. In the hour glass, sand flowed from one container into another at a steady rate. By measuring the amount of sand in either container, a person could tell how much time had passed.

The development of clocks that worked by springs started in the late 1400. The two main types of modern clocks are - mechanical clocks and electronic clocks. Mechanical clocks are powered by various devices that must be wound while the electronic clocks are battery powered. Quartz based clocks are also battery driven. Most of the quartz clocks which are based on quartz crystal vibrations are accurate upto 60 seconds in a year.

                  Digital clocks and watches which became popular in the 1970s are also very accurate time measuring devices. Most of them have liquid crystal display system or light-emitting diode display system. These are also quartz based.

                 The most accurate means of measuring time is an atomic clock. An atomic clock measures the vibrations of certain atoms of cesium or ammonia gas which keep extremely accurate time. In 1000,000 years an atomic clock may loose or gain only a few seconds. The world time changed to atomic time standard in 1972.

 

Ice, which we generally see around us, is made by freezing the water. Water turns into ice when it is cooled to 0°C. There is another kind of ice which is known as dry ice.

Dry ice is solid carbon-dioxide. It is formed when carbon-dioxide turns directly from a gas into a solid at a temperature of about - 80°C. It is so cold that if held in hand it causes frost bite. It is usually prepared by cooling carbon-dioxide under high pressure. It looks rather like snow but can be made into blocks by compressing the flakes. Dry ice is very heavy.

Dry ice is very important for cooling or refrigerating foods such as ice creams and meat and medicines. It is also used to stimulate fog and steam effects in television or stage plays because it rapidly turns back to gas at ordinary temperature without becoming liquid.

 

              Wearing a pair of spectacles is a common sight. All men, women and children, who have weak eye-sight, use spectacles. Scientists have developed spectacles that help in seeing both the near and distant objects clearly. Nowadays, lenses are used inside the eyes in place of spectacles. These are known as contact lenses. These lenses can be of different colours and are used by those who do not want to wear spectacles.

              The use of spectacles was started some 700 years ago. In 1266, Roger Bacon of England used a piece of glass to magnify the words written in a book. This glass piece was cut out of a spherical ball of glass. But it is not definitely known as to when glass pieces were used in the form of spectacles.

                     Spectacles are shown on the eyes of one Cardinal Ugon’s portrait made in 1352. This proves that spectacles were developed during the period 1266-1352. By the sixteenth century, they were very much in use. In 1784, Benjamin Franklin brought wonders in the field of spectacles by making bifocal lenses. A question must be coming to your mind as to how do we see clearly with the help of a pair of spectacles?

                     It is so simple. Our eyes act as a camera. The light rays enter our eyes through cornea (black portion of the eye). There is a convex lens inside the eye, and behind this lens there is a screen which is called the retina. The light rays coming from any object make an inverted image of the object on the retina with the help of this lens. This image is carried to the brain by the optic nerve. It becomes erected there. This is how we see an object. If the eyes have no defect, the focal length of this lens gets automatically adjusted and the image of the object always falls exactly on the retina. But, sometimes, the eyes develop some defects due to which the image of the object is formed before or behind the retina. Thus, the object appears blurred. Persons having such eye-defects need the assistance of spectacles. The defects of the eyes are mainly of three types.

 

 

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The colour of an object is determined by the spectral composition of the light reflected by it. When a surface is dry, the reflected light rays corresponding to the colour of the surface are superposed with diffused white light arising out of random scattering resulting from the roughness and irregularities of the surface. In the case of clothes, this superposition tends to fade the reflected colour.

 If clothes are immersed in water, all the kinks and interspaces are filled with water. This minimizes scattering of light on the surface. So the reflected light comes out unsuppressed with the basic hue of the cloth. Hence it looks richer and darker than when dry.

 The effect is conspicuous on cotton clothes as the fibres are loosely packed with a lot of microscopic air spaces. This increases the surface area and consequently the scattering of light. Hence cotton clothes look light when dry and dark when wet. The effect is not so much in synthetic and silk clothes as their surfaces are smoother and very little water is absorbed by them. 

 When any TV is switched on, electric power is supplied to both audio and video sections. The video section consists of a cathode ray tube which is commonly called as picture tube. An electron beam is used to sweep the screen to display the pictures. This electrons beam is generated within the CRT using a filament which can emit electrons only when heated. This heating process requires sometime. Audio section does not need any such ‘warm up’ to start functioning and so we hear the sound as soon as we switch on.

 

This technique is often used in real-life crime programmes to protect innocent individuals or to avoid suspects receiving unfair trials.

The process of pixilation works as follows: for each square pixel area, the computer measures the brightness and colour of each point and calculates the average. This average value is then assigned to the entire pixel. Thus the properties of the picture to be obscured, in this case a face, are largely retained. However, each square has sharp edges, and since the edges are a product of the pixilation process and not related to the elements of the face, they obscure the picture. The reason the face still seems to move is because although the position of each square will remain constant, the person “behind” the pixilated area will be moving, and therefore the average values for brightness and colour change. Squinting, screwing up your eyes or, even better, removing your spectacles blurs the image and prevents you from seeing the sharp edges of the squares. You are then left only with a face in which changes in brightness and colour have been smoothed by averaging, and which is then much easier to see and identify.

The same effect can be achieved by making the pixilated face smaller, or by moving it further away - the edges become too fine to observe their detail and disappear and the face is more easily seen. This effect was first described by Leon Harmon in 1973 (Scientific American, vol 229, p 70). 

The artist Salvador Dali made use of a sort of a “pixilation” technique in some of his paintings, one of which is pictured aside. These images were unreadable until one moved a certain distance from the picture or if one did some serious squinting. The pixilated painting below illustrates the point. When you view the picture from close quarters you see a woman walking through an opening. From further away, all you can see is the face of Abraham Lincoln, the former president of the U.S. With computers the effect is far more accessible. Simply take a bitmap image of anything, but preferably something small, and zoom in on it until you can see the pixels. The more you zoom in, the less clear the picture becomes, and the more you need to squint to see it.

  

     The connection between any two subscribers is through a Local Switching Exchange (or) Central Office.

It is a hard wire connection in series with the earphone and carbon microphone of each telephone handset with a battery. The Local Switching Exchange or the Central Office (CO) employs a battery plant.

 

To make a phone call, a subscriber lifts his handset (receiver), so that a switch called “off-hook” switch in his telephone set is “on”, and he gets connection with CO. The CO sends a dial tone signal to his handset. As he dials a number, each digit is identified as interrupted line current at the CO. The CO with the help of a panel full of digital circuitry examines whether the line corresponding to the digits dialed by the calling party is free. The line will be found free only when the off-hook switch at the called party's hand set is off. If the line is free, the CO - immediately places a “ringer generator voltage” (50V 20Hz, “On” 2 seconds, “Off” 4 seconds) on the called party’s line as well as part in the calling parties’ line. This timing is different for outer exchange calls. We hear only this ringer sound, being sent from the CO. The timing is different for outer exchange calls.

When the called party at the other end lifts his handset to answer, the off-hook switch in his handset is “on” and only now, his (handset),receiver gets life and making him capable of hearer speak. So the receiver the other end is enabled only when it is lifted there by making the off-hook switch “on”.

As long as the conversation between two subscribers being established, it is the CO which communicates with the calling party just as sending.

 

 Rice contains starch, a polysaccharide made of amylose and branched amylose amylopectin. In rice, it takes the form of granules which are clustered together to form compound grains. The dried starch granules when soaked in water swell and continue to do so when temperatures are is raised. Above a certain temperature the swelling becomes irreversible and the starch is gelatinized.

Lower the amylose content of starch, greater is its swelling. As rice starch has comparatively low amylose, it swells to a large extent on heating. This boiled rice when crushed becomes a paste which can be used as an adhesive.