My Science School

               The world’s first underground railway was built in London city. Once the route was planned, a great trench was cut along the streets. Then the railway tracks were laid and the trench was covered over again, to restore the road and create a railway tunnel underneath. This method of tunnel making is called ‘cut and cover’.

               The original route of the London underground railway was nearly four miles long from Paddington Station to Farringdon Street in London. It was opened on 10th January 1863. The first trains were hauled by steam engines and the smoke in the tunnels caused discomfort. But this being the world’s first under-ground railway, it was a cause of great excitement. Today, the most extensive underground railway system in the world is in London.

               In 1890, a deep tunnel railway was also built in London through which electric trains could run. The earlier trains did not have any windows as they were thought to be unnecessary if the train was only to travel through a tunnel. The deepest underground point on the railway line is 67.3 m deep near Hampstead. The longest single journey is from Epping to West Ruislip which is 54.9 km long.

               Many other countries of the world also have underground railways. In Paris an underground railway was opened in 1900. In the United States of America the first practical subway line was constructed in Boston between 1895 and 1897. New York City opened the first underground railway in 1904, now the largest system in the world. The world’s busiest ever metro system has been the Greater Moscow in Russia (Opened in 1935).

               In Canada, Toronto opened a subway in 1954. In Japan, the Tokyo subway was opened in 1927. India’s first underground railway was inaugurated in Calcutta in 1985. This has relieved pressure on Calcutta’s traffic problems to a considerable extent.

               Construction of underground railways is a very complicated process. Normally deep trenches are dug by the side of main roads to lay rails. The walls of these trenches are made of bricks and are covered with strong steel beams to make the roofs. The trains run underground and other vehicles above them on the roads. 

               When we speak of intelligence we refer to the natural intelligence of people which means their inherent mental ability. But artificial intelligence is the intelligence of machines that can think like human minds. Of late, scientists have developed computers which can perform tasks that require intelligence. The successful performance of such tasks which need some thinking and analysis has again generated the old debate whether machine is superior to man or vice versa?

               Nowadays machines can easily recognize and read printed words. Autopilots, which are computerized machines, can fly aircrafts. These intelligent machines can also recognize and respond to sound and voice and also learn to rectify the mistakes committed. Even computers can play chess so brilliantly that they sometimes outwit the human beings. The whole world was stunned when an IBM computer defeated the world champion Gary Kasparov in a game of chess. But does this mean that artificial intelligence is superior to the natural intelligence of man?

               A computer carries out a series of operations as per the programs developed by computer programmers. This means that the human intelligence works behind the artificial intelligence of machines. Artificial intelligence has its limitations as it depends on the amount of stored information in it to make a decision whereas the natural intelligence is not handicapped by any such limitations.

               Now research is underway to create sound links with computers so as to enable them to recognize human speech and thus receive the feedback orally rather than inserting the instructions through the keyboard. This development of direct interaction with machines or computers would be another milestone in the field of artificial intelligence.

               Now artificial intelligence research covers the areas of planning, language understanding, and pattern recognition and knowledge representation. But whether it can ever surpass the natural intelligence of man, only the future can say.

 

               There is perhaps no human activity older, more varied or stranger, than fishing. He tricks and catches fish in different ways, such as using his bare hand, or fishing even with harpoon guns in whaling! But the method most used today is the one by which it produces the biggest share of commercial fishing known as trawling. Do you know how do trawlers fish?

               Trawlers fish with a bag-size net. It is let out on long warps or ropes. The fish are swept in at the wide, open end and then get trapped at the narrower, closed end. The trawler may be between 100 to 1500 metres long or more. In this system, the motorized fishing boats trawl by towing a large net in three different ways to keep the mouth of the net open. Firstly, a beam can be placed across the head of the net; secondly a pair of boats can be used - one at each side of the net to tow it and thirdly, some floating weights, called otter boards can be attached to the sides of the mouth of the net.

               However, the beam trawl is only used on a few small fishing crafts, and on the other hand, pair trawling is used to catch fishes from the bottom of the sea to enormous depths, sometimes at the range of 1500 metres or more. When the net is full, powered winches haul it on the board through a ramp. The otter trawl is widely used and is employed on almost every fishing technique except the smaller trawlers.

               The net gathers in everything including eggs, newly hatched fishes and algae. But this system is considered to be very destructive and alarming in the context of overfishing along the seas. Sometimes an entire fleet of fishing vessels is headed by a large factory ship fitted out just for processing of the catch. A single “sweep” of the net often taken in terms of tonnes of fish provides an idea of the quantity of fish caught in rich seas. Deep sea fishes like sardines and herrings together account for eighteen percent of the world’s catch.

               Today, the large motor fishing vessels are fitted with sonar or echo-sound equipments to locate a shoal of fish.

 

               You might say that the ball would fall behind the person who throws it because he would have moved forward with the moving train. But in fact this is not correct.

               You can perform a simple experiment to answer this question. You would be surprised to find that the ball lands right in your hand when thrown upward inside the moving train. Do you know why it happens so?

               In a moving train everything inside the train also moves with the speed of the train, for example, the fans, passengers, you and the ball in your hand. When you throw up the ball, a part of the speed of the train is imparted to it. It acquires a vertical motion in addition to its horizontal motion. The passengers in the train cannot see its horizontal motion but only its upward and downward movements.

               Imagine a man outside the train, who is watching your experiment. As we have said the ball possesses both vertical and horizontal motions, both these motions combined together make the ball travel along a parabolic path. The observer outside the train will see the ball moving in a parabolic path but a passenger in the train will see only the up and down motions of the ball.

               Now the question arises whether the ball follows the parabolic path or just moves up and down? Out of these two which one is right? In fact, all motion is relative to the observer. There is nothing like absolute motion and hence the motion of the ball is different for the two observers. 

               When you push the button of an electric door bell or calling bell it keeps on ringing as long as the button remains pressed.

               Do you know how does it function? An electric bell is a simple device based on the magnetic effects of electric current. It is used in offices, houses, industries and for fire alarms.

               It consists of a U-shaped electromagnet and a soft-iron armature. The armature has a small hammer for striking the gong. This hammer hits the gong repeatedly and produces sound. The gong is made of a metal. For operating the bell, a push button is pressed. In an electric bell, the button is a switch that connects the supply of electricity to the bell.

               When the button of the bell is pressed, the current flows through electromagnet winding, armature, contact spring and the contact screw. The flow of the current magnetizes the soft-iron core of the electromagnet. This attracts the armature, causing the attached hammer to strike the metal gong and thereby produce sound.

               As the armature moves forward due to magnetic attraction the contact spring moves away from the contact screw. This breaks the circuit and the current stops flowing. As a result, the soft-iron core loses its magnetism. It, therefore, no longer attracts the armature which, then, is pulled back by the contact spring to its original position. As soon as the armature comes to its original position the electric circuit is again completed and the soft iron becomes magnetized. It again attracts the armature and thereby the hammer strikes against the gong and produces sound. As long as the push button remains pressed, the circuit is alternately broken and completed causing the hammer to strike the gong. Thus an electric bell keeps ringing.

               If a steel core is used instead of a soft-iron, then the steel core will become a permanent magnet due to passage of electric current through the winding. Consequently, the armature will stay attracted even when the contact spring moves away from the contact screw, so the hammer will strike the gong only once.

 

               It is a well known fact that when resins are put in water they get swollen. This swelling takes place due to the entry of water through the membrane of the resins. Similarly, if grapes are put in sugar solution they shrink. Swelling of resins and shrinking of grapes take place due to a process known as osmosis. Do you know what this osmosis is?

               Osmosis is a process in which a solution of lower concentration passes into a solution of higher concentration through a semipermeable membrane. A semipermeable membrane is one that allows some, but not all, substances to pass through it. This contains very small pores. When resins are put into water, the covering acts as a semipermeable membrane. Water is less concentrated than the substance present inside the resins and so the water moves into the resins through its semipermeable membrane. Similarly, fluid from grapes moves out through the semipermeable membrane, as the concentration of sugar solution is more than that of the grapes. There is a tendency for solutions separated by a membrane to become equal in molecular concentration.

               In osmosis, the movement is always from a dilute solution into a solution of higher concentration. This reduces the concentration of the stronger solution. The rate of osmosis depends upon the comparative strengths of the two solutions. The greater the difference, the faster the rate of osmosis. This process continues until both solutions are of equal strength. When this equilibrium is reached, osmosis stops.

               Osmosis is an ongoing process among the living beings. The membranes of cells are semipermeable. Plants absorb water and dissolved minerals from the soil by osmosis; they use osmosis to move the water and dissolved minerals through the plant, cell by cell. Osmosis also maintains turgor pressure. Turgor pressure is the pressure of water on the cell. It gives the cell form and strength. When there is a decrease in turgor pressure, the plant will soon wilt and lose its regular stiffness.

               Osmosis allows the transfer of water and dissolved nutrients in the human body from the blood into the cells.

 

Electric heaters, immersion heaters, electric irons, electric kettles, etc. are appliances which produce heat through electricity. All these appliances are based on the heating effects of electric current. When electric current is passed through a wire, it gets heated up. Heating of a wire depends upon two facts: first, on the resistance of the wire and then on the amount of electric current passed. The heat produced in the wire is directly proportional to the resistance of the wire and that of the square of the current. The amount of heat produced also depends upon the time for which the current passes through the wire.

Based upon this property of current, many domestic electric appliances have been developed. The working principle of all these appliances is almost the same, the difference lies only in their construction. An electric heater consists of a coil of nichrome wire which is in the form of a spring. This coil is mounted on an insulating base plate made of clay. When electric current is passed through the coil, it gets heated up. Room heaters are also made in a similar way, the only difference being that nichrome wire is wound around an insulating rod and a reflector is mounted at the back of the coil which reflects the heat radiation.

Immersion heaters also consist of a nichrome wire which is enclosed in a metal tube. To isolate the wire from the metal tube, an insulating powder is filled in the tube. This powder acts as an insulator for electricity but conducts heat. When the two terminals of the wire are connected to an electric source, the current starts flowing through the wire and it gets heated up. The immersion heater is put inside a bucket full of water to heat the water.

An electric iron is used to remove the wrinkles from washed clothes. This appliance also consists of a ribbon of nichrome wire which is enclosed between two sheets of mica. This spreads the heat uniformally along the base plate of an electric iron. Mica sheets are mounted on a heavy metal plate. This metal plate, when pressed against the surface of the cloth, removes the wrinkles from the cloth.

Electric irons are of two types: automatic and manual. Automatic one is fitted with a thermostat control which regulates the temperature. Manual irons do not have such a device. When the iron is cold, thermostat provides and maintains a constant temperature by the use of a device that cuts off the supply of heat when the required temperature is exceeded.

An electric kettle is used to prepare tea or coffee. It also consists of a heating element fitted at the bottom of the vessel and is isolated from it. Water is put into the vessel which gets heated when current is passed through the heating element.

For all electrically heated appliances, it is very essential to have an earth connection. Immersion heaters should not be switched on, until there is water in the bucket. The electric bulb is also a similar device whose filament gets heated up when the electric current is passed through it and it produces light.

 

               Electric fans have become an essential part of our lives. It provides a cooling effect during the summer and rainy seasons. Do you know how does it work?

               An electric fan is a device which converts electrical energy into mechanical energy. It works on the basis of magnetic effects of electrical currents.

               The heart of an electric fan is an electric motor. So before understanding the working of a fan, it is essential to know the working principle of an electric motor.

               In its simplest form, it consists of a coil or armature through which the current flows. It is connected with a spindle. This coil is placed in between the poles of a magnet. When the electric current flows through the coil, it starts rotating due to the magnetic effects of electric current. This motor consists of a split-ring commutator to which two carbon brushes are attached. The armature of the motor is connected to a metal shaft. At the other end of the shaft, three or four blades made of a light metal are attached which also start rotating along with the motor. These blades are designed in such a way that when they rotate, they suck in air from one side and throw it to the other side, thus causing strong air currents. 

               The speed of rotation of the motor can be controlled by controlling the current which is done with the help of a regulator. This regulator consists of a resistance which controls the amount of electricity flowing through the coil.

               Usually electric fans are of two types: ceiling fans and table fans. The domestic electric fans are usually rated from 60 watts to 120 watts.

               A third type is often used in underground establishments, kitchens, cinema halls, stores etc. to expel the polluted air. These are called exhaust fans. The blades of these fans are so designed that they suck in the air from inside and throw it outside. These are also used in air coolers.

               Now the question arises as to how the air of the fan gives us the cooling effect? The fan increases the speed of air currents and this brings about an increase in the rate of evaporation. Since evaporation causes cooling, a running fan produces a cooling sensation.

 

            Wax is an insoluble solid fatty substance that is widely used as a protective covering for different kinds of surfaces. It is also used for making candles and polishes. Waxed paper is an item of our daily use. Do you know how wax is made?

            Normally wax is solid at room temperature but softens and becomes sticky when heated. Many fruits and vegetables, and leaves of many plants have a thin protective coating of wax. It is useful in protection of organisms. Many animals also produce wax. We get wax in large quantities from minerals and petroleum. Nowadays synthetic methods have been developed for the manufacture of wax.

             Depending upon the source from which wax is obtained, we classify wax into four kinds: (i) mineral wax (ii) animal wax (iii) vegetable Wax and (iv) synthetic wax. Paraffin wax is a kind of mineral wax which is taken out of petroleum. This is quite hard in nature. Petroleum jelly is a kind of soft wax and is used for medicinal purposes. More than 90 percent of all commercial wax used today is petroleum wax. This is very useful because it is odourless, tasteless and chemically inactive.

            Animal wax, such as bees wax produced by bees, is used for making candles, cosmetics, polishes, crayons and artificial flowers. We get wool wax from wool-bearing animals and are called lanolin when purified. Lanolin is widely used for manufacture of moisturizer and skin creams.

            We get several kinds of wax from plants. Carnauba wax is obtained from the leaves of the carnauba palm trees of Brazil. This wax is hard and gives an excellent brightness when used as a floor and furniture polish. Candellilla wax comes from a plant of the same name that grows in Mexico and the South Western United States. It is a brown wax used in phonograph records, floor dressings and candles. Bay berry wax from the berries of this shrub is used for making candles.

            Synthetic waxes are chemical combinations of hydrogen, carbon, oxygen and sometimes chlorine. They are made according to different formulae to have definite properties.

 

               Mixer and grinder are very useful domestic appliances. With the help of these appliances we can grate, grind and prepare mango shake, milk shake, cold coffee etc. in a short period of time. Butter can be extracted from cream by using this apparatus. Pulses and spices can also be ground easily with its help.

               This apparatus consists mainly of two parts. One is the base of the apparatus which is fitted with a high speed motor. This motor makes 15-20 thousand revolutions per minute. It also consists of a variable switch by which the speed of the motor can be adjusted with the other part of the apparatus known as a mixer and grinder. This is usually made of stainless steel or plastic in the shape of a jar. It is fitted with blades which revolve with the speed of the motor. This rotating blade minces the food material into small pieces.

               Modern mixer and grinders also consist of other attachments such as a juicer with the help of which we can extract the juices of apples, oranges, tomatoes and other fruits and vegetables. In this attachment juice pours out on one side and pulp from the other side. Most modern grinders and mixers can be fitted with various other attachments such as a slice grater, meat mincer, dough maker etc. Nowadays we have grinders by which even wheat or maize can be ground.

               These electrically operated machines have minimized the tedious work in a kitchen. Not only do these machines save time but also provide neat, clean and tasty food for us. Moreover, these machines do not consume much electricity.

                Ammonia gas is a colourless non-poisonous gas that has pungent smell and strong irritating effect on the eyes, nose, throat and lungs. It is highly soluble in water and a compound of nitrogen and hydrogen. One atom of nitrogen on combining with three atoms of hydrogen forms one molecule of ammonia. This gas can be liquefied by compressing or by cooling at -33°C. At normal temperature and pressure, 700 volumes of ammonia can dissolve in one volume of water. Its solution in water is basic in nature and is known as Ammonium Hydroxide.

               There are several methods of making ammonia gas. In the laboratory, this gas is prepared by heating a mixture of ammonium chloride and lime. On a large scale, this gas is manufactured by causing a chemical reaction between hydrogen and nitrogen. This method is called Haber’s Process. In this process one part of nitrogen and three parts of hydrogen are mixed and compressed to 500°C in the presence of iron which acts as a catalyst. Ammonia can also be obtained by distilling coal into coke and coal gas.

                Ammonia is very useful to us. It is used in the manufacture of many of its compounds and also for making nitric acid which is used to dissolve many dry cells. This is also used in the dyeing and printing industry.

                Ammonium sulphate is an important compound of ammonia. It is made from ammonia and sulphuric acid. It is used as a fertilizer because it provides nitrogen for the soil. Ammonium nitrate is used in fertilizers, explosives and for making nitrous oxide, also called, ‘Laughing Gas’.

               The ammonia used as a household cleaner is a strong solution of gas in water. It is also used as cooling agents in refrigerators.

 

               In a football match it is our common experience to see that when a player kicks a resting ball it moves in a certain direction. Similarly when the goal keeper grabs the ball firmly with his hands it stops moving and remains at rest till it is released again. Do you know why it happens so? In both these actions force is applied on the ball.

               Force is a physical quantity which, when applied to a body tries to displace or displaces it. This quantity is equal to the product of the mass of the body and its acceleration. The unit for measuring force is Newton or Dyne. Force is required to set any body in motion and this force is applied in a particular direction. The force is an external agency capable of changing the rest or motion in an object or a body. When force is applied on a body and it gets displaced, we say that work has been done on the body by force. The amount of work done by the force is equal to the product of the force and the distance covered by it. A work done by force is measured in Joules. In short, force is a vector quantity possessing both magnitude and direction. 

 

 

 

           

   The capacity of doing work is called energy. Everything in the universe has some energy by which it can do some work. We experience energy in many forms such as mechanical energy, heat energy, light energy, electrical energy, magnetic energy, chemical energy, nuclear energy etc. 

 

 

 

 

 

 

             Mechanical energy is of two types: potential and kinetic. Potential energy is due to the position of the body while kinetic energy is due to the motion. One form of energy can be converted into the other form of energy. Winding a watch spring stores potential energy. This stored energy gets converted into kinetic energy when the watch starts running. Although energy can be converted from one form to the other, yet the total quantity remains the same. 

 

 

 

 

 

               Some people confuse between power and energy and think of both as the same. But it is not so. Total energy of a body is equal to the capacity of the work done by the body while power is the rate of doing work by the body. It is equal to the amount of work done in unit time. The system to measure unit of power is called horse power (hp) or watt. Horse power is the British unit of power. 

 

 

 

 

 

 

               One horse power is equal to 735.7 watts. The word ‘watt’ is derived from the International Systems of Unit and named after the British engineer James Watt. 

               Embossing is the process of producing raised patterns on a surface. This is one of the oldest methods to decorate metals. A technique widely used for making ornaments is in which a thin metal sheet is decorated by beating it on the underside. This type of embossing is usually done either by hand or with a die and a counter die. It is usually called repouses. The materials suitable for embossing are plastics, thin metals, papers and leathers etc.

               Crests, monograms, and addresses may be embossed on paper envelopes from dies set either in a small hand-screw press or in an ordinary letter press.

               For impressing embossed pattern on wallpapers, textiles, copper cylinders are engraved with the desired patterns to be raised.

               In this process the pattern is drawn or inscribed on the face of the die called male die. The surface is then machined away around the pattern so as to leave it raised. The counter-die termed as female die is engraved to match this die, so that when a thin strip of metal is placed between them and the die is forced into the counter-die, the pattern is left impressed or embossed upon this thin strip of metal. Die stamping has been used for many years for manufacturing metal parts. This method is also used in stationaries and letterheads. In this method paper is pressed between the dies and ink is applied to the top surface at the same time. Printers nowadays are using embossing machines for this purpose which produce raised patterns in a very short period of time. Blocked ornamental design on book covers or imitation tooling on letter work for instance, can be beautifully affected by means of powerful embossing presses.

               Small hand-operated embossing machines have become very popular. The letters and numbers are embossed on a strip of soft metal or more commonly used vinyl tape. These are then formed by the hand-operated embossing machine. A wheel is used for pressing which transfers the pattern onto the other strip.

               Modern embossing machines are equipped with latest electronic devices. They are replacing the hand-driven machines gradually. But still, a few traditional users of embossed material, such as ornaments prefer the old technique in making their ornamental designs.

 

               We all have seen the digital watches and calculators. These devices make use of liquid crystals for displaying various digits. Liquid crystals belong to a state of matter having the mixed properties of both the liquid and the solid states. Liquid crystals may be described as condensed fluid states with spontaneous anisotropy.

               Liquid crystals are of two types: thermotropic liquid crystals prepared by heating the substance and lyotropic liquid crystals made by mixing two or more compounds. Some of the important liquid crystals that belong to the first category are p-azoxyanisole, cholesteryl nonanoate and p-n octyloxybenzoic acid. In the second category sodium stearate and alpha-lecithin are the two important liquid crystals. Liquid crystals are used in colour T.V. and electronic display tubes, sensitive tapes and electronic devices for digital clocks, watches and calculators.

               Light emitting diodes are also used for this purpose but liquid crystals need lesser electric power and have great clarity even in the presence of bright light. 

               Liquid crystal displays work on two principles, viz dynamic scattering and field effects. In displays the liquid crystals are sandwiched between two transparent electrodes (glass coated with a metal or metal oxide film). The thickness of a liquid crystal film varies from 6 to 25 microns. The cell is sealed to eliminate oxygen and moisture.

               In dynamic scattering, if no electric field is applied, the cell is transparent. On applying electric field to the crystal the cell becomes opaque. Digital displays are made by photo etching a seven-segment pattern on tin or indium-coated glass plate.

               The field-effect displays are mostly used in watches and calculators. The output of quartz crystal is given to seven segments of liquid crystal in a watch. Polarizers are also used for liquid crystal cells. Electric field changes the molecular alignment by which liquid crystal becomes opaque on account of a mirror behind the second polarizer.

               Liquid crystal displays have revolutionized a number of fields. Nowadays thermometers with digital displays are also available in the market. 

            When someone wants to take a photograph in dim light or darkness, he makes use of a flash-gun with his camera. As soon as the shutter of the camera is pressed, flash gun produces its own light and illuminates the object. Do you know how does a camera’s flashlight work?

            A modern flash-gun consists of a light source which is usually a xenon flash lamp. To operate the flash lamp there are electrical circuits and an electric source which gives energy to the flash lamp. Electric source is usually a dry battery.

            A xenon flash lamp is a glass tube - usually two inch long with quarter inch diameter. Two tungsten electrodes are sealed at the ends of this glass tube. This tube is evacuated and filled with xenon gas at a pressure of 400 to 500 mm of mercury. A thin wire is wound around the tube which acts as the third electrode and is known as trigger electrode. The two electrodes of the lamp are connected to the electric circuit which consists of a capacitor bank to store the electrical energy. When shutter is pressed, the electric switch is also pressed and a high voltage pulse comes on the third electrode. This high voltage pulse ionizes the xenon gas by which it becomes electrically conducting. At this point, the energy stored in the capacitor bank gets discharged through the xenon lamp. As a result light is produced which illuminates the object to be photographed? At the back of the xenon lamp, a reflector is mounted which directs the light towards the object.

            Unlike a flash bulb, an electronic flash can be used again and again. The flash contains a tube that gives out a bright flash of white light when a strong electric charge passes through it.

            The light emitted from the flash gun is in the form of a pulse. Its duration is about one millisecond but the light is very intense. Nowadays almost all cameras are fitted with the electronic flash devices.