What is Electricity?

            In ancient times, man took the flash of lightning during a thunderstorm as a signal of impending destruction from the heavens or the displeasure of god. With passage of time, science progressed and the mystery of this great energy called electricity unfolded.

Layout of Thermal Power Station

            As early as 600 B.C. Greeks discovered electricity by rubbing amber with cloth, which enabled it to attract small pieces of papers. In fact, the word electric originated from the Greek word electron. Based on the theory of electromagnetic induction of Michael Faraday in 1831, first successful generator or dynamo was made in Germany in 1867. U.S.A. produced electricity by running turbines with the help of falling water in 1858.

            Today, we cannot imagine the normal life without electricity. We know it as a form of energy that powers almost all machines or mechanical devices- trains, radios, television sets, freezers and so on.

            Electricity is a phenomenon involving electrical charge and its effects, either at rest or in motion. Electricity that we use flows through wires as electric current. Electric current, which flows through a conductor of a given resistance, produces heat. Particles of a matter may be positive, negative or neutral. We know that electricity has its two important particles- protons and electrons. Electron is negatively charged while a proto is positively charged. An element containing an equal number of protons and electrons is electrically neutral. For example, anode is a positive electrode while cathode is a negative one.

            Electricity that we use is produce in power stations. In the generator of a power station, coils of wire are made to rotate between powerful magnets, which induce electric current into the coils. The electricity produced is further distributed through metallic wires. Materials through which electricity can travel are called conductors, i.e. substances like copper, aluminum and iron. Materials through which electricity cannot pass are called insulators, i.e. materials like rubber, wood and glass.

            After the invention of the electric cell by Alessandria Volta, man realized that light heat, chemical reactions and magnetic effects could be produced from electricity.

            Electricity, which flows in one direction and then in the opposite is called alternate current (A.C.). Each movement of A.C. back and forth happens very quickly-about 50 times in a second. The electricity that we use at houses is normally A.C. steady flow of current in one direction is known as direct current (D.C.) for example, battery current is D.C.

            Today, hydroelectric and thermal power stations are the most popular methods of producing electricity. During the 20th century, many nuclear power stations were constructed to meet the growing demand of electricity.

What is a Bolometer?

            Bolometer is an instrument that is used to measure radiation temperature. It is a kind of Resistance Bridge. Its one arm consists of a blackened metal strip. When the radiations fall on the metal strip the temperature rises. This increase in temperature measured by a bolometer. This is a very sensitive instrument.


            A U.S. scientist, Samuel P. Langely invented this instrument in 1880. In this first bolometer, a Wheatstone bridge was used along with a galvanometer that produced a deflection proportional to the intensity of the radiation. Since then several other thermal devices have been developed but bolometer remains one of the most effective and convenient infrared detectors. It is because it does not need cooling and can be operated with great ease.

            Now the question arises, what is the principle of working of this instrument? The principle on the basis of which a bolometer operates is that a temperature changes is produced by the absorption of radiation this causes a change in electrical resistance of the material used in the fabrication of the bolometer. This change in resistance can be used to sense radiation.

            There are several types of bolometer in use today. One type has two strips bridge the circuit, their electrical resistance changes. The change of resistance can be used to measure the temperature. This instrument is so sensitive that it can detect changes in temperature as small as 0.001 degree centigrade.

            Another type of bolometer known as spectrum bolometer consists of a single strip of metal. It is used for examining the distribution of intensity of radiation in a spectrum.

What is the Refraction of Light?

            If you dip a pencil in a bowl of water and observe the shape you will see that the pencil seems to be bent near the surface of water. This is due to a phenomenon known as refraction. Refraction of light is defined as the change in direction of a ray of light as it passes from one medium to another, i.e. air to glass or vice-versa. Refraction occurs because light travels at different speeds through transparent materials of different densities. For example, light moves at about 300,000 kilometers per second through air, but slows down in water, and much slower in glass.

Refraction of Light

            When a ray of light passes form a rarer to a denser medium, it bends towards the normal and when it is the other way round, it bends away from the normal. The normal it defines as the perpendicular line to the interface of the two media. Also when a ray passes form one medium to another, its speed also changes. If the ray goes form a rarer to a denser medium its speed decreases and vice-versa.

            When a ray of light passes fro, air into glass, it bends towards the normal. When it passes out into air again it bends away from the normal.

            There are two basic laws of refraction.

            The first law states that the ray that hits the surface called the incident ray and the ray that travels in second medium called the refracted ray and the normal all lie in the same plane.

            The second law is called the Snails law which states that the ration of the sine of the angle of incidence to the sine of the angle of refraction is constant. The constant depends on the material through which the light passes. It is termed as refractive index.

            The phenomenon of refraction explains many interesting facts. A coin in a bucket of water appears risen due to this phenomenon. The mirage in the deserts is also caused by refraction and total internal reflection of light. The twinkling of stars in caused due to he refracted light beams in the different layers of the atmospheric air.

How does a Video Telephone Work?

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

Video Telephone

            A complete video telephone system consists of the following parts:

1.                   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 up to 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 arrangement? At the receiver end these signals are converted into voice and picture which can be heard and seen by the person at the receiver end.

            Video telephone system was developed in 1927 by H.E. lves who transmitted one way images by wire from Washington D.C. also transmitted from blew jersey to New York by radio. These experiments were aimed at transmitting and reproducing a recognizable human face.

            In 1930, lves 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. Call 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 8 cities, including Moscow, Kiew 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 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. Early service between Chicago and Pittsburgh provided valuable insight into customer needs, but customer acceptance did not meet the early expectation.

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

How does a Parachute Work?

            A parachute is an umbrella like device used for slowing the descent of a body falling through the atmosphere. Originally, it was conceived as a safety measure for a fighter pilot in a flying aircraft. Now parachutes have wide application in times of war and peace; for example, they are used for safe dropping of supplies of essential items in times of emergency as well as for landing of personnel.


            The first man to demonstrate the use of parachute was Louis Sebastian Linesman of Franc in 1783. AndrĂ© Jacques granaries was first to use a parachute on regular basis demonstrating a number of exhibition jumps including one from a height of about 2400 meters in England in 1801.

            Early parachutes were made of canvas and later silk was used. Captain Albert berry of the U.S. army made the first successful descent from an aero plane in 1912. in world war II, parachutes were used for a variety of purposes i.e. landing of special troops for comber infiltrating agents into enemy territories and dropping of weapons, etc. parachutes are made of nylon and are generally about 7 to 9 meters wide, when open. Parachutes used for dropping heavy cargo may be as wide as 30 meters when open.

            Now the question arises how doe s a parachute works?

            A parachute operates on the simple principles involving the force of gravity and air resistance which are the two forces that act upon any falling object. A parachute starts falling towards the ground due to the force of gravity but due to resistance of air caught in the open parachute the speed of the fall slowed down.

            During the descent of a parachute at a certain point when the air resistance and the pull of gravity are evenly balanced the parachute reaches a speed called terminal velocity. At this stage parachute descends at a constant speed.

How does a Hair Dryer Work?

            Sometimes, when we visit a hairdresser’s shop for cutting or shaping our hair we find them using an appliance for drying hair. This is known as a hair dryer. Now, how does this hair dryer work?

Hair Dryer

            We are aware of the fact that the electric heater, electric bulb, immersion heater, etc. are domestic appliances, which work on the heating effects of electric currents. Hair dryer also works on the same principle.

            A hair dryer consists of a cover usually made of plastic, and shaped like a pistol. Inside this plastic cover, electric current is passed though a coil of nichrome wire and it gets heated up duet o the high resistance offered by the coil. At the back of this coil, a small electric fan is fitted.

            The hair dryer has two switches; one operates the fan the other allows the current to pass through the nichrome coil. When the first switch is put on, the electric fan starts running and the cold air comes out form the dryer, and when the second switch is put on, the coil gets heated up and as a result, the air now passes over the heated coil and gets heated. The hot air blows moisture-laden air away from the hair, thus drying them.

            This apparatus is not only used to dry hair but also for drying in the research laboratories in a number of experiments where drying process is necessary.

How Fast do the Objects Fall?

            When we know a ball up in the air, we observe that it gradually slows down, and the almost comes to a stand still, before it stars falling back to the ground. While it starts falling back to the ground. While falling down, it should be noted that the initial speed is low but gradually becomes high.

            The earth attracts all objects towards its centre with a force known as the force of gravity. The ball falls to the ground due to this force gravity. The force of gravity makes all falling objects acquire an acceleration, which is called the acceleration due to gravity. It is denoted by ‘g’.

            The acceleration due to gravity accelerates the ball roughly at 9.8 meters per second per second 32 feet per second. This means that each second the object would move 9.8 meters faster than the previous second. The speed of the ball at different intervals of time varies as follows.

            To begin with, the ball or a falling object is stationary or its speed is zero. At the end of 1 second, it travels 9.8 meters per second. At the end of 2 seconds, it moves 19.6 meters per second and at the end of 3 seconds, 29.4 meters per second and so on. In fact, every second, the object falls 9.8 meters per second faster than its speed in the previous second.

            Acceleration due to gravity is defined as the rate of change in velocity of a falling object with respect to time due to the force of gravity. Because it is measure of rate of change of velocity, it is expressed in meters per second, and is termed as meters per Second Square.

            The acceleration of body or object falling freely in vacuum varies slightly form place to place due to slight variation in the gravitational force of the earth, as the distance of the place form the center of the earth varies. In London, the value of ‘g’ is 9.807 meters per second per second, as North Pole 9.8 meters per second per second, and at the equator it is 9.79 meter per second. At sea level in Washington, it is 9.8008 meters per second per second.

            One of the important points to note about falling objects is that however heavy they might be, they all fall at the same rate. But, air resistance may retard the speed of falling objects. The famous scientist Galileo demonstrated this fact by dropping a heavy cannon ball and a light musket ball at the same time form the leaning tower of Pisa. Both the objects hit at the ground at the same time.

            Air resistance is the main reason why some objects fall slower than others. A feather, for example, floats slowly downwards because it faces more air resistance due to its relatively large surface area. A smooth, pointed bullet will fall faster than a feather because it experiences less air resistance. In vacuum both objects will fall at the same speed, as there would not be any air resistance.

What is a Pyrometer?

            A pyrometer is an instrument used for measuring very high temperatures-especially those that can not be measured through ordinary thermometers. For example, pyrometer is used to measure furnace temperature.


            There are two main kinds of pyrometers-radiation pyrometer and optical pyrometer.

            In a radiation pyrometer, the radiation form the hot object is focused on to a thermopile, which is a collection of thermocouples. When the thermopile gets heated due to the intercepted radiation, it produces a voltage. The amount of voltage developed depends upon the temperature. Paper calibration permits this electrical voltage to be converted into the temperature of the hot object.

            Sometimes, a bolometer is used instead of a thermopile. A bolometer has two strips of the platinum metal. When the platinum strips heat up, the electrical resistance of the strips changes. The change of resistance can be used to measure the temperature. Such pyrometers are sometimes called resistance pyrometer.

            Optical pyrometers use the color of light of the hot object to measure its temperature. Optical pyrometers, for example, measure the temperature of incandescent bodies by comparing them visually with a calibrated incandescent filament. The calibrated light indicates the temperature for various stages of temperature change. As the object gets heated the color changes, which are compared with the matching color. When the color is matched, the temperature is read off from the display unit.

            The voltage can be changed to maintain a constant color or temperature as required. A part form the main kinds of pyrometers, two other kinds are recognized as important by physicists. They are: (a) Platinum Resistance Thermometer (b) Thermo-Electric Thermometer. The pyrometers are also used to measure temperature form a long distance by making use of the law of radiation.

What is a Rangefinder?

A rangefinder is an instrument used to measure long distances. It is mostly use by surveyors and the army for a number of purposes. Rangefinders are mainly of two types’ optical rangefinder and laser rangefinder. Radars are also used as non optical rangefinder. They measure the time lapse of an electromagnetic wave which it emits and translates the time lag its echo into distance.


            Military rangefinders are usually long tube with eye pieces at the centre. Lenses and prisms are located at each end of the tube.

             One prism is fixed and the other can be moved so that it can be adjusted on to the object. The operator looks through the eye pieces and adjusts the movable prism so coincide with each other. The difference in the angles of the two lines of sight from the ends of the tube is called the parallaxes angle. The angle depends upon the distance of the object. The angle is measured on a dial fro which the distance of the tarter can be read directly.

            There are two types of optical rangefinders coincidence a stereoscopic.
            In the coincidence rangefinder the operator looks through a single eye piece and sees two images of the target. By turning a knob these two images move together target can be read on a dial.

            In case of a stereoscopic rangefinder the operator look  through a pair of eye pieces. One sees a single image of the target as well as a marker that seems to be floating I space near the target. The operator turns a knob until the marker seems to be at an equal distance as that of the target. Than the distance is read on dial.

            The laser rangefinder works on the principles of radar. A laser beams is emitted at the target and the time taken by the laser reflected beam from the rangefinder to the target and by the velocity of laser light gives double the distance to the target. All one has to do now is to divide it by two to find the distance to the object.

            These rangefinders today give the range to the object directly. In modern warfare the laser range finder is absolutely necessary to locate targets and enemy positions from a distance. Spy satellites are also used for the same purpose.

How does a Siphon Work?

A siphon is a device used to transfer a liquid from one container to another. It is shaped like a bent tube with arms of unequal length.

Siphon is used to transfer liquid from one container to another

            A rubber or plastic tube is normally used as a siphon. One end of the tube is placed in the container containing the liquid to be transferred. The liquid is sucked from the other open end, which must be at a lower than the liquid level in the first vessel. Once the liquid starts flowing out it will continue till the levels in both the containers are the same or the first container is empty or till the liquid level in the first container goes below the siphon tube level.

            What makes the liquid flow from one container to the other?

            It is air pressure which forces the liquid to flow fro the first container to thee second provided the level of liquid in the first container is higher than that in the second one. Because of the difference in the lengths of the arms a pressure difference causes the liquid to flow. Since the upper liquid is usually exposed to the atmosphere the maximum elevation over which a water siphon will function is water equivalent of atmospheric pressure.

How is Paints Made?

Paint is a mixture of one or more colored powders and a liquid usually oil. The colored powder is called a pigment. The liquid is called a vehicle or binder. The vehicle carries the pigment and allows it to spread over the surface. Many vehicles contain a solvent or thinner.

            There are basically two types of pigments prime pigment and inert pigment. Prime pigments give the paint its color, and inner pigments like calcium carbonate, clay, mica or talc make the paint durable.

            Vehicles include oils, varnishes, latex and various types of resins. When a vehicle comes in contact with air, it dries and hardness. This makes the pigment bind with the surface.

            There are various types of paints. The paints used on walls and roofs are oil-based. Such paints serve to protect wood and metals. Latex paints include wall paints and masonry paints.

            Many masonry paints are produce with substances like polyvinyl acetate or acrylic emulsions. Lacquers are often used to paint automobiles. It is made of a solution or resins in a solvent. It is made of a solution of resins in a solvent. The solvent dries up after the lacquer is put over it. There are fire resistant paints that protect material against damage due to fire. Heat resisting paints are used to cover warm and hot surfaces.

            Cement water paints add color to cement surfaces such as a basement floor. In metallic paints, aluminum or bronze powder is used as ingredients. Enamel paints contain small amounts of prime pigments. They are often used in bathrooms and kitchens.

            To manufacture paint, a small amount of the vehicle is put into a large mechanical mixer. Then powdered pigment is slowly added to the vehicle, and a heavy paste of these two is made. The paste is put into a grinder to break up the pigment particles, and spread the evenly throughout the vehicle. This operation is followed by thinning and drying. The paint is treated until the solution is thin enough for use.

            Tinting is the next process. A tinter adds a small amount of pigment to give the paint the desired color and shade. The final steps include straining and packaging. The paint is straining and packaging. The paint is strained through a filter to remove any solid particles of dust or dirt. It is then poured into a filling tank, and finally into metal cans in which it is sold.

What are the Contact Lenses?

            The contact lenses are worn directly on the cornea of the eyes to correct defects in vision. All the defects that are corrected by regular eyeglasses and those which cannot be corrected with glasses can now be rectified by contact lenses.

Contact Lenses

            The first contact lens to be used as an eye aid was made by A.E. Fick in 1887. These early lenses were first made by blowing glasses and then by grinding and polishing the bottoms of glass test tubes. These lenses were not successful and remained just a subject of academic study for a long time. Progress was made only in 1938, when plastic (methyl methacrylate) contact lenses were developed. Form 1938 to 1950, the process adopted for making contact lenses was not simple. First the impression of the eye was taken, then a mould was prepared and then the lens was made out of it. Such lenses had a fluid under them and covered most of the eye.

            After 1950, smaller lenses were used that covered only the cornea, which is the front surface of the eye, and floated on layer of tears. It was no longer nec3esar to make an impression of the eye. Optical instruments could measure the curvature of the cornea. Such lenses are usually 7 to 11 millimeters in diameter and 0.1 to 1 millimeter in thickness and can be worn all day.

            To fit the contact lenses, the eyes are first tested for defects just as they would be in case of spectacle. Then the radius or curvature of the eye surface is found out by using a device called kerometer. After deciding on the diameter and power of the lens, the prescription is sent to the manufacturer for making the lens.

            Contact lens are made by taking a plastic rod which is first sewn into sections and then turned on a lathe to make button shaped tablets, know as bonnets. They are given the right curvature with the help of special machines for obtaining the desired power and then finally polished. The lenses are then examined to see whether they fit the eye. Finally, they are worn on the cornea. These lenses can be worn comfortably by most people throughout the day.

            Contact lenses save the bother of wearing spectacles; contact lenses provide a much wider field of vision than ordinary spectacles. They are better for active sports, since they are not easily lost or broken, and can even be used to protect against the sun. Contact lenses cannot correct all defects of the eye. They are also expensive and some people have difficulty in wearing them. In some cases people have experienced irritation after wearing them.

            As research continues, smaller and more flexible lenses are being developed in order to make them less irritating to the eyes. Soft lenses of hydroxyethyle are used today in the manufacture of contact lenses.

What is FM Transmission?

            Over the year frequency modulated FM transmission has attained wide popularity due to its clarity and high fidelity in reproducing the broadcast speech or music. It can also provide a stereophonic effect to the sound produced at the receiving end. Before television came into our homes, radio was a popular entertainment medium. With FM transmission capturing the imagination of people, radio is likely to become popular once again.

FM Transmission Provider

            The earlier transmission services were basically amplitude modulated AM, which could not filter the noise and hence lacked the clarity that FM can provide. But what is the fundamental difference between AM and FM transmission?

            In both AM and FM transmission, radio waves are modulated by mounting it on the carrier frequency, which is essential for broadcasting and propagation. In AM transmission, the waves are constant in frequency but the amplitude varies, whereas in FM transmission, the amplitude is constant and the frequency varies. In simple terms, in AM amplitude is modulated and in FM, the frequency is modulated.

            Modulation is the process of coding the sound waves for transmission, and is done either by altering the amplitude of the wave or its frequency.

            We now need to understand three fundamental concepts- modulating wave, carrier wave and modulated wave. The modulating wave is the information bearing signal such as human voice or music, audible to the human ear, and intended to be communicated to a receiver. The carrier wave can be transmitted over long distances and is not audible to the human ear. The modulated wave is the wave derived by impressing the information bearing signal on the carrier wave. This wave is transmitted through space to the receiver.

            How is it that the FM transmission provides excellent reception?

            Speech itself is represented by an irregular wave pattern. An FM receiver has to detect frequency changes only; it does not reproduce any amplitude changes caused by electrical interferences. As a result, almost all background noise can be eliminated using filters, producing excellent reception.

            FM transmission is used in radio broadcasting services, multi-channel carrier telephones, communication satellite links, telegraphy, mobile communications, navigational and meteorological equipment as well as for medical diagnostic instrumentation. FM also exhibits channel grabbing that is, if two FM signals are available, the stronger of the two is received and the other is nearly excluded. This permits low-power radio stations operating in the same frequency to operate close to each other. AM transmission does not possess this ability.

What is Multimedia?

            Everyone talks about multimedia these days. What is multimedia? In simple words, multi means many so multimedia would mean more than one kind of media. Computers have invaded energy sphere and have become an integral part of our life today. The field of media is no exception. Multimedia is the outcome of sophisticated blending of various audio and visual communication networks into our desk that produce amazing results.

Multimedia Effect

            Multimedia software combines two or more media for presentation or analysis. It is the result of a co-coordinated work of video, audio and graphics. The old personal computers were Monomedia, as they displayed only one medium. Monomedia computers did not produce sound when they displayed the text on screen. A platform for multimedia emerged with his gradual development in new technology that extended the power and scope of personal computers.

            What specific functions foes multimedia computers perform? A multimedia computer can recreate the sound of musical instruments and can play back recorded sounds and can show pictures and movies on the monitor. It can also access information stored on a computer disc.

            Recorded sounds, movies, pictures and texts have been around for years but multimedia computers can interlink these and produce a combined effect of all these media. It can show animated images and create graphic designs.

            Computer based learning is another gift of multimedia. Learning becomes easier and quicker when the text is supplemented with audio visual aids, and it is for this reason that it has become an effective mod e of education for children as well as adults. The text on the screen is supported by audio instructions and visual aids, which adds to the grasping ability and memory retention by the students.

            All multimedia programmes include six common elements- texts, pictures, movies, animation, sound and increased control. Basing on the nature of interaction wit ht he user, multimedia is divided into two types- non interactive and interactive.

            In non-interactive programme, we receive information presented to us, which are prepared in advance and processed by the computer with little or no intervention by the user. The images, sound and animation etc. are projected form the desktop directly onto a large screen, using a computer projection system or on the computer screen.

            Interactive multimedia is meant for individual use in which the user is in direct communication with the computer, receiving immediate responses to the input data. This type of multimedia usage is very common today.

            Multimedia requires storage of high quality images graphics, texts, animations, sounds, music and video for which high capacity storage medium is required. The use of floppy disks is of no help though they are convenient to distribute. For this reason, multimedia information is usually stored in CD-ROM (Compact disc- Read Only Memory). A CD-ROM can contain up to 700 megabytes of data. For example, the entire Encyclopedia Britannica can be stored in just one CD-ROM.

What are the Different Forms of Energy?

Energy is the basic requirement for doing any kind of work. To the economist, energy is a synonym for fuel, but for a scientist, it is one of the fundamental modes of existence relating to inter convertible of matter.

            It is energy that moves trains or cars, produces light from a bulb, makes rivers flow, etc. energy exists in eight forms- (i) Mechanical Energy (ii) Heat Energy (iii) Light Energy (iv) Electrical Energy (v) Sound Energy (vi) Magnetic Energy (vii) Chemical Energy and (viii) Atomic or Nuclear Energy.

            The law of conservation of energy states that energy can neither be created nor be destroyed. The total energy content of the universe is constant. It means that the total amount of mass energy in the universe or in isolated system forming part of the universe cannot be changed. It can be simply transformed form one form to another.

            Now the question arises- what are the different transformations of energy?

            The motion of trains, buses, cars and scooters involves the change of heat energy into mechanical energy. The chemical energy associated with petrol, diesel or coal changes into heat energy on burning. In an electric bulb, the electrical energy is converted into heat and light energy. When we speak on a telephone, the sound energy changes into electrical energy and at the receiving in to electrical energy and energy transformed into sound energy again. Atomic energy is coveted into electrical energy in a nuclear power plant. Chemical reaction in our body produces heat energy to keep it warm. These are all examples of energy transformation that take place in daily life.

How does Sound Travel?

            Whatever we hear with our ears is called sound. In scientific terms, sound is a kind of disturbance or vibration, which produces sensations in the ears. Like heat and light, sound is also a form of energy. Do you know how sound is produced and how it travels from one place to another?

Sound travels in the form of waves  

            A body produces sound when a part or the whole of it vibrates. When we strike a bell, the vibrations produce sound. If we touch a ringing bell with our hands, we can feel its vibrations. Similarly when a person speaks, the diaphragm in his throat vibrates producing sound. When these waves reach our ears we hear the sound.

            The frequencies of vibrations vary. Our ears are sensitive to sound frequencies ranging between 20 to 20,000 hertz. Human ears cannot perceive frequencies of less than 20 hertz and more than 20,000 hertz.

            Sound travels in the form of waves, which needs a medium to travel. They cannot travel in vacuum. This can be proved by a simple experiment.

            Take a glass bottle and connect it to a vacuum pump. Put a cork on its mouth. Suspend an electric bell inside this bottle. Connect the bell to a battery. It starts ringing and we can hear the sound clearly. Now start removing the air from the bottle with the help of the vacuum pump. As the amount of air in the bottle starts decreasing, the intensity of sound also starts decreasing. When all the air is sucked out of the bottle, we don not hear any sound. This experiment proves that a medium is always necessary for the propagation of sound waves.

            These facts lead to three conclusions. First, vibrations produce sound. Second, sound travels in the form of waves. And third, sound needs a material medium for its propagation. Sound can travel through gases, liquids and solids. It travels fastest in solids, followed by liquids and slowest in gases. It cannot travel in space because there is no material medium. It is for this reason that astronauts talk to each other with the help of radio sets in space.

How does a Screw Jack Work?

            A jack is essential equipment for raising heavy objects off the ground, usually used to remove or adjust wheels of automobiles. Almost all drivers of heavy or light vehicles always carry a screw jack with them in their vehicle, for the simple reason that it alone performs the role of several people in time of emergency. The screw jack is a simple machine like pulleys or levers and is used for raising large loads with a little human effort.

Cross-Section of Screw Jack

            A simple screw jack comprises a thick solid rod in which a screw thread has been cut, a base plate in which it can rotate, and a block or nut through which the screw threads run. The block is shaped in such a manner that it hooks on to the underside of the car. When the screw is rotated with the help of Tommy bar, which passes through a hole in the screw, the block is slowly raised or lowered.

            A screw thread is a spiral cut made in the rod so that the screw may be regarded as a spiral inclined plane. For each complete turn of the screw, it advances by a distance equal to the pitch of the screw. Pitch of the screw is the distance between any tow adjacent ridges of the thread. The screw of a screw jack whose diameter is ¾ inch may have six threads per inch, so the pitch of the thread is 1/6 inch. Thus, for every one complete revolution of the Tommy bar, the lifting block moves 1/6 of an inch up or down.

            The velocity ratio of any machine is found by dividing the distance ‘e’ through which the effort moves by the distance ‘I’ through which the load is raised. If the Tommy bar is a little more than 6 inches in length then it will trace out a circle of radius of 6 inches for each complete revolution. The circumference of this circle is about 37.7 inches so that the load is raised by 1/6 inch for every 37.7 inches that the effort moves.

            Even if the thread of the screw is kept clean and well greased, there is still likely to be considerable friction between the screw and the lifting block as well as the base plate. Thus a load of 225 kilograms, which is the weight, supported by one of the four wheels of an average family car; it could be lifted by a 1.25 kilograms effort if there were no friction. But in practice, the effort would be between 3.4 kilograms to 4.5 kilograms. In other words, it is an ideal machine, which requires no energy to move its component parts, as the velocity ratio is equal to the mechanical advantage.

            On account of the large frictional forces between the screw and the block the load cannot unscrew it self and run back under its own weight.

How does a Battery Torch Work?

            A battery torch is a portable electrical appliance used for lighting. Doctors use it to examine closely the ears, eyes, noses and mouths of the patients. We use it to move around in the dark, while other light up areas to search. But do you know how a torch produces light? A battery torch can be divided into four main parts- the battery, bulb, causing and the switch.

Parts of a Battery Torch

            The battery is in the form of dry cells. Dry battery cells such as those in torches, transistors or calculators produce electricity only for a limited time. Most of the torches make use for two or three dry cells. The bulb has a coil, which gets heated up and emits light, when the current is passed through it. The body of the torch holds the battery bulb and the switch. The switch helps to regulate the flow of current. When the switch is pressed, the cells get connected to the bulb, and the bulb emits light.

            The torch produces light when the positive and negative terminals of the dry cells are connected to the bulb. The current passes from the positive terminal through the bulb and returns back via the negative terminal, thus making a complete circuit. When the switch is moved to the on position, a metal piece inside the case touches the positive terminal of the battery, and the circuit is completed.

            In a battery torch, a reflector is placed behind the bulb, which reflects the light over a long distance.

What is an Electronic Mail?

            Electronic mail is a modern method of instant delivery of mail without the involvement of a postman or post office. In this system of mailing messages are sent with the help of a computer.

The Network by which E-Mails are sent

            In electronic mail system, a letter or a document is typed and edited on a computer. It is then set to the addressee through a computer network in the form of electrical data. The receiver could be anywhere, but he should also have a computer and an electronic mail system, the contents of the transmitted letters or documents get displayed on the computer screen of the addressee.

            If the addressee is not available at his computer, the message is automatically stored in the computer’s memory. When he returns, the computer gives an indication that a mail has arrived. If he desires, he can get a printout of the message.

            With the help of an electronic mail system, both typed and handwritten messages can be transmitted. Electronic mail is swift and saves time and paper work. It needs a telephone or a satellite, or a cable links for visual, voice and data transmission. This system is prevalent in developed countries but spreading fast throughout the world. E- Mail is widely sued in internet services. It is also connected to mobiles, laptops and palmtops.

How does a Currency Counting Machine Work?

            If you have lately visited a bank, you must have noticed that the currency notes are counted by a machine instead of the counter clerk. Almost all banks in the world now use currency counting machines for counting and packing notes in denominations of hundreds. Job of counting and packing is done manually by a large number of people, which is a boring and tiring job. To eradicate this problem, scientists have developed a machine, which automatically counts and packs currency notes.

Currency Counting Machine 

            The bundle of notes to be counted is placed o platform P-1. A feeding roller R-1 pushes these notes forward. A sensor S-1 counts these notes. Thereafter, the notes pass through the rollers R-2 and R-3, and channel C-1. Through the channel, the notes reach the sensor S-2. In case of any error in counting, S-2 will shut the motor automatically and display the error. After sensor S-2, rollers R-4 and R-5 pick up the notes and throw them into the slots of the centrifuge roller. These notes are released as they reach the platform P-2 and start stacking upon it. This platform is equipped with another sensor S-3 that indicates whether P-2 is empty or loaded.

            Currency counting machine is a microprocessor-based machine and hence its reliability is very high. Similar machines can count currency notes and coins. These are portable machines and can be installed anywhere.

What is Internet?

            There is hardly anyone who lives in a city and has not heard of internet or used it. It is a fantastic means of communication, education and research. Rapid progress made in the field of information technology has revolutionized the world of communication. The world is gradually shrinking and becoming a global village. Interaction between people of all the countries has become more frequent than ever before. The widespread and effective use of computers in the field of telecommunications has made the world a smaller place to live in.


            ISD, FAX, Electronic Mail, Paging Service and now internet- all are the gifts of this revolution. Internet has aroused much interest in recent days, as it has become a very powerful medium of communication. But what is internet and how does it operate?

            Internet is the world’s largest computer network. A computer network is basically a bunch of computers connected together by some means, usually telephone links. It is just like a radio or TV networks that can link various radio or TV stations so that they can share a common programmed. The major difference is that in a TV network is that it is one-way communication, and the same information or programmed is sent to all stations.

            In a computer network, a message is usually routed to a particular computer. Some computer networks have a central computer and a group of remote computers that are linked to it- for example, the centralized railways reservation system links many terminal counters to a centralized computer.

            In internet, any computer on the network can communicate with any other computer. Truly speaking, the internet is not really a network; it is a network of networks- all freely exchanging information.

            Through internet, people from all countries can now share information, ideas, stories, data and opinions- the functions that were carried out by letters, telephones and other modes of communication so far. It has become the fastest and most reliable way to exchange information.

            For example, during the 1991 soviet present day Russia coup, a tiny internet network provided all the information to the rest of the world, when all other communication systems were closed. Medical researchers all over the world use the internet to establish and maintain databases of rapidly changing data.

            The internet facilities are provided through a large number of servers. Listing all the services would make the list exhaustive. For example, electronic mail is the most widely used internet service. Electronic discussions and communicate with people over the net. Online chat, information retrieval, bulletin boards, games and gossips challenging other players who can be any where in the world is some other kind of internet services that are available.

            India’s access to the internet has ushered in a new phase of computer communication in the country. Originating as a small electronic community in the American defense department as a way for military researchers to contact each other, internet is now the world’s largest electronic network.

What is a Silicon Chip?

            The microchip or silicon chip has completely changed the electronic world by providing a new direction to it. It has led to the invention of electronic calculators, personal computers, digital watches, microwave oven, etc.

Peltier Effect Thermoelectric Device

            Silicon chips are tiny crystal of silicon, which contain large number of electronic components. Silicon is the most abundant element found on the earth’s crust. But silicon is not found in a free state in nature.

            The size of a chip is smaller than our fingertips. In 1 square centimeter chip, one million electronic components can be inserted. They have very small electrical circuits, called microcircuits. These are used in transistor radios, digital watches, calculators, and computers. They can be used in miniature electronic devices, as the chips are very small.

            But how is silicon chips made? Silicon chips are made form a single crystal of silicon. Thin wafers of about 0.5 millimeter thick are sliced from a single crystal. One side of each wafer is first polished and then oxidized in a furnace. The disc is covered with a layer of photo resist material and then exposed to ultraviolet light through the clear sections of a mask. A light sensitive coating is applied and the solvent dissolves the exposed areas. Unexposed areas are not affected, so a pattern identical to the mask remains. The exposed areas are etched in hydrofluoric acid. Another solvent removes the resistance.

            Next, the wafer is exposed to chemicals in a furnace, which penetrate the silicon through the oxide gap to make transistors. The process is repeated several times. The wafer is coated with aluminum and a final layer is metals connect the components together. After careful inspection, chips are selected and released for use.

            Today microchips are being used in electronic sewing machines, washing machines, word processors, and so on.