My Science School

            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. 

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.

 

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.

         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.

 

           A hot iron smooths out creases in cloth. Most irons are powered by electricity. Inside the iron is an electric heater. A steam iron provides heat and steam at the same time for ironing many different fabrics. Steam makes the cloth slightly damp which helps to remove creases, and wrinkles because moisture softens the fibres in the material and makes them flexible.

          A steam iron contains a water tank in which water is boiled by the heating element to make steam. A push-button on top of the iron opens a valve to let the steam through the holes on the cloth being ironed. With the button up, no steam gets through to the cloth and the iron works like an ordinary iron.

 

          The remote control is a small hand-held device used by a viewer to control the television without touching its controls. It is an opto-electronic device which makes use of optical and electronic techniques and hardware.

           The remote control device emits a beam of light which is detected by a, “light control” built into the television. In an optical remote controller, a multivator (1) produces pulses (2) from push button controls (3). The pulses are amplified (4) and modulate a beam of light in the form of saw tooth pulses (5) These pulses are received by a photo transistor (6) fitted in the television set, amplified (7) and used as a trigger to recreate the pulse shape (8) The resulting signals are used to change volume and channels.

          The volume, contrast and channel can be altered by remote control. If the television is connected to a video cassette recorder, programmes can be recorded and replayed by remote control. A remote control prevents the wear and tear of switch buttons. 

              Scientists have developed the devices by which a door can be opened or closed automatically. There are three common ways of operating automatic doors: (1) by actuating a pressure pad on the surface in front of the door, (2) by cutting a light beam located in a wall near the door and (3) by actuating a wall mounted manual pressure pad like a switch.

              Automatic doors are powered by various drive systems - some are totally electric, some are electromechanical and others are pneumatic. Various door opening actions are available such as automatic slide with or without manual swing out side panels for use when the automatic doors are locked or turned off; single or double swing doors and side and swing combinations. Automatic door opening and closing devices are becoming more and more popular day by day. 

A battery is a device that produces electricity by chemical action. A battery contains one or more units called cells. Each cell can produce current.        

There are three main types of dry cell batteries: carbon-zinc, alkaline and mercury. Here we are describing an alkaline battery.

An alkaline dry cell battery is more powerful than carbon-zinc battery. It lasts five to eight times longer than a carbon-zinc battery. It has carbon and zinc as electrodes. Instead of a carbon rod extending from the top, a nail like collector (1) is inserted from the bottom. The granules of zinc which form the anode (2) are made uniform in size and shape. The electrolyte - a solution of potassium hydroxide - is in direct contact with the anode, ensuring that the anode is exhausted by the end of the battery’s life. The manganese dioxide cathode (3) is made by electrolysis. The additional oxygen increases the reactivity of the cell. Alkaline dry cells are used mainly for portable radios. 

                  Rubber, which is in common use, is of two types, namely, natural rubber and synthetic rubber. Natural rubber comes from the juice of a tree while synthetic rubber is made from chemicals.

                 Synthetic rubber was first developed before 1900 from the hydrocarbon isoprene which was synthesized from turpentine. Almost all types of synthetic rubber are obtained from petroleum industry. Important sources are styrene, acetylene and butadiene. Two of the most important types of synthetic rubber are butyl rubber and styrene-butadiene rubber. These two rubbers along with natural rubber made up about 90 percent of the worlds’ demand.

                Natural-synthetic rubber is also an important rubber for the industry. These are the synthetics that duplicate the molecular structure of natural rubber and can be used interchangeably with the natural product. Since World War II, a lot of products such as foam rubber have been directly made from natural rubber latex or from synthetic equipment.

 

Continue reading "How is synthetic rubber made? "

          Skyscrapers are tall buildings that tower in the air. The foundations of a skyscraper are laid by drilling holes in the ground and filling them with concrete. If the ground is firm, the foundations are wide so that they will spread the weight of the building and they do not go very deep. If the ground is not very firm, deep shafts of concrete are driven into the ground to anchor the skyscraper firmly.

          Then a frame of steel griders or concrete beams is erected, often with a pillar like concrete core containing lift shafts and stairs. The frame and core take all the weight of the building so that the walls do not have to support the floors above.

          The tallest skyscraper of the world is the Sears Tower of Chicago state (Illinois) with 110 storeys rising 443 meters. The other famous skyscraper is National Westminster Tower of Great Britain.

           Cellular telephone or radio telephone is a type of mobile telephone which is integrated with existing telephone systems, allowing mobile users to contact any one with a standard telephone and vice-versa. Each mobile telephone has its own number which can be dialed from any other telephone. The cellular telephone can cover the entire country; even inter-continental telephone calls are possible with cellular telephone.

           A cellular telephone network is setup by dividing the country into a series of cells, each with its own radio transmitter controlled by a central switching computer. Each cell is about 5km across and it broadcasts and receives low power signals on its own set of frequencies. Since each cell is so small, the same set of frequencies can be reused in any other cell whose transmitter’s range does not overlap the first cell. As a cellular telephone is mobile and moves from one cell to another, the broadcast frequency needs to be changed.

            Cellular radio phone signals follow a route starting from the mobile, then of the radio transmitter. The signal is sent along the conventional telephone lines to an exchange. The analog signal is converted to digital signal, ready for switching to the correct destination. After switching, the signal is reconverted to analog and sent along telephone lines to the destination transmitter, where it is transmitted and consequently received by another mobile.

           There are at present three types of cellular telephones. These are - automobile based, pocket or briefcase portables and trans-portables which can be moved in a vehicle and used in the hand.

           Cellular phones are being used by many countries besides India such as Saudi Arabia, U.S.A., Sweden, Britain, Japan, Middle East countries etc. 

          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.