My Science School

               In modern cities or towns we sometime see moving metal stairs operating in big high raised buildings or shops. They carry people up and down to different storeys. We call them escalators. People use them to avoid physical strains in climbing or descending stairs in such buildings. This moving staircase is also used for transportation of passengers in subways and other mass pedestrian areas in most modern cities. Do you know how does these mechanical stairs work?

               The basic mechanism of an escalator was first invented by Jess W. Reno of USA in 1881. It was used mainly for riding on masts of wooden or iron poles in ships to fasten ropes or belts in order to support a ship’s sails.

               The name “escalator” was applied to a moving stair-way in 1900 and was first shown in an exhibition held in Paris. Originally, the patent was with a company named “Otis Elevator Company”. Subsequently the word “Escalator” became popular through its use by public.

               Modern escalators are normally limited in size to about 60 feet (18 metres). Its floor to floor rise is about 12 feet (5 metres) apart. They are electrically powered and driven by an endless chain that goes round and round without stopping. A motor drives the chain connecting the steps together. At the end, its steps go underneath the escalator and back to the beginning. The steps of an escalator run on rails below the steps arranged beside each other so that the steps are raised one above or below the other like that of a staircase. Near the top and bottom, the steps level out in such a way that the users can walk on or off the escalator easily.

               An escalator generally rises at a rate of upto 120 feet (36 metres) per minute. Very large escalators have a capacity of 6,00C passengers per hour to transport.

               If a chain breaks or displaced somehow, the release of tension stops the escalator. Moreover, a safety switch in an escalator is so designed, that it halts the escalator immediately if the escalator develops some defects or disorders. 

               Sugar making process was known in India as early as 3000 B.C. In Sanskrit, the word sugar is Sakkara. Gaura, another old Indian word for sugar was derived from the name of Gur for domestic non-purified sugar.

               Do you know how is sugar made by modern techniques? Before that it is worthwhile to know how sugarcanes and beets were first used to make sugar. Sugarcane is believed to have originated in Solomon Islands in South Pacific. The methods of sugarcane growing were passed from India to Indochina (modern Vietnam and Cambodia) and from Arabian countries to Europe. It is said that in 1493, Columbus brought sugarcane to the New World. Similarly beet grew wild in parts of Asia and also cultivated quite early in some part of Europe. In 1747, Andreas Marggraf, a German chemist proved that beet-roots contained sugar that can be extracted in crystalline form to make sugar. 

 

 

Continue reading "How is sugar made? "

               A video telephone is a communication device used for simultaneous exchange of visual images and the associated speech. In this system one can see the face of the man talking at the other end and can also listen to his voice. Do you know how this telephone works?

A complete video telephone system consists of the following parts.

1. A terminal equipment which has a camera, display screen, microphone and a speaker phone. These instruments transform both voice and visual inputs into electrical signals and vice versa.


2. Transmission facilities which carry the electrical signals upto long distances.


3. A switching system to allow a choice of terminals to be interconnected. At the transmission point, voice and picture both are converted into electrical signals which are carried to a long distance through transmission arrangements. At the receiver end these signals are converted into voice and picture which can be heard and seen by the person sitting at the receiver end.

               Video telephone system was developed in 1927 by H.E. Ives who transmitted one way images by wire from Washington DC to New York. In the same year images were also transmitted from New Jersey to New York by radio also. These experiments were aimed at transmitting and reproducing a recognizable human face. In 1930 Ives demonstrated a two-way video telephone over a wire path in New York City. From 1936 to 1940 a public video telephone service was provided on a local and intercity basis by the German post offices. Calls could be set up by appointment between any two subscribers in Berlin, Leipzig, Nuremberg and Munich. A similar system was inaugurated by the Soviets in 1961 for subscribers in eight cities, including Moscow, Kiev and Leningrad.

               Since the 1960s most major communication agencies throughout the world have been exploring the feasibility of a commercial video telephone service. The first limited commercial video telephone service was offered in the early 1970s by the Bell system. In this system ordinary telephone wires utilizing specially designed repeaters were used to transmit the video signals. Video requires two pairs of wires, one for each direction of transmission. This early service between Chicago and Pittsburg provided valuable insight into customer needs, but customer acceptance did not meet the early expectation.

               Nowadays researchers are also experimenting in the field of video telephone systems, using communication satellite links. In many developed countries the system has now become popular after vast improvement of its mechanism in terms of perfection at the level of customer’s expectation. 

          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.

 

Scientists have developed techniques through which gases like nitrogen, oxygen, hydrogen, and helium can be converted into liquids. These techniques involve cooling of the gas to a certain temperature called the critical temperature and then it is compressed to a very high pressure. Due to this cooling and compression the molecules of the gas come closer and the gas gets converted into a liquid. Air is a mixture of nitrogen, oxygen and other gases and can be liquefied by cooling it to about -200°C at normal atmospheric pressure. Under high pressure it can be liquefied at about -141°C.

The technique used for the liquefaction of air is shown above. Through this technique the air from the atmosphere is compressed to a high pressure. This air is then allowed to expand rapidly. As a result, the air gets cooled to a very low temperature. Its heat is lost due to the sudden expansion. This cool air is compressed further by which it gets converted into liquid.

Liquid air is very cool. It is a mixture of liquid oxygen which boils at -183 °C, liquid nitrogen which boils at -196°C and liquid argon which boils at -186 °C. It is bluish in colour and is kept in special vacuum flasks. It is mainly used in research laboratories to produce low temperatures.

Liquid hydrogen boils at -253°C. It is cooler than liquid air. Liquid helium is still cooler. It boils at -269°C. All the liquid gases should be handled with care. If they fall on your skin they may damage the body cells. If a rubber tube is inserted in liquid air it becomes as hard as a wooden stick. 

           Ordinary water does not remove dirt from things because grease and water do not mix. So soap is one of the most common cleansing agents used all over the world. People use soaps and detergents to clean their skin, clothes, utensils and many other objects. How does soap remove dirt?

          Soap is basically a fatty acid salt which can be obtained by boiling fats or oils together with an alkali. When oil is allowed to react with caustic soda solution, the chemical reaction produces soap and glycerin. Both are separated. When soap is applied on a cloth, its molecules break into fatty acid ions and sodium ions. Fatty acid ions are repelled by water but are attracted towards greasy dirt particles. They surround each grease molecule and remove it from the surface of the cloth. These are carried away by the water and consequently the cloth gets cleaned. Other actions, such as agitating, squeezing or rubbing and rinsing help loosen dirt and grease so that water may carry them away.

          Today, chemical cleaners called detergents are more and more in use instead of ordinary soaps. Detergents clean better than soaps in hard water, (the ‘hardness’ of the water is caused by the presence of calcium and magnesium salts. Soap does not make much lather in hard water) but they do not, by themselves, make suds. Suds are not necessary for cleaning but substances that make suds are added to detergents.

          Many substances are added to a crude soap to make it suitable for use as toilet soap. Coconut oil is added to make it lather quickly. Dyes, perfumes, water softeners and germicides, which are tiny substances that kill germs, are also added. 

               Optical microscopes cannot magnify more than about 2500 times because the light rays can not produce a sharp image. The electron microscope is such a powerful instrument which can magnify minute objects by as much as a million times. It is used to study micro-organisms such as viruses, tissues and bacteria. We know that light travels in the form of waves. Similarly, waves are also associated with the moving electrons. These are known as matter waves. Electron microscope was constructed by making use of matter waves associated with electrons. Wavelengths of light waves are longer than that of the waves associated with electrons. Due to this reason an electron microscope has a higher resolving power and greater magnifications as compared to an optical microscope.

               The electron microscope works like an optical microscope with a condenser and objective and eyepiece (projector) lenses. The lenses are powerful magnets or electrodes.

               In an electron microscope a beam of electrons is focussed onto the object. With the help of electromagnetic lenses an enlarged image of the object is produced on a fluorescent screen. This image is photographed on a photographic film or plate. With the help of this photograph the object structure is studied in detail. Most of the big research laboratories make use of electron microscopes.

 

 

            Photostat or xerography is a means of copying documents, letters or pages of books without using liquid inks. This could be called ‘dry writing’.

            A photostat machine makes use of static electricity. It relies upon the special properties of an element called selenium. When the light falls on selenium’s surface its electrical resistance drops sharply.

            To copy a page, the operator places it face down, upon a horizontal glass window. The button is pressed on the photocopier and a bright light comes on to light up the page. Its image is projected onto a highly polished selenium-coated cylindrical drum through a lens. The drum is charged with static electricity.

            The place where the light reflected from the white parts of the page falls on the selenium drum, the electrical resistance of the drum drops. Selenium’s charge leaks away to the ground. The light does not reach the drum from the black areas of the page. The drum on these areas retains the electrostatic charge. Now the drum is covered with a special powdered black ink. The ink adheres to the drum where there is still an electrostatic charge and so the image of the document gets formed in powdered ink on the selenium drum.

             Now a sheet of plain white paper is pressed close to the drum. The paper develops a charge opposite to that of the drum by induction. This charge attracts the ink powder from the drum. The ink jumps from the selenium drum to the paper, thus transferring the image to the paper. The paper is heated before it leaves the machine. This melts the ink which sticks permanently to the paper, giving a reproduction of the original document.

            In another type of electrostatic copiers, the image of the page is projected directly on to the paper, which charges its surface. The paper then passes through a bath of toner and the particles cling to the charged parts of the paper to produce the copy.

 

           Solar energy comes from the Sun to the Earth in the form of light and heat. It can be converted into electricity by solar cells. Today, scientists are engaged in developing new techniques for the benefit of mankind.

           Experiments have shown that when sunlight falls on certain metals like potassium and silicon, electrons are emitted from their surfaces. These electrons are known as photoelectrons and this phenomenon is called photoelectric effect. Photoelectrons so emitted can be used to produce electric current.

           Photoelectric effect has been used for the making of solar cells. A solar cell, in fact, is a device that directly converts solar energy into electric energy. These wafers of silicon element are used for making solar cells. Generally, a four centimetre long and two centimetre broad and 0.14 millimetre thick silicon wafer is used for one solar cell. When sunlight falls on this wafer it gets converted into electric energy. Each solar cell is capable of producing about a half volt of electricity.

           To produce useful quantities of electric current, it is necessary to join together a great number of solar cells. The cells are joined together in big panels and are placed in the sunlight. A panel of about 20,000 solar cells can produce 500 watts of electric power. The electricity produced thus can be used either immediately or can be used to charge electric storage batteries for later use. Materials like cadmium sulphide and gallium arsenide are also being used for making solar cells.

           Solar cells have several different uses. In sunny places, solar panels are used to provide boost power to telephone signals. In space where the supply of solar energy is plenty, solar cells are particularly useful. Spacecrafts, space-laboratories and satellites have a number of solar panels to provide power for their equipments.

          The biggest solar energy furnace of the world is in California, USA. It uses almost 2000 mirrors, which focus the sun rays on to a boiler unit on top of a tower. This produces steam which is used to drive electricity generating turbines. In India, The Bharat Heavy Electricals Ltd. (BHEL) and Central Electronics Ltd. (CEL) are making cells that have found many applications.

 

A camera is the instrument that will give us picture of a person or a scene called a photograph that can be kept for sweet memory. It has become one of the most important means of communication and expression in modern times. Basically, a camera is a dark box fitted with a lens on one side. Just behind the lens there is an aperture which controls the amount of light admitted. A shutter exposes the film to the light for a short interval. A photosensitive film is mounted on the opposite side of the lens. This film has a layer of silver bromide coated on it.

The object, whose photograph is to be taken, is focused on the film. This is done with the help of another lens called a view–finder. On opening the shutter the light from the object enters the box through the lens. An inverted image of the object is recorded on the photo film.

The exposed film is taken out of the camera and developed by a chemical process. For developing the film a solution of quinol and metal is used. During this process the portion on which more light has fallen becomes darker and the image of the object appears in reverse tones. The developed film is put in the hypo solution for fixing the image. That is how the negative of the object is obtained. In the negative white portions appear dark and black portions appear white.

Now with the help of an enlarger, a print or positive is made from the negative. The light coming through the negative is focused on the photosensitive bromide paper. This paper, after developing and fixing, takes the shape of a positive. That is how we get the photograph of an object.

There are a lot of developments taking place in the field of photography. Nowadays, the techniques of making coloured photographs are being used on a large scale. Instant cameras take photographs in a few seconds. These instant cameras are called Polaroid cameras. Some special cameras produce motion pictures like TV and video cameras, the pictures are made electrically. Holography has given birth to three dimensional photography in which we can see the length, breadth and thickness of the object.

          We make use of dry cells in our torches, transistors and cameras. As soon as we press the switch of the torch the filament of the bulb gets heated up and it begins to glow. Similarly, when we switch on our transistors sound is produced. These devices get their energy through the electric current produced by the dry cells fitted in them. There are three main types of dry cells: carbon-zinc, alkaline and mercury.

          A carbon-zinc dry cell consists of a cylindrical vessel made of zinc. A carbon rod with a brass cap is placed at the centre of this vessel. Zinc acts as the negative electrode and carbon as the positive electrode. A paste of ammonium chloride, zinc chloride, manganese dioxide and carbon is filled in the vessel around the carbon rod. The paste is further surrounded by another paste of plaster of Paris, ammonium chloride and zinc chloride. Plaster of Paris makes the paste hard. The zinc vessel is closed with a layer of pitch. Finally, the vessel is wrapped with a thin cardboard and we have a carbon-zinc dry cell. This cell is a lechlanche type of primary cell in which the electrolyte ammonium chloride is dissociated into positive and negative ions. These are attracted towards the electrodes and produce voltage. When they are connected with a wire, current begins to flow. In this reaction hydrogen gas is also produced and it is converted into water by manganese dioxide. These cells produce electricity till the whole of the manganese dioxide is used up to convert hydrogen into water. Manganese dioxide, after the reaction with hydrogen, gets converted into manganese oxide. After this conversion, no electricity is produced by the cell.

          An alkaline dry cell battery is more powerful and lasts eight times more than a carbon-zinc cell. It also has a carbon electrode and a zinc casing electrode. The electrolyte is a strong alkali solution which has potassium hydroxide. Alkaline dry cells are used mainly for portable radios.

          In a mercury dry cell, the voltage remains constant till the end of the life of the battery. A mercuric oxide electrode is used. The other electrode is the zinc casing. The electrolyte is potassium hydroxide.

          Why these cells are called dry cells? It is simply because its electrolyte is not in a solution form but in a paste form. It would become useless the moment the electrolyte dries up. Dry cells are adversely affected by high temperatures. Hence they should be stored in a cool place, away from direct sunlight. It is better to take out the cells from the torchlight, camera or transistor if they are not being used because moisture leaks out from the cell and it swells up. 

An airconditioner is an electrically operated device used to keep houses, offices, and laboratories cool during summer and warm during winter. It not only controls temperature but also regulates humidity.

Today, airconditioners of all types and sizes are available. The big airconditioner plants are capable of cooling or heating an entire building.

          In general, an airconditioner keeps the temperature between 20°C and 25.5°C and relative humidity around 35-70%. An airconditioner plant consists of a compressor and a cooling liquid like the Freon gas. The cooling liquid evaporates in the cooling coil. This vapour is then carried to the electrically-operated compressor. It then goes to the condenser where it is cooled by air or water as it passes through the radiator. Here the vapour changes to a liquid giving off heat in the process. The compressor thus serves to transfer heat from one place to another. A fan sends fresh air into the room which keeps the temperature of the room to the desired level. The airconditioner has certain substances which remove the moisture from the room. It also has filters to remove the dust particles from the air. This is how an airconditioner controls the temperature and humidity and keeps the air clean. Some airconditioners have attachments so when turned on we get hot air in the winters.

          Many new buildings, factories and homes are now being designed to include air-conditioning. Ships, aeroplanes, cars, offices, restaurants, theatres, shops and space vehicles make use of this steady flow of comfortable, purified air.

 

          A refrigerator is a cabinet used for keeping food and other substances cool and fresh. It has solved the problem of storing food for short periods, particularly in hot climates. The freezing compartment can store foods for months together.

          The working principle of a domestic refrigerator is shown in the figure. It is a compression and absorption refrigerator. Compression-and-absorption systems cool by changing a refrigerant from a liquid state to a gaseous state and back into the liquid state again.

          It consists of a storage tank, filled with Freon gas, the refrigerant control device, the evaporator, the compressor and the condenser. When the machine is switched on, Freon gas leaves the storage tank under high pressure. It travels through pipes of the refrigerant control device. These pipes act as evaporator. The liquid Freon absorbs heat from the pipes and gets evaporated. As the heat is drawn out, the temperature inside the cabinet and that of the food materials falls. Freon gas is now again converted into liquid by the condenser and the compressor. This cycle continues and the temperature inside the cabinet goes on falling. When the temperature inside the cabinet reaches an optimum value, a thermostat control cuts off the electric power and the machine stops. Again the temperature starts rising. When it reaches a certain mark, thermostat control again starts the machine. In this way a constant temperature is maintained and the food materials are preserved.

          Home refrigerators are sealed, airtight, leak proof, heavily insulated cabinets that maintain cooling temperatures between 0 and 4°C. Most of them have freezing compartments that can maintain temperatures between -18°C and -14°C. Either electricity or gas may be used to power refrigerators. 

          A vacuum cleaner is an electrically operated machine which is used to clean carpets, rooms, floors, book shelves and electronic instruments. It can conveniently remove dust and bits of paper. It can be handled by a single person and has proved very useful in cleaning homes, factories, stores, curtains, carpets, walls and cars.

          The inventors of household appliances in the late 1800s sometimes succeeded by trial and error method. The first electric cleaners actually blew out a stream of air to dislodge dust from carpets. Unfortunately dust went and settled down on everything else! In 1901 an inventor named H.C. Both had another idea. Why not make the cleaner suck and not blow? To see if the idea worked, he lay down on the floor and began sucking through a handkerchief. It worked, and H.C. Both built the first modern vacuum cleaner.

          A vacuum cleaner consists of a small electric motor to which a small fan is attached. The fan rotates at a very high speed. It sucks the dust in from one side and throws it out from the other. A cloth bag is fitted in the machine to collect the dirt. This bag is made in such a way that it allows the air to push through while even very tiny dust particles are trapped in. When the cleaner is turned on, the fan inside spins very fast. And as the cleaner’s nozzle is pushed along on the carpet, air rushes in taking the dust and dirt from the carpet along. These get trapped in the cloth bag and the carpet becomes clean.

          In fact, when the fan rotates, a partial vacuum is created inside the machine. That is why it is called a vacuum cleaner. Because of the partial vacuum, the pressure of the outside air pushes dust and small light-weight materials into the bag.

          Modern industrial vacuum cleaners are able to suck up rubbish including wood shavings, broken glass and even liquid. 

             Video games are played either on home television or computer display screen or used for commercial purpose in amusement shops (arcades). Most video games are meant for entertainment but some are meant for educational purposes too. They may be played by one person or in competition with others.

              Most video games present changing colourful visual effects and complicated sound effects. A video game is controlled by a microprocessor. All video games have a programme. They are connected to a viewing screen or video screen that is why these games are called video games.

              Video games are of two types, namely, arcade games and home games. Arcade games are designed to play one kind of game while home games are programmable, i.e. they can be programmed to play different kinds of games.

              Equipment for a typical video game consists basically of a microprocessor module connected to a television set. A cartridge inserted into the module provides the programme for the games action. The cartridge contains a ROM chip. This chip has all the instructions for playing the game and its accompanying sound. The action circuit board connects the ROM to the game console. A key board, key pad, rotary knob or joy stick control the action. A home computer can also be used for playing these games.

              Video games are modelled on war themes or space travel. Some are sports card games, board games and word games.

               Video games are a favourite of children of all age groups as well as adults.