My Science School

               A water or lift pump, often called a tube well, is used to lift water from a lower level to a higher level. These pumps are used in houses or on roads for boosting up the underground water. They work on the principle that atmospheric pressure can support a vertical column of water upto 9 metres in height.

               In this pump, an iron pipe is put into the ground up to the level of water. On the top of this pipe, another pipe of bigger diameter is fitted. Several components of the pump are fitted into this pipe. It consists of a handle which is connected to a piston which moves up and down, inside the barrel. It contains two valves, of which one is fitted with the piston and the other at the junction of the two pipes. Both these valves open only in the upward direction.

               When the piston is pulled up with the help of the handle, the pressure in the iron pipe falls. This opens the valve fitted at the junction of the two pipes closing the upper valve. During this action, the pressure above the surface of water becomes less than the atmospheric pressure. This makes the water rise up in the pipe.

               Similarly when the handle is pulled up, the piston goes down and the valve at the joint closes due to the weight of water. Now the compression of water opens the upper valve. This makes the water rise up further. With this repeated action the water level continues to rise until water comes out at the top.

               However, this pump has two limitations. Firstly, water is discharged only on the upward stroke. And, secondly, although in principle, it can lift water upto a height of 9 metres, in practice it is only about 8 metres (or 30 ft) above the water surface.

               The modified version of this pump is called force pump. In this pump, the upper valve is not fitted to the piston but to the opening. With this modification, the water can be pumped to a much higher height. Force pump can raise water from greater depths and is used to send water to the upper floors of multi-storeyed buildings. For the continuous supply, centrifugal pumps are used these days. These usually run on petrol, diesel or electricity.

 

            Lathe is a widely used machine in the workshops. It is primarily used to give a round shape to materials such as wood, metal or plastic. It is also used for cutting screw threads. Do you know how a lathe machine works?

            A modern lathe consists of an electric motor which spins the given material on a horizontal axis. The speed of the motor can be regulated according to the requirements. This motor rotates a chuck. The work piece is mounted on the chuck. When the motor revolves, the chuck also revolves with it. A cutting tool is brought against the spinning material which cuts away the material until the desired shape is formed. The cutting tool is mounted in a special holder and can be moved in several directions — up and down, and from one side to another.

            Lathes also have a sliding tailstock which is used for centering the work piece. By mounting a drill bit with the tailstock it can be used to drill holes into the work piece.

            Lathes are extremely accurate. They can perform shaping and cutting operations, upto an accuracy of .0002 cm. The most widely used type is the centre lathe or engine lathe. Another popular type of lathe is the turret lathe. In the tool holder of this lathe, six cutting tools can be mounted. This makes it possible to bring several different kinds of cutting tools into use without stopping the machine. Moreover, once the cutting tools have been set, the same operations can be done on piece after piece. When thousands of such operations are needed, a multiple spindle bar machine is used. It is a kind of lathe that performs six different operations. A single computer can run many lathes in large automated factories. A person mounts the work pieces in the lathes and removes them when work is over. Until 1800, lathes were crude machines which could perform a few basic operations only. Around 1800, Henry Maud slay of England, invented the first thread cutting machine. In 1873, C.M. Spencer of USA developed the first fully automatic lathe. By the end of 1900s, a form of automation called numerical control was used to run many lathes at the same time.

 

            We know that electricity is generated at power stations through large generators. Normally power stations are of two types: hydraulic and thermal. These power stations are at a distance from cities to avoid pollution. Electricity is transmitted to the cities and villages with the help of the transmission lines. Do you know how it is done?

            Electricity is transmitted with the help of two parallel wires. In modern power stations the voltage increases as much as 400,000 volts. The reason is that the power lines which carry the electricity lose power if it travels of low voltage and therefore, the voltage is increased in a step-up transformer. The current is then fed into a network of high-voltage power lines called “Grid”, which distribute electricity for use through different sub-stations and underground cables or overhead wires. But before it can be used, the voltage is lowered suitably in a stepped down transformer.

            Big factories and industries may consume current of several thousand volts, but for domestic use of current, it may be upto 220 volts. In this way electricity is transmitted from power stations to distant areas.

 

               Two centuries ago there were two conflicting theories of light. These were Corpuscles Theory suggested by Isac Newton (1642-1727) and Wavelength Theory propagated by Christian Huygens (1629-1695). The theory of Huygens was subsequently established by an English physicist Thomas Young (1773-1829). Newton suggested that a beam of light consists of tiny particles (corpuscles). And since light was corpuscles, Newton argued, it travels in straight lines and casts sharp shadows. It also explained as to why mirror-reflected light simply bounced off the glass like tennis balls off a wall. Newton thought it might be caused by the corpuscles that travel faster in glass and water than through air.

               In contrast, Huygens believed that light travelled in waves like ripples on a pond. He also showed that each colour of light has a different wavelength. He proved that light travels slower through glass and water than through air. The amount of refraction, that is, the amount of light is bent depends upon the light. The shorter the wavelength the more is the bending. 

               In 1801, Thomas Young, based on the theory of Huygens, established the wavelength theory beyond doubt. He shone a beam of light through silts in a piece of card. The silts divided the light into two beams which when recombined, formed a pattern of alternate light and dark bands on a screen. He reasoned that the pattern was produced by interference between the waves of two beams.

               Now, what is actually interference of light and how it is defined? According to Huygen’s theory, light waves spread out from their source in ever increasing circles. It tells us that where two light waves meet, they combine in some places on their way and cancel out each other. This process is called “interference of light”. When two wave-lengths of light met they reinforced each other and produced a bright band. On the other hand, where one crest (higher part of the wavelength of light) met another they cancel each other to form a dark shade.

               It is interesting to note that for more than a century, Newton’s theory seemed more popular because of his name and fame. This position was changed when Thomas Young convincingly proved and established the wavelength theory of light. His experiment on “interference” was important among other experiments conducted by him in this connection.

               Today, modern physicists explain the optical phenomena of light in terms of waves, e.g. interference, refraction, reflection, or diffraction.  

               A battery is a device that produces electricity by chemical action. It contains more than one cell. Each cell produces its own current. Batteries with several cells are used to provide electricity for automobiles, heavy equipments, space crafts, submarines and emergency electric lights.

               The battery which is used in a car is called a storage or wet battery. Storage or wet battery like car battery has a greater capacity and produce more electricity in comparison to other batteries. It can be recharged again and again in order to use for a considerably longer period. The first such battery was invented in 1859 by a French physicist, Gaston Plante.

               Storage or accumulator batteries are of two types: acid accumulators and alkali accumulators. Lead-acid batteries consist of plastic or hard-rubber containers. These batteries are used in cars throughout the world. Each cell of this battery contains two sets of electrodes. The pairs are suspended in dilute sulphuric acid. One electrode is positive and the other negative. One electrode is made of spongy lead and the other of lead dioxide. The separator plates keep them apart. This cell requires distilled water. Such a cell has a potential difference of 2 volts and the cells are connected in series. Most car batteries have 6 cells, giving 12 volts in all.

               At the positive electrode, lead dioxide reacts with hydrogen and sulphate ions of sulphuric acid and forms lead sulphate and water. In this reaction, two electrons are obtained from the wires which balance the chemical reaction. At the negative electrode, lead reacts with sulphate ions and forms lead sulphate. This provides two electrons to the wire which maintains electrical balance. The net effect of this reaction is that electrons start flowing from the negative plate to the positive plate.

               When the lead of lead dioxide is over, the cell stops working. This cell can be re-charged by making the electricity flow from the negative to the positive plate. 

               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. 

 

 

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               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.