Category Applied Science and Technology

What is a Compact Disc?

            Compact disc is a new kind of disc which is recorded and played by laser beam. Compact disc has silvery, mirror-like surfaces which reflect light in a rainbow spectrum. The music disc is about 12 cm dia. while video disc is about the size of an LP and hold both pictures and sound.

            In the recording process, sound signals are converted into number so that each part of the signal has a precise code. These numbers are recorded as the binary digits 0 and 1. Physically, sound is recorded on a CD as a series of minute pits and flats which relate to the two digits.

           The laser disc has a very reflective metallic surface, covered by a protective coating of clear plastic. A semiconductor or small He-Ne laser is used for scanning. The player spins the disc and scans with laser beam which moves straight across the disc from the centre to the edge. The shiny surface reflects the beam back into the player, where it is picked up by electronic device. This produces an electrical signal which the player decodes back into video pictures and sounds. The laser beam reads about 20,000 digits every second which are converted into sound signals.

           The biggest advantage of compact discs is that they never wear out because there is no physical contact between the disc and the player – only a beam of light. 

What is the principle of an autopilot?

Most large planes have an autopilot. This is a device operated by a computer. It will fly the plate without the pilot’s touching the controls. These autopilots can even control take offs and landings.








The principle of an automatic pilot is similar to the automatic steering of ships, but here three gyroscopic sensors and their associated equipment are used to control the three variables in aircraft position.

These three variables are yaw, pitch and roll. The complex autopilot system uses an airborne computer which activates servomotors for introducing necessary corrections. A radio or radar link to the computer allows control from the ground for automatic takeoffs and landings.


What is bar code?

A bar code is computerized information encoded in a pattern of black and white stripes. The black and white lines represent IS and OS and can be read by light. They carry encoded information – from the membership number of a sports club to the price and stock number of a packet of washing powder in a supermarket. In fact bar codes are used to store data of all kinds.

The code is scanned by a beam of light. When a beam of light is passed over the bar code only the white stripes reflect back the light. This is picked up by a photo – detector which produces a pulse of electricity when it receives light. So the black and white bar code is translated into on/off pulses of electricity. These pulses are fed into a computer for decoding. Nowadays laser beams are being used for reading the bar codes.

What is LPG?

         The term LPG stands for liquefied petroleum gas. LPG is commonly used for domestic cooking purposes. It is supplied in gas cylinders that need to be replaced when their fuel contents are consumed. The supply in gas cylinders contains a mixture of liquefied butane and iso-butane under pressure. The mixture remains a liquid under pressure but the highly volatile liquid fuel in the cylinder evaporates when pressure is released. The gaseous mixture starts going into the burner of attached stove or oven. Here it is ignited and the blue flame is used for different purposes.

         LPG is used as a cooking fuel. This is also used in water heaters, space heaters and furnaces. This gas is also used to heat incubators and brooders, to sterilize milking utensils and other equipments, dry fruits and vegetables and prevent frost damage.

         Moreover, LPG is highly combustible and forms an explosive mixture with air, therefore, any leakage followed by its mixing with air can cause a severe explosion just by the ignition of one match stick. In order to make gas leakage easily detectable some strong smelling substance is added to LPG. Before igniting the match stick we should be sure that there is no such smell near the gas cylinder or in the kitchen.


What is Plastic Surgery?

              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.


What are different types of telescopes?

            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.

What is Plastic?

            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. 

What are the methods of time measurement?

             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.


What is dry ice?

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.


How do we see clearly with spectacles?

              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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