My Science School

          Radium is one of the few metallic elements that constantly emit invisible radiations. Such elements are called radioactive elements and the radiations they emit are called ‘radioactive’ rays. There are three types of radioactive rays - alpha, beta and gamma rays. Radium, due to the emission of the radioactive rays, disintegrates and finally gets converted into lead. Half of this radioactive element gets converted into lead in 1622 years. This is called the ‘half life’ of radium. In the next 1622 years, half of the remaining substance decays into lead. This process continues indefinitely. The radioactive rays are so powerful that they can pass through different kinds of substances including the human body. These rays are very useful in the treatment of cancer. Do you know who discovered radium?

          Radium was discovered in 1898 by a French married couple, Pierre Curie and Marie Curie. The story of its discovery is very interesting.

          In 1896 Henri Becquerel discovered the phenomenon of radioactivity. He found that the uranium emits a kind of invisible radiations which are more powerful than even the X-rays. In 1898 Pierre Curie and Madam Curie, found that thorium also emits similar radiations. They thought that pitchblende, which is the ore of uranium, must contain some other radioactive substance too. They started refining pitchblende in order to obtain the new radioactive element. They had to work in a tin-shed because they could not afford a proper laboratory on account of limited means. Without caring for rains and storms, they worked day and night. Finally, they succeeded in extracting 100 milligrams of radium from several tons of pitchblende. They found that this new element was much more powerful than uranium.

          Pure radium is white in colour. It is quite heavy and thousands of times costlier than gold. The quantity of pure radium available in the world is very small. Radioactive rays are very harmful to the body. If handled carelessly its radioactive rays can cause bad radiation burns. There are 16 isotopes of radium. The most common is radium 226. It is used in medicine to destroy cancer growths.

 

          Enrico Fermi was a great Italian-American theoretical physicist. He was one of the chief architects of the nuclear physics. He was awarded the Nobel Prize for Physics in 1938 for his outstanding discovery of neutron-induced nuclear reactions.

          Fermi was born in Rome on 29th September 1901. He was a brilliant student and obtained his doctorate in Physics from the University of Pisa at the age of 21. His research was on X-rays.

          In 1926 Fermi became a full time Professor of theoretical physics at the University of Rome. In 1929, he was elected a member of the Italian Academy. In 1934 he succeeded in making a fundamental discovery in the field of physics. This was the result of 10 years of arduous research. He discovered that when elements are bombarded with slow neutrons, the material becomes radioactive and begins to emit radiation. In this process the element changes into a different material. For example, iron, when made artificially radioactive by neutron bombardment, turned into manganese. In this way Fermi found about 80 new artificial nuclei. 

           About this time, Italy, under Mussolini, was in the grip of a Fascist government. This affected Fermi directly because his wife was a Jew. So he wanted to leave Italy. Fortunately at this time (in 1938) he was named for Nobel Prize. He was given permission to go to Sweden to receive the award. Fermi left Italy with his family never to return. After receiving the award, he went to U.S. and became a citizen of United States. Subsequently he became Professor for Nuclear Studies at Columbia University.

            In 1942, during World War II, Fermi built the first atomic reactor in an empty Squash court in Chicago. Here he set off the first man-made nuclear chain reaction. Later he helped to develop the atom bomb.

 

          The invention of wheel has proved to be one of the biggest blessings for the mankind. It is used in almost all modes of transportation: trains, buses, trucks, cars, aeroplanes, scooters, cycles, rickshaws, bullock carts, etc. It has become very easy to cover long distances in a short time, thanks to the wheel.

          Before the invention of wheel, man himself carried the load. Later on, he started taming the animals like oxen, donkeys, horses and camels and used them for carrying their load. Gradually man started carrying load by dragging wood planks with the help of animals. Stone Age people may have learned to roll loads along on logs. The oldest known wheels looked like slices cut across a log with a hole in centre. Each solid disc was made of tree parts. After this invention, two wheels were joined by an axle and the axle was fastened to a platform of wood. This was the first crude cart of the world. In this cart both the wheels and the axle used to move.

          Later, a sophisticated version of wheel was developed. Wheels were made in ancient Mesopotamia (modern Iraq) between 3,500 BC to 3,000 BC. The picture of a cart wheel appears on some clay tablets from Mesopotamia dating 3,500 BC. About 2500 BC wheel was in use in Indus valley also.

         The next improvement in the use of wheel was fastening the axle to the vehicle and letting the wheels spin freely. The first wheeled vehicles were bullock carts, war- chariots and four-wheeled carts of the gods. Gradually the spoke wheel was invented in Asia about 2000 BC. This reduced the weight of the wheel considerably.

          With the passage of time, numerous improvements have been made in the design of wheels. Today, we have the rims and spokes of the wheels made of iron. Rubber tyres and tubes are put around them. To make tyres durable, nylon fabrics are used in rubber solution. Rubber tyres are so designed that these can have firm grips over the road surface to avoid skidding. Now wheel has become lighter, more efficient and long lasting. The invention of an unknown genius carried us a long way along the path of technology and civilization. 

          Archimedes, the “Father of experimental science”, was an ancient Greek physicist and mathematician. He was born at Syracuse in Sicily in the year 287 B.C. and educated in Alexandria. His teacher was a disciple of Euclid. The principles of science discovered by him are still taught to students. The famous “Archimedes’ Principle” tells us that if we weigh an object in air and then weigh it again when submerged in a liquid, it will apparently lose weight equal to the weight of the liquid it displaces.

          The story of discovery of the famous Archimedes’ Principle is very interesting. Once King Heron of Syracuse gave him a crown made of gold. He suspected that it was alloyed with silver. He asked Archimedes to test its purity without damaging it. It was absolutely a new problem for him. Interestingly he found its solution one day in a very peculiar manner. When he entered his bathtub, he found that his body displaced some water, and the water level in the tub rose. He then jumped out and ran down the street, naked, shouting “Eureka! Eureka!” (“I have found it! I have found it!”). He filled a vessel with water and dipped the crown in it. The water displaced by it was measured. Again he filled the vessel with water and dipped an equal mass of pure gold in it. The water displaced was again collected and measured. The amount of water displaced in the two observations was different. From this experiment he estimated the impurity in the gold crown. On the basis of this discovery he gave the method of finding out the relative density of different substances. 

          Archimedes also gave the laws of flotation of bodies and the principle of lever. He, for the first time, calculated the value of pi. In addition to these, he discovered the use of levers and pulleys and how to pump water uphill using Archimedean screw. The system is still used to irrigate fields in Egypt. He also designed war machines.

          Romans captured Syracuse in 212 B.C. At that time Archimedes had become quite old. One day while he was drawing some geometrical figure on the sand, one of the Roman soldiers asked him to accompany him. And when he refused, the soldier pulled out his sword and killed him. He was cremated with great honours. 

          Sir Isaac Newton is considered as one of the greatest scientists and mathematicians of all time. He was born on the Christmas morning of 1642 at Woolsthorpe in Lincolnshire. It was also the year in which the famous scientist Galileo died.

          At the age of twelve Newton was sent to school. When he was eighteen, he went to Trinity College at the Cambridge University. There he showed his brilliance in mathematics. In 1669 he became Professor of mathematics in the same college.

          Newton was very fond of making mechanical toys in his childhood. It is said that one day while sitting in a garden, he saw an apple falling to the ground. He began to wonder: “Why did the apple fall towards the ground? Why did not it go towards the sky?” Such questions puzzled him. He worked on this problem and finally gave his famous ‘Law of Universal Gravitation’. According to this law, everybody in this universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. He established the fact that the earth attracts all objects towards its centre. That is why anything thrown upwards falls back to the earth.

          Great scientist as he was, he solved many mysteries of the nature. He showed that the sunlight which appears white is in reality made up of seven colours. He could split these seven colours with the help of a prism. He also showed that the mixture of these seven colours produces white light. He also built the first reflecting telescope. His work on light and colour was published in 1704 in a book called Optics. He did monumental work in the field of mathematics. He gave the famous Laws of motion. He invented calculus. Newton’s discoveries were published in his book called Principia. It is one of the most important books of science ever published. On account of these researches Newton is called the ‘Father of Physics’.

          In 1689 Newton was elected as a member of parliament. In 1703 he was elected President of the Royal Society and was re-elected as president every year until his death. When he was 85 years old, he went to London to preside over a meeting of the Royal Society. But on his return he fell ill and he died on March 20, 1727.

 

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.