My Science School

Zip fastener is a fastening device in which two rows of teeth and sockets are brought together so that they interlock. Metal zips have lines of tiny teeth, while plastic zips contain small loops on each side. When you pull the slide of the zip fastener up, it pushes the teeth or loop together. The first zip was invented by Whitcomb Judson in 1893.

Beneath each tooth in a metal zip fastener is a small socket. The slide is narrow at the bottom so that it forces the teeth together as the zip is pulled up. The teeth on one side fit between the teeth on the other side. As they come together, each tooth slips into the socket under the tooth above and the zip stays closed. As the slide moves down, a divider at the top of the slide pulls the teeth apart.

 

 

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            Electric typewriters are increasingly replacing the mechanical typewriters. The first commercial typewriter was produced in 1874 by Christopher Latham Sholes. It was produced by Remington Company of USA. The first electric typewriter was marketed in the mid 1930s.

            An electric typewriter along with its functional diagram is shown in the figures. An electric typewriter involved less manual labour as compared to the old mechanical machines. The mechanism of this typewriter is more efficient.

            When a key (1) is pressed, a cam (2) makes contact with a drive roller (3) powered by an electric motor (4) The cam is propelled upwards with an even force, causing the cam lever (5) to move back. This makes the upwards movement of the appropriate type bar. (6) The paper is wound on a cylinder which moves along one character at a time during typing. A typing ribbon is forced against the paper by the metal bar, so printing a letter on the paper. As the type bar falls back, the carriage moves one character space to the left. The force of the typing strokes does not depend on the pressure applied by the typist so the results are more even. At the end of a line the typist presses a key that shifts the carriage to the right and at the same time rotates the cylinder, carrying the paper to the beginning of the next line.

            Electronic typewriters are move sophisticated than electric typewriters. Based on microchip control they are usually very quiet to use and their action is faster since they contain less moving parts. They offer more functions especially they have memory that allows user to make corrections.

           The word processor while retaining the advantages of the electronic typewriter keyboard has replaced the movement of the carriage and cylinder by the movement of a cursor on the screen. This means that mistakes can be erased and passages added, removed or repositioned before the matter is typed on the paper. 

               Aerosols were patented in the United States of America in 1914 and have been increasingly used since the early 1950s. Aerosol cans and bottles are used to spray paints, perfumes, deodorants, furniture polish, oven cleaner, pesticides and many other liquid products.

       Initially the can is filled with the product to be sprayed and the propellant. When the push button is pressed, the product is forced up the dip tube and comes out as spray from the hole in the top. The top hole is very narrow and causes the liquid to break up into a fine, mist-like spray. Inside the can, the propellant is a gas under pressure usually a chlorofluorocarbon which forces the liquid in the tube to the top. However, concern about the damaging effects that chloro-fluro carbons have on the earth’s ozone layer has forced scientists to look for alternatives. The top of the can contains a valve with a spring that closes the value when the top is released.

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               The word ‘radar’ is an acronym for ‘radio detection and ranging’. It is, in fact, an electronic device by which one can detect and measure an invisible flying object’s distance and speed. It can work efficiently under all weather conditions such as fog, mist, smoke, snow-fall, storm, cyclone, rains etc. Due to these reasons it is used in the control-room for the guidance of aeroplanes.

              The radar works on the principle of ‘echo’. The sound waves reflected by some obstacle produce an echo. Similarly, radio waves which are electromagnetic in nature also get reflected when they encounter some obstacle in their path. This property of radio waves was discovered by scientists in 1930. Using this property, in 1935 five radar centres was established in America. Major developments in the field of radars took place during the Second World War. These rendered a great help in detecting the enemy bombers. Since then, many kinds of radar have been developed for peaceful uses also. Now, there are radars which help in controlling and guiding the path of unmanned space crafts. Radars giving information relating to weather are also available. 

              Do you know how radar works? Radars make use of radio-waves, similar to those used in radio broadcasting. However, the radio-waves used in radar have higher frequencies. They are called micro-waves. The speed of these waves is equal to that of light i.e. (186000 miles) per second. The radar centre has a transmitter which sends out radio waves with the help of an antenna towards the object. It also has a receiver which receives the radio waves reflected by the object. This receiver has a screen which shows the object’s position in the sky.

             The time taken by the radio-waves in going from the transmitter to the object and in coming back to the receiver is recorded by radar. By multiplying this time with the velocity of light we get twice the distance between the radar and the object. This is how the distance of the object is determined. The radar has automatic instruments which perform all these functions. Initially, radars used to be very big in size, but now there are ones which are even smaller than our palms. 

          Atom bomb is a nuclear weapon which makes a huge explosion powerful enough to destroy a city. It is based on uncontrolled fission chain reaction. When the nucleus of a heavy element like uranium is bombarded by a neutron, it breaks into two large fragments and either two or three fresh neutrons are produced. These neutrons further collide with other nuclei causing more fissions. In this process large amount of energy is released. If the chain reaction continues, tremendous, devastating explosion will take place. This is what we call as atomic explosion.

          To make an atom bomb critical mass of uranium - 235 or plutonium - 239 undergoes fission chain reaction by stray neutrons. In this process tremendous energy is released.

          Based on fission chain reaction, the first atomic bomb was developed during the Second World War by a team of American scientists. The first atomic bomb made of uranium - 235 was dropped on August 6, 1945 on Hiroshima and three days later the second bomb based on plutonium was dropped on Nagasaki (Japan). Those have been most tragic events in the history of mankind. Destruction caused by these bombs ended Second World War.

          After this Russia, Britain, China and France also tested their atom bombs.

 

                   Today, the word ‘rocket’ is used in many forms. Missiles used in wars are also a form of rockets. The space-ships used to collect information about planets and their satellites are also called rockets. We hear of rockets in fire-works also. Whatever be the context in which the word rocket is used, one thing is certain that all the rockets function on the same principle. A rocket works according to the Newton’s third law of motion. According to this law, ‘to every action there is an equal and opposite reaction’. The gases formed by the burning of fuels inside the rocket chamber come out of the nozzle and produce a great force. As a reaction to this, the rocket gets the necessary push to move forward. Do you know how the rocket was developed?

              The story of the development of the rocket starts with China. It was not invented by any single scientist. Its development took a very long time. In the year 1232, the Chinese used the arrows of flying fire in the wars against the Mongols. These arrows were also a kind of rockets. By 1275, rockets came to be in use in India, England, Arabian countries, Germany and France etc. During the early 1800s, Colonel William Congreve of the British Army developed rockets which were used in every war thereafter. In 1926 Robert H. Goddard of America developed liquid propelled rockets. Goddard today is known as “The Father of Modern Rocketry”.

               High speed rockets were developed for space explorations. The space Age began on October 4, 1957 when Russia launched the first satellite, Sputnik I. Today we have solid and liquid propellant rockets, electric and nuclear rockets. For space applications, scientists are using multistage rockets.

 

 

                The submarine is a vessel which is closed from all sides and is capable of easily floating both on the surface of water and under water. It can go very deep into the sea.

                Since long, man has made efforts to reach the bottom of the seas in search of diamonds and pearls. In order to succeed in his attempts he tried to invent some device which could go under water. Thus, first submarine - the boat capable of travelling under water - was devised by Carnelius Van Drebbele of Holland in 1620. This submarine was made up of wood and was wrapped in leather. This could go up to the depth of 3 to 4 metres into the sea water. Thereafter, efforts were made to develop other types of submarines. Up to the end of eighteenth century, various types of submarines were made. Till 1727, fourteen different types of submarines had been made in England alone. 

                 In 1880, a submarine propelled by the steam engine was developed. Later on submarines powered by gasoline and electricity came into operation. Submarines were successfully used in First World War (1914-18). And during the Second World War (1939-45), submarines powered by diesel were also used in sea warfare. Now even nuclear powered submarines have been developed. Modern submarines are made from steel sheets. They are equipped with instruments like periscopes, sonars and radars. The periscopes enable seamen to keep an eye on the situation at the water’s surface. Sonars help in locating the other submarines and torpedoes. There are also arrangements in submarines for breathing. Nuclear submarines have no problem of smoke and gas generated by fuels.

                These days’ submarines are being used for various purposes. They are very useful in oceanography. Missiles and torpedoes are launched from them to destroy the enemy ships. Modern submarines can also attack and destroy the enemy’s submarines. Every submarine has arrangements that help its crew to escape to safety in case of danger. 

              In 1911, Heike Kamerlingh Onnes, a Dutch Physicist, invented the phenomenon of superconductivity. He observed that at liquid helium temperature (4.2K) the resistance of mercury totally disappeared. He called this dramatic decrease in resistance as the phenomenon of superconductivity. It was also observed that near absolute zero, several other metals suddenly show near zero electrical resistance. For this outstanding discovery Kamerlingh Onnes was awarded the Nobel prize of Physics in 1913.

            The theory of superconductivity was devised in 1957 by J. Bardeen, L.N. Cooper and J.R. Schrieffer. This is known as BCS theory.

                  For the last 45 years, scientists all over the world are busy in searching superconducting materials for room temperature use. Niobium-tin alloy is one material which shows super conduction at 18K. Niobium-germanium is a superconductor at 23K. In 1986, L.X. Mueller developed lanthanum-barium which is superconductor at 35K. In 1987, Ching Wu Chu developed Yttrium barium and copper with a transition temperature of 94K. In India many research laboratories such as NPL, TIFR, Saha Institute of Nuclear Physics etc. are carrying out research in the field of superconductivity.

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             The telephone is a device by which we can talk to our friends and relatives living in other cities or countries even. It is being used everywhere, in business, offices, homes and factories.

              The world ‘telephone’ has been derived from the Greek words ‘tele’ meaning far and ‘phone’ meaning sound. Thus, the word ‘telephone’ means the device which takes the sound to faraway places. The story of its invention is very interesting. It goes back to June 2, 1875, when Alexander Graham Bell was working along with his assistant Thomas Watson on some problem related to telegraphy. Bell was on the telegraphic receiver in one room, whereas his assistant was in another room. Watson created some vibrations on an iron strip. Bell rushed to the other room and found that the iron strip vibrating between the poles of a magnet was producing electric current in the connecting wire. It was this historic observation which led to the birth of telephone. He was able to demonstrate the telephonic conversation on March 10, 1876.

                Do you know how the telephone works? It has two main parts: the mouthpiece and the earpiece. The mouthpiece of the telephone works as a transmitter whereas the earpiece works as a receiver. Both are enclosed in one cage and are connected by the line wire. When we speak into the mouthpiece, a diaphragm attached to it starts vibrating. And in accordance to these vibrations a varying current is produced. This current is carried by the telephone line wire to the receiver of another telephone. This varying current produces vibrations in the diaphragm attached to the receiver which is then converted into original sound waves. The person at the other end hears clearly the voice of the speaker. The same process is repeated between our receiver and the mouthpiece of the telephone at the other end. In this way two persons can talk to each other on the telephone.

              Today, every country has a vast network of telephone lines. Thus world has become very small. Thanks to the telephones!

 

              A transistor is a tiny solid state device used to control and amplify an electric signal. Transistors are now used in place of vacuum tubes in many electronic circuits. Transistors are smaller, weigh less, last longer and are less expensive than vacuum tubes. They consume less electricity and produce less heat than vacuum tubes.

             Transistor was first developed in 1948 by three American Physicists, John Bardeen, William Shockley and Walter Brattain. These three won the Nobel Prize for physics in 1956. The development of transistor revolutionized the world of electronics.

                  A transistor is made of a semiconductor such as silicon or germanium with certain amount of impurities doped in them. When impurities of V A group like arsenic or phosphorus are doped in the semiconductor material, it becomes a n-type semiconductor (n-for the negatively-charged electrons). On the other hand, if III A group elements like Aluminium are doped, it becomes a p-type semiconductor (p-for positively-charged holes). 

              Transistors are of two types-junction and field effect. Junction transistors are again of two types npn and pnp. In an npn transistor, the middle layer is p-type while the two outer layers are both n-type. The middle layer is the base, one outside layer is the emitter and the other outside layer is the collector.

              Another type of junction transistor is pnp transistor which contains a layer of n-type semiconductor sand witched between two layers of p-type semiconductor. In the pnp transistor, the positively charged holes move from emitter to collector.

             In a field effect transistor, there are only two layers of semiconductor. The current flowing through one of the layers, the channel, is controlled by a voltage connected to the other layer, the gate.

             Transistors are used in computers, stereos, radios, televisions, satellites and many other electronic circuits.