Category How does It works, How things work, How is it done, Curiosity

All computers work in basically the same way. They follow a set of instructions called a program that enables them to do calculations on information fed into them.

This process produces a result that is used in some way. The great advantage of computers over other machines is that the program can be changed, so that a computer can be given a wide variety of tasks to perform.

Computers consist of four main units – an input unit, a central processing unit is at the centre of operations and generally consists of a microchip located in the computer case. It controls the operations of all other units, which may be part of the computer or connected to it.

The input unit is used to feed information or data into the computer. It is usually a keyboard, but it may also be a light pen that interacts with a computer screen, or simpler devices such as a joystick, a mouse or a bar-code reader. The keyboard is also used to write programs.

The central processing unit first passes the information to the internal memory, where it is held temporarily. The program is also held in the memory, and the processing unit follows the program to produce the results. These go to the output unit, which is usually a video screen or printer, or they may be sent along telephone lines to other computers.

The computer also has an external memory unit such as disc drive that takes programs and data from the internal memory and records them for use at a later date.

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We have all at one time or another heard the echo of our own voice. An echo is caused by sound waves being bounced back from a solid obstacle, rather like a rubber ball bouncing off a wall. The same thing happens to radio waves which are sent out by a powerful transmitter. When the waves collide with a solid object they bounce back and can be picked up by a receiving set which is usually located at the same place as the transmitter. Since the speed of these waves is known we can tell how far away the obstacle is by calculating how long the waves take to cover the distance. This is how radar works.

The word ‘radar’ is an abbreviated form of the name ‘radio detection and ranging’. Radar is now used everywhere’ at airports, missile bases, space centers for following and tracking satellites and on ships and tracking satellites and on ships and aircraft for automatic navigation. A simple form of radar is used by police to detect speeding vehicles.

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You may have seen a certain type of lawn sprinkler which works by spinning round and round as the water squirts from it. The spinning movement is caused by the pressure of the water pushing against the movable arm of the sprinkler.

Sir Isaac Newton noticed something like this happening and it led him to discover an important law of nature. Newton’s law was that for every action in one direction there is an equal action in an opposite direction. In the case of the lawn sprinkler the water goes in and pushes in one direction and the sprinkler turns in the opposite direction.

The same law explains why a rifle recoils sharply when it is fired. The firing of the gun is known as the action and the recoil of the gun is the reaction.

The principle is what makes rockets speed through the air. Rockets are fuelled by very highly compressed gases. When these gases are violently released from the tail of the rocket the reaction they set up gives the rocket a mighty push in the direction opposite to the gas flow.

The greater the distance to be travelled, the greater must be the initial thrust. When Saturn V was launched, for example, its five engines consumed kerosene and liquid-oxygen at rate of 15 tons per second.

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It was far more difficult for man to discover how to produce artificial cold than it was for man to discover how to produce artificial cold than it was for him to produce warmth.

In olden days man tried to keep things cool during the summer by using snow or ice. This was a very difficult process. The snow and ice had to be carried down from the high mountain tops and stored in specially built places.

The ancient Romans, for example, brought their snow and ice from the Apennine Mountains. They dug large chambers in the ground which they called officinae reponendae nivis. This meant snow store. The store was covered in wooden boards and the ice was brought to the towns from the Apennine region near Rome and in Sicily from Mount Etna.

The first Experiments to produce ice artificially began in the seventeenth century. It was later discovered that in specified condition certain substances changed from a solid into liquid state. This fusion, or melting process, was found to be caused through the absorption of heat by those substances. As the heat was absorbed it was accompanied by a steady cooling of the temperature. Further experiments showed that the same absorption of heat could be carried out by evaporating and liquid. An example of this is when a sudden breeze evaporates the perspiration from our faces and makes us feel quite chilly. It is on this principle of heat absorption that ordinary household refrigerators work. The most commonly used liquid to bring about cooling is ammonia gas in solution. This solution runs through coiled tubes. It starts as a liquid and through compression becomes a gas which absorbs the surrounding warmth. This process is repeated over and over again until ice begins to form.

The first household refrigerator was made early in the nineteenth century. Since 1918 their use has becomes more and more widespread.

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In 1831 the Belgian physicist Joseph Plateau produced an apparatus which he called the phenakistoscope. This was followed by other devices such as the zoetrope or ‘wheel of life’ of the British inventor William Horner in 1834 and praxinoscope of the Frenchman Emile Reynaud in 1880. Despite their difficult names these apparatuses were all fairly simple and they all exploited a certain characteristic of the human eye.

If an object is placed before our eye its image is picked up by the retina, an extremely sensitive screen inside the eyeball. Every change of object outside causes a change in the image received by the retina and if the changes are rapid enough a whole line of images can blend into one. In the phenakistoscope and the other machines a series of image showing the various stages of a person in movements were shown on a revolving drum. All the images ran together and the viewer received the impression of continuous movement. Modern animated cartoons are also produced by rapid succession of drawings.

An important development in motion pictures took place in 1889 when the famous American inventor Thomas Edison, succeeded in using photographs instead of drawings. The photographs were taken one after the other on one roll of film. Edison then invented the Kinetoscope to show his moving pictures. This was kind of peep-show device which showed viewer about fifteen seconds of life-like movements.

The first truly modern cinematographic machine was produced in 1895. In that year the brothers Auguste and Louis Lumiere of France patented their famous and historic ‘cinematograph’.

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A camera is a fairly simple piece of equipment in its basic structure. One must not be put off by the numerous levers, buttons, scales and other gadgets on the outsides. These are all extremely useful aids but are not completely essential.

The essential part of the machine is what gives its name: the camera obscura. This is Latin for dark room. Photographs are produced when rays of lights penetrate into this dark chamber. The light must enter through a small opening and strike against a sensitive film. The surface of the film is covered in an emulsion of chemicals which capture the images being carried by light rays. The small opening, or aperture, must also be able to open the aperture to let the light in. this mechanism is called the shutter. In a simple camera this is about the only moving part.

In more expensive cameras the fitting includes mechanism which can vary the exposure time which determines how long the shutter will stay open. The can range from a thousandth of a second for fast-moving subjects to one second or more for still dimly-lit scenes. Other controls include an aperture selector to vary the amount of light passing through the lens, and a focusing mechanism to produce a sharp image.

The camera obscura has long been known to man and Leonardo da Vinci made accurate drawings of it in the fifteenth century. It was not until 1839, however, that the first commercially available cameras were made in Paris by Alphonse Giroux for Daguerre.

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When the first railway began to operate it was suggested that a messenger should ride on a horse ahead of the train to tell people of its approach and warn the engine driver of any obstacles along the track.

Soon the train was able to travel much faster than the horse. Men with flags stood beside the track and either signaled the train-driver to stop or waved him on.

The problem of travel safety grew as trains increased in speed and numbers and level crossing with gates were built as well as viaducts to take trains over dangerous or difficult places.

Eventually a comprehensive system of mechanical signaling was evolved. Semaphore signals that swung up or down on a tall pole beside the track were the most common. Nowadays the majority of large railway stations have colour-lights signals, with red meaning ‘stop’ , green ‘go’ and amber ‘caution’.

All these signals are now worked electrically. It is no longer necessary for a man with a watch to check the various times when trains pass, open gates or decides which track the train will go on to and make a note of trains which have been delayed. Today all these tasks are done by computers and the signal posts of large stations are completely automated.

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Sometimes films are shots or photographed without sound: the dialogue is added later together with sound effects and other noises. When these sounds are added the noise of a waterfall might be produced by merely shaking water about in a basin or the voice of a stage actor might replace that of the film actor in a process known as dubbing.

The major developments in cinematography were the introduction of sound in 1927 and the advent of colour photography.

The cinema really grew up as an art after the Second World War but it found an extremely dangerous rival in television. So the film industry began to think up counter attraction. These included the evolution of wide screens as in the processes known as Cinema Scope and Cinerama. In wide-screen presentations, a special lens may be used that spread out the image on the film to fill the screen. When the film is shot, a similar kind of lens is used to squeeze a wide field of view on to standard film. Modern cinemas in addition may also use stereophonic sound which is emitted by numerous loudspeakers. This gives the audience the impression that they are might in the middle of what is happening.

The story of the cinema is not yet finished. Scientists are studying a way of producing satisfactory three-dimensional films so that the images are no longer flat. Experimental have also been carried out with a circular screen that completely surrounds the audience.

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The first step towards making a film is the idea for the subject. The next requirement is money to pay for all the production costs. The producer is the man who raises this money and generally he chooses the director, the most important man in making a film. The director then appoints a writer to prepare a screenplay which is like a stage play but consists of hundreds of short scenes which finally make up the whole film.

A film studio seen for the first time is quite an overwhelming sight. You may see a straight road lined with marble columns representing a roman road of 2000 years ago. Near this scene there might be a ramshackle prairie town of the Wild West. In another part of the studio there may be a magnificent governor’s palace set in imperial India. The studio is therefore crowded with Roman soldiers or gladiators, cowboys or young English colonial ladies. Some part of the studio will probably be very strictly cordoned off because a film crew may be ‘shooting’ there.

Today film directors prefer to work on location which means they film their scenes in real places outsides instead of creating them from plaster and wood inside a studio. Other film crews with their actors and actresses travel from one continent to another. But when a film is historical or period piece it is usually shot inside a studio. Films employ armies of technicians. Skilful carpenters and scene painters build intricate structures known as sets which can be of medieval castles, or of ultramodern apartments.

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Modern science and technology have made it possible, among other wonderful things, to make a permanent record of sounds and human speech. The tape in a tape recorder is made of an insulation material on which a thin magnetic layer has been placed. The tape is normally 3 millimeters wide in cassettes and 6 millimeters in reels. How does a tape recorder work?

There is a motor which turns a reel of tape from the supply wheel to the take-up reel. The tape passes across the recording head. When we speak into the microphone the voice is turned into a series of electrical impulses. These impulses are caught on the tape in various patterns. In video tape recordings the light signals are turned into electrical impulses recorded on the tape.

When the tape is played back it runs past an electromagnet. The magnetic patterns that have been recorded along the magnetized tape set up a variable magnetic field with the electromagnet.

The impulses of this magnetic field are the converted into sounds which are amplified and played through a loudspeaker to re-emerge as the original speech or music that was first fed into the tape recorder.

Today tape recorders are very popular. Besides being easy to operate they have the added advantage that recordings can be erased and the tape used many times. A new compact type of tape recorder is the cassette recorder. The works on the same principle but use narrower tape in its own self-contained cassette.

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 Even air has weight and, like any solid object, it presses down on the surface of the Earth. Scientists decided to measure the amount of his pressure and the Italian Galileo was the first to succeed. He used a very long tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 meters. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water; mercury. The mercury rose inside its tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 metres. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water: mercury. The apparatus was given the name barometer from, the Greek baros meaning ‘weight’ and metron meaning ‘measure’. Torricelli soon noticed that the height of the mercury column varied with changes in air pressure. About 1647 Blaise Pascal’s experiments finally convinced people of the correctness of Torricelli’s ideas.

The most modern form of this instrument is the aneroid barometer, from Greek a meaning ‘without’ and neros meaning ‘liquid’. The aneroid barometer consists of a small steel box which contains a vacuum. The pressure of the air outside the box can cause the surface of the box to move in or out. A needle on the dial records the movements of the box along a graduated scale to show the changes in air pressure.

This type of barometer is smaller and more portable than a mercury barometer but it is not quite as accurate. It has first to be calibrated or set to a mercury barometer before it can be used.

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Be a Travel Agent

Part of a travel agent’s job is to create an itinerary which is a route for your journey. Imagine that you are a travel agent planning a trip for yourself and a friend to an exciting place.

You Will Need:

• white paper a stapler
• newspapers and magazines that an adult has given you permission to cut up
• scissors
• crayons or felt-tipped pens

What To Do:

1. Decide how many days you and your friend would like to travel Then staple several sheets of paper together to make a short booklet. Allow two pages for each day of your trip,

2. Look through newspapers and magazines or print out photos from the Internet. Cut out pictures of interesting places, such as museums, monuments, amusement parks, zoos, and nature parks, that you would like to visit. Remember, you’re not really travelling, so anything goes! Also cut out pictures of hotels, motels, camping grounds, and restaurants where you would enjoy staying and eating.

3. Now arrange your pictures so that you have two or three places to visit, one place to stay, and two or three restaurants for each day of your holiday.

4. Glue the pictures into your booklet. You might want to put numbers by each picture to show what you would do first second, and so on. You also could put the words breakfast, lunch, and dinner next to the restaurants to show where you would eat each meal.

Now you are ready to present the “itinerary” to your friend. “Bon Voyage!” This is French for “have a good trip!”

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Terrific travellers are clever and ready for new sights, new sounds, new tastes, and new experiences. They respect other people’s languages, customs, and foods, even though they might seem strange at first. Terrific travellers expect surprises, and they know that each journey is a chance to learn something new.

Take this quiz to find out if you are a terrific traveller. You can pick more than one letter for each number. Then count the number of a’s, b’s, c’s, and d’s you score.

1. You are taking a stroll down a wooded path. You spot a flower you’ve never seen before. You:

a. pick the flower so no one else will find it.

b. ignore the flower. Woods are boring!

c. look up the flower in your nature guide and make a sketch of it in your notebook.

d. have a contest to see how many unusual flowers you can find.

2. It is late afternoon in a Spanish village. All the shops and restaurants are closed for siesta. You:

a. bang on the windows and tell everyone to wake up because you are hungry

b. pout in your hotel room.

c. use the time to read about local customs.

d. have a picnic in the park with the snacks

you packed in your backpack.

3. It is your only day to go to the beach. Suddenly, it starts to rain. You:

a. tell everyone that your trip is ruined and you want to go home.

b. sit in your room all day and watch it rain.

c. use the time to write postcards to your friends.

d. go to a museum you hadn’t planned to visit.

4. You are in a restaurant and the waiter brings you an odd-looking dish you’ve never had before. You:

a. pinch your nose and yell “Ugh!”

b. push the plate away from you when no one is looking.

c. ask the waiter to tell you the name of the dish and how to pronounce it.

d. try the dish even though you don’t know whether you will like it.

5. Your parents tell you that you are going to an art museum instead of the amusement park. You:

a. plan to bring your in-line skates so you can play tag with your sister.

b. sigh loudly and dawdle behind your parents once you get there.

c. take the museum tour and learn about the paintings.

d. go on an art museum treasure hunt.

What Your Score Means:

Mostly A’s:

Tourist, go home! You won’t enjoy your trip, and you may keep other people from enjoying theirs.

Mostly B’s:

B is for boring. You need to put more effort into your travels if you want to have fun!

Mostly C’s:

Your willingness to learn about the places you visit makes you a terrific traveller.

Mostly D’s:

You’re terrific, too. Your adventurous spirit guarantees that you will have fun wherever you go.

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Draw a Map to Scale

You don’t need rulers or tape measures to draw a map to scale. Make different maps of your own room-using just your feet!

You Will Need:

• graph paper
• crayons or felt-tipped pens
• a ruler

What To Do:

1. Select two things in your room, such as your dresser and bed, or the door and the window.

2. Estimate, or guess, the distance between the two objects you have chosen.

3. Now use steps to measure the distance. Walk in a straight line, placing your feet from heel to toe. Count how many steps it takes to get from one object to the other. Write down that measurement.

4. Decide on a scale, such as the length of one square of graph paper equals one step Draw a map of your room using the measurements (in steps) you just took. Use your scale to show the distance between the two things you chose. At the top or bottom of the map, mark the map scale.

5. Now draw more maps to different scales. For example, one step equals two squares.

6. Give each of your maps a title, such as “first map”. “second map”, and “third map”.

Now you are ready to compare your maps. How are they alike? How are they different?

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One way to help your friend find your house quickly and easily is to draw a map. It’s easy to make a map of your neighbourhood, and its fun too

You Will Need:

• plain white paper
• pencils
• a ruler
• crayons or felt-tipped pens
• tracing paper

What to Do:

1. First, walk around your neighbourhood and make a list of the things you want to show on your map. You may want to ask an adult to help you. You might want to show your house, a friend’s house, the park, or your school. Think about where places are, how far apart they are, and what shape they are. As you walk, write down the names of the streets in the order in which you get to them. Which buildings and streets would help someone find your house?

2. Next, draw your map. Draw the streets in pencil and show where they cross. Print the name of each street on your map.

Then add shapes that stand for your friend’s house, a postbox, or a shop. You might also need to add streets that aren’t on the map. Label each street. Then add labels for important places such as your home and school.

3. Now colour your map. Use different colours for such areas as houses, streets, and parks. At the bottom of the map, list what each colour stands for.

To find out whether your map works, let a friend use it to try to find your house or another place on your map.

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What House Will You Build?

Here is your chance to design your own house.

Where You Live

1. An area close to a swamp. Floods occur quite often.

2.A very rainy place.

3.A dry rural place with few trees.

4.A crowded big city with buildings that are homes for many people.

5.A place close to a river, lake, sea, or ocean.

Materials for a House

A. mud for making bricks

B. wooden poles on which to build your house

C. waterproof tiles for your roof

D. concrete bricks and steel beams

E. wood, fibreglass, or aluminium for making a house that floats

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Weave Your Own Friendship Bracelet

In many countries, people make rugs, baskets, and blankets. They make them by weaving, Weavers use a machine called a loom to cross threads over and under one another. The threads are made of cotton, silk, or even grass. Sometimes the threads are coloured with dyes made from plants. You can make a simple hand loom out of straws and use it to weave a bracelet for your friend.

You Will Need:

• 1 metre thin cotton thread
• 2 plastic drinking straws, each cut in half
• different-coloured yarn

What To Do:

1. Cut the thread into four equal pieces and pass each piece through a straw. Tie the four ends above the straws into a knot.

2. Knot the other end of each piece of thread.

3.Tie a piece of yarn to the thread just below the top knot.

4.Weave the yarn under and over the straws from side to side. Use your fingers to push up each row of yarn onto the thread and slide the straws down. To change colours, tie a new piece of yarn to the end of the first one and weave in the loose ends.

5. Make your bracelet long enough to tie around your friend’s wrist. When your bracelet is the length you want, remove the straws. To fasten the last row, tie the end of the yarn to the piece of the thread. Then tie a knot with the two pieces of thread on the left. Repeat with the pair on the right. Finally, tie together the four thread pieces with another knot.

Now you are ready to give your bracelet to a friend!

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Make Your Own Continent Map

Just as you can learn a lot about a place by looking at a map, you can learn a lot by making your own map. Choose a continent in this chapter that you would like to learn more about, and map it!

You Will Need:

• books or encyclopaedia articles about your favourite continent
• a pencil
• a large sheet of paper crayons or felt-tipped pens

What To Do:

1. Read about the continent and answer the following questions: What is the tallest mountain? What is the longest river? What is the largest lake or desert What animals live there? What are the biggest cities?

2. Look through encyclopaedias and other books to find different maps of your continent. How do these maps show important information, such as the locations of mountains, rivers, and large cities?

3. Trace or copy the outline of the continent onto the large sheet of paper.

4. Now use a pencil to fill in the map outline. Choose symbols to show cities, rivers, mountains, deserts, and the animals that live in different places on the continent.

5. Colour your map. Use green for land, blue for water, and brown for mountains.

6. Decorate the border of your map with pictures of the continent’s people, animals, and any other features you want to show.

Now, laminate your map or put it in a plastic cover.

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Although the helicopter in its present form is scarcely 50 years old, the principle of the rotary wing has been known for centuries. The Chinese used it some 2500 years ago for their flying top — a stick with propeller-like blades on top which was spun into the air. And Leonardo da Vinci actually sketched a helicopter in 1483. The English flight pioneer Sir George Cayley was among several people to design a model helicopter in the late 1700s, but the first man-carrying helicopter, which rose a few feet in the air, was not built until 1907 — by a Frenchman, Paul Cornu, at Lisieux. Problems with stability and other design aspects led to helicopters being abandoned for nearly 30 years in favour of fixed-wing aircraft. Many of the design problems were, however, solved by the Spanish inventor of the autogiro, Don Juan de la Cierva, in 1919. This aircraft had a large rotor that was not driven by the engine but turned freely in the airflow. It could not take off vertically — it had to taxi to get the rotor turning enough to lift it.

Not until 1936 did the German Professor Heinrich Focke, of the Focke-Wulf Company, design a practical helicopter with twin rotors. Three years later a Russian-born engineer, Igor Sikorsky, produced a successful single-rotor helicopter, the VS-300, in the USA. This was the true ancestor of the modern rotorcraft — the most versatile of aircraft.

The development of jet engines in the 1950s led to the adoption of turboshaft engines that have considerably increased the range and speeds possible. Today the helicopter is invaluable not only as a military transport, hedge-hopping patrol plane and sky crane — for lifting steeples onto churches, for example — but also for rescuing people from remote mountainsides, sinking ships and burning buildings.

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Submarines often travel in the ocean depths for weeks on end. They do not need to surface to check their position by the Sun, Moon or stars, because the latest navigation systems allow them to know where they are to within less than 320ft (100m) of their actual position while still submerged.

 These systems are known as inertial navigation systems and are computer-controlled. There are usually at least two on a submarine, operating independently. They are a modern version of ‘dead reckoning’ — calculating where you are by measuring exactly how far you have come from your starting point, and in what direction.

The inertial navigation system is held absolutely horizontal and pointing in a fixed direction by gyroscopes, whatever the attitude of the submarine.

 At the start of the voyage, the instruments are fed with the submarine’s exact position. An accelerometer then measures movement in every direction, and the computer works out the overall distance and direction travelled, thus establishing the present position.

Sonar is used to determine the water depth below the vessel to prevent it running aground. Inertial systems are on the whole accurate, but the small errors they do make gradually accumulate. They have to be realigned regularly. This is done by picking up radio signals from satellites in space, which form part of the American NAV-STAR Global Positioning System (GPS). The submarine has to partly surface.

 The satellites transmit a radio message which contains precise details about their orbit, and a time signal controlled by an atomic clock. In effect, the signal says ‘It is now time X’. The submarine uses its own clock to calculate how long it takes the signal to arrive. As radio waves travel at 186,000 miles (300,000km) per second, the navigators can calculate the sub-marine’s distance from the satellite by the time the signal takes. By calculating the distance from three GPS satellites, the ship’s position can be pinpointed on a chart.

During the 1990s, the last 04 18 satellites in the GPS system will be placed in orbit at a height of 12,500 miles ,20.000km), orbiting the Earth at 12-hourly intervals. They will ensure that at any time at least four satellites will be available for navigators to calculate their position to within 550yds (500m;

The GPS system has virtually replaced older forms of submarine navigation such as the OMEGA system, but submarines still carry it as a back-up. This system detects radio signals broadcast from eight stations dotted around the Earth’s surface — in Japan. Hawaii, Australia, Argentina, North Dakota. Norway. Liberia and Reunion Island. These stations broadcast at very long wavelengths, so their signals carry all around the world. The signals are synchronised, and by measuring the time differences in their reception, a sub-marine’s position can be estimated to within about miles (3.2km)

 Inertial navigation also mounted in long-range intercontinental launched from submarines .

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Medieval castles had all sorts of traps pitfalls to keep out intruders. Homes of today can have an equal number of defences, without having to resort boiling pitch. Modern defence devices include floodlights or alarms that are triggered when an intruder upsets a circuit monitored by hidden magnets or micro. chips, or by invisible beams.

The outer defences

The modern burglar might first have to face  a strategically placed invisible infrared detector that is affected by temperature changes caused by body heat. When anyone approaches the house, a sensor in When the detector switches on floodlights. If the caller is legitimate, the lights show the Way but anyone planning burglary will feel very exposed and less likely to continue.

The sensor is pyroelectric — that is, made from a ceramic material such as tourmaline, which, when heated, generates a voltage across it. The system is designed so that the sensor will respond to a temperature change caused by human body heat, but is less likely to be set off by changes in the weather.

 A burglar who dodges a floodlight – barrier may then face a door connected to a noisy alarm. A magnetic switch IL inserted between the door and its frame. When the door is shut, two contacts keep switch circuit closed. This switch is monitored electronically by an alarm circuit. If the door is opened arid switch circuit is broken, the alarm circuit triggers the alarm.

But a resolute burglar, out of sight of passers-by, might attack the door with a chisel or drill. This type of attack can be foiled by a vibration detector fitted to the door. This is a device in which a ball is disturbed by vibrations. The ball rests on sharp metal points wired to a microchip that is programmed to accept certain vibrations — such as those caused by wind or passing traffic — as normal. If the ball bouncing on the points sets up vibrations not in the program, it sets off the alarm.

The inner defences

If the burglar succeeds in getting through a door or window, he may face a battery of inner defences. These include pressure Dads concealed under the carpet and inked to an alarm circuit. They have two metal plates or foil sheets separated by a layer of spongy plastic. The two plates are pressed together if anyone treads on them, and this sets off the alarm.

Anyone who prowls around inside the house may be caught by a ‘magic eye’. This is a photoelectric cell with an invisible infrared beam shining onto it. If the beam is interrupted, the photocell triggers an alarm.

Other types of indoor detector use either ultrasonic waves (too high pitched for humans to hear) or microwaves (high-frequency radio waves) transmitted by

devices called transducers. They transmit the waves at a certain frequency (a given number per second), and the waves are reflected back to the unit from objects in the room. If anyone moves through the room, the reflected waves get bunched up or pulled apart, so their frequency is altered. The sensor detects the frequency change and feeds signals to a microchip which assesses the speed and bulk of the intruder. Anything assessed as typically man-sized makes it set off the alarm.

A commoner type of indoor detector uses an infrared system similar to the outdoor floodlight type. in the detector. a many-faced mirror or special lens creates a number of sensitive zones. If anything moving in and out of these zones is at a different temperature to the room surroundings, it generates a voltage. The detector electronically monitors the voltage, and is designed to set off the alarm if the temperature increase is likely to be caused by human body heat.

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When lightning struck the roof of York Minster, one of Britain’s finest medieval cathedrals, in 1984, it started a fire that was if trapped between the ceiling and the wooden roof. Firefighters could not get into the area, and the enormous heat that built up destroyed most of the roof.

If lightning should strike York Minster twice, space-age science has ensured that the same type of damage will not happen again. The new roof is fitted with trap doors to let the heat out and the firefighters in, and the doors have latches operated by springs made from memory metals, which will open automatically if they get hot.

Memory metals have two different shapes they can ‘remember’, and will switch from one to the other under certain conditions. The York Minster trap-door springs are made to remember a certain temperature, at which they will expand and withdraw the bolt, releasing the door.

One of the first uses of memory metals has been for hydraulic pipe couplings in aircraft, which came into use in 1971. The couplings are made too small to fit at a certain temperature, and are then cooled to well below room temperature and stretched to fit. When they warm up to their normal operating temperature, they shrink to the first shape, forming a tight joint. The same idea is used in surgery, with metal couplings to bind together broken bones. Body heat keeps them constantly tight.

Metals that change their shape under heat now have all kinds of uses, such as operating switches and valves in automatic coffee machines, and opening greenhouse windows when it is hot and closing them when it is cold. Most metals are made up of crystals (arrangements of atoms). When two or more metals are combined into an alloy, the alloy can form different crystal structures under different conditions.

Some alloys, if they are cooled rapidly, will undergo an abrupt change to a different alignment of crystals at a certain temperature. This transition temperature varies with the make-up of the alloy. The changed structure it brings about is called martensite, after the German metallurgist Adolph Martens who first identified it.

If such an alloy is shaped by heat treatment so that it becomes martensite at, for example, 122°F (50°C), it will change its shape at that martensitic temperature, but revert again at a different temperature.

Shaped for shaping

A Japanese company has found an unusual use for memory metals — as a super-elastic wire frame in brassieres. The alloys used will stretch up to ten times more than ordinary metals. When stretched in use, the bra wire gradually returns to its original bust-supporting shape.

Another use for super-elastic wire is in straightening teeth. Conventional stain-less-steel wires have to be regularly tightened, often by turning a tiny key. Super-elastic alloy wires exert a continuous gentle pressure ideal for coaxing teeth in the right direction.

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When someone blows into a breathalyzer bag, any alcohol in their breath is turned into acetic acid (vinegar). This chemical reaction changes the colour of the crystals in the blowing tube. The more crystals that change colour, the more alcohol they have in the body.

The first breathalyzer was developed by an American doctor, Rolla N. Harger (he called it a ‘Drunkometer’), and it was introduced by the Indianapolis police in 1939. Similar breathalyzers began to be widely used by the police in many Countries in the 1960s, as a yardstick for judging a driver’s ability to drive. A high Intake of alcohol dulls the nervous system and slows up coordination.

To begin with, the commonest type of breathalyzer was a plastic bag, similar to a balloon, with the crystals in the blowing tube. and the driver was asked to inflate the

bag. If the crystals changed colour as far as a level marked on the tube, the driver was possibly ‘over the limit’, and needed further tests. The crystals used were an orange-yellow mixture of sulphuric acid and potassium dichromate. They turned the alcohol into acetic acid (vinegar), and in doing so they were changed into colourless potassium sulphate and blue-green chromium sulphate.

The breathalyzers used by the police today, however, are usually electronic, and much more accurate than the inflatable-bag type. They use the alcohol blown in through the tube as fuel to produce electric current. The more alcohol the breath contains, the stronger the current. If it lights up a green light, the driver is below the legal limit and has passed the test. An amber light means the alcohol level is near the limit, a red light above the limit, and in both cases  the driver has failed the breath test and needs further testing.

This type of breathalyzer is about the size of a TV remote control, and contains a fuel cell that works like a battery. Breath from the tube is drawn into the cell through a valve, and meets a platinum anode (a positive plate). which is against a spongy disc impregnated with sulphuric acid. The platinum causes any alcohol in the breath to oxidise into acetic acid — that is, its molecules lose some of their electrons. This sets up an electric current through the disc, and it flows to a cathode (a negative plate) on the other side.

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Most drivers have experienced the frightening moment when the wheels lock and the car slides uncontrollably toward the vehicle in front. Although drivers ate taught to leave a sufficient gap for braking, and to take extra care on wet or icy roads, the huge number of rear-end collisions every year is ample evidence they do not.

Skidding and sliding happen because the behaviour of a car changes rapidly when the wheels begin to lock. Up to a point, pressing the brake pedal harder produces greater deceleration. But once the wheels have locked, their grip on the road is lost, they begin to slide instead of turn, and the driver can no longer control the car’s direction. Panic follows, and the natural reaction is to stamp ever harder on the brake, which makes things worse.

Advanced driving manuals recommend cadence braking, in which the brake pedal is pumped up and down in quick succession to ensure that the wheels never lock. But, in practice, few drivers have the skill or experience to do this in an emergency.

Anti-lock brakes are designed to auto-mate the technique of cadence braking, taking the skill out of the hands and feet of the driver and entrusting it to a package of electronics and hydraulics. They consist of two parts: an electronic sensor that can detect how rapidly the wheels are decelerating, and a system for automatically controlling the hydraulic pressure on the brakes to achieve the best and safest deceleration.

The sensor consists of a slotted or toothed exciter disc attached to an axle or inside a brake drum. As the axle turns, each tooth and gap in this disc pass close to a monitor and generate a current, which varies according to the rate at which the disc is rotating.

The signals are interpreted by electronic circuits, which determine both the speed of the disc and the rate at which it is decelerating. If the disc is slowing down too rapidly and is about to lock, the circuits instruct the hydraulic controls to reduce brake pressure, preventing a skid. As the driver continues to press the brakes, pressure rises again, and the system repeats the operation until the vehicle has stopped. The system can produce up to 45 cadences a second, if required.

The details of how the electronic signals are used to control brake pressure depend on individual designs. Some of earliest non-skid brakes, in the 1960s, were fitted to trucks, which use air under pressure to activate their brakes. In these systems it is relatively simple to bleed off some of the air through a valve to reduce pressure. The air lost can easily be replaced by drawing on air stored under pressure in the vehicle.

The same simple arrangement cannot be applied to cars, which use hydraulic fluid. This is because there is little fluid in reserve, and also it would be both expensive and dangerous to spill bled-off hydraulic fluid all over the road. One alternative is to reduce pressure by briefly increasing the volume of the hydraulic system — with a piston arrangement, for example — and then to restore pressure again. Among the systems that have been developed are some that even allow sharp turns to take place safely during heavy braking.

Although anti-locking brakes were originally available only on the most expensive cars, they are increasingly becoming standard, or optional, on most new cars.

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The Czech playwright Karel Capek introduced the name robot in the early 1920s. He wrote a play called Rossum’s Universal Robots in which an army of industrial robots became so clever that they took over the world. Capek coined the word robot from the Czech robota, which means ‘slavery’. Since then men have worried not so much about robots taking over the world, but more about robots taking over their jobs.

Robots have indeed taken over some jobs — dull, mechanical, routine work. They save costs because there is no need for them to change shifts, they do not tire or lose concentration, they do not take tea or coffee breaks, they do not fall ill (although they may need repairs), and they do not go on strike. But even though American and British researchers have produced robotic four-fingered hands capable of picking a flower, robots are still a long way from having the perception, dexterity or flexibility of human beings.

 It is, however, generally accepted that the responsible use of robots in industry is beneficial because it saves people from doing dull and dangerous jobs. Robots were used to clear up the radioactive debris after the Three Mile Island nuclear accident in America in 1979. They are also being developed for inspecting and manufacturing nuclear plants, fighting fires, Felling forest trees, and acting as security guards — walking burglar alarms that can warn human guards of an intruder. And I four-legged, 72 ton robot was used to roll boulders to build up the sea wall in Tokyo Bay, Japan, in 1986 — saving 50 divers from the risky task.

Experiments are also under way with robots that can help infirm and disabled people to be independent. Researchers in Britain and America are developing robots that can respond to spoken commands. They will be able to undertake such tasks as brushing teeth, serving soup, loading a computer, opening filing cabinets and picking up mail.

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American motorists were able to buy petrol with oil company credit cards before the First World War, but the age of the credit card dawned in 1950 with the introduction of the Diners Club charge card by American businessman Frank McNamara. The idea came to him after dining in a New York restaurant and discovering he had mislaid his wallet. The Diners Club card is not strictly a credit card because the whole bill has to be paid when the invoice is received — most other cards carry forward a debit balance.

Today there are more than 350 million credit or charge cards in use in the United States alone. Worldwide, cards are numbered in billions.

Smart cards are likely to have a wider use than for money transactions. in the late 1980s some medical authorities in parts of Europe, the USA and Japan began trials with medical identity cards —smart cards carrying the holder’s medical history. The cards save time and paperwork, as they can be consulted by doctors and chemists in computer terminals at hospitals, surgeries and pharmacies, and updated each time the patient is seen. The European trial programmes aim to produce a standardized EEC care or health smart card for use in the 1990s.

Also available are laser cards, developed in the USA, in California. They are not as smart as smart cards, but are able to carry a much larger store of personal information, contained in a pattern of tiny holes — only a thousandth of a millimetre across — on a photosensitive strip. The dots, like the pits and flats on a compact disc, can he read by a laser scanner in a special terminal.

The card can hold coded identification details, including fingerprints, signature, voice print, and even a photograph,’ as well as various hidden security codes making it -virtually impossible to counterfeit Its information storage space is so vast there is plenty room for such things as bank accounts, medical history and educational attainments. Information is filed on the card under separate access codes, so the bank, for example, could read out only financial information and the doctor only medical information.

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Every successful shopkeeper needs to know which goods are selling well and which are going slowly, so that he can restock or phase them out, as appropriate. For the small shop, tidy bookkeeping and a glance at the shelves may give all the information necessary. But supermarkets and other big stores need quick and accurate records of a much larger flow of merchandise. That is why they use bar codes, which are printed on the packaging.

A bar code can be read by a laser scanner, which passes it to a computer. This supplies the details and price of the goods, records the sale for storekeeping, totals the bill, and feeds the information to the cash register which prints out a receipt.

Common bar codes are European Article Numbers (EAN), based on a number with 13 digits, and Universal Product Code (UPC), based on a number with 12 digits. The Australian Product Number (APN) is also based on 13 digits. Each digit is represented by a series of parallel straight lines and white spaces. The laser scanner translates the information into binary digit signals, which it feeds to the computer.

The code gives the manufacturer details of the product and the package size, and includes a security code that prevents anyone altering it or the scanner misreading it. The computer supplies the price from the product information. So the only way to change the price of an item is by altering it in the computer.

 A laser scans a bar code with a beam of light passed from one end to the other. It is sensitive enough to read from left to right or right to left. Although the bar codes are usually printed in black on a white background, a laser can read a bar code which is printed in any dark colour except red, and the background can be any pale or pastel colour. Some of the lasers used scan with red light, so cannot pick up a reflection from red.

Bar coding is faster and more accurate than other systems. Human error is limited because staff do not have to mark a price on every item, and checkout assistants do not have to key in prices at the register. However, because the computer sup-plies the prices at the checkout, the store management has to ensure that the goods on the shelves display the same prices. Also that the shelf price is changed if a computer price is altered, or a customer may appear to he charged the wrong price.

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Chips are produced several hundred at a time on a slice of ultra pure, artificially formed silicon crystal, so thin that it would take about 250 slices to form a piece 1in (25mm)thick. Layout diagrams for circuits are prepared on a computer, then each reduced to chip size and set out side by side on a glass plate known as a mask. Because witches and other components are built up in separate layers on the chip, a mask is made for each operation. The masks – which block out the unwanted parts – are made many times larger than the chip and reduced photographically.

The chips are built up by forming each layer – p-type or n-type layers or insulating layers of silicon dioxide – and etching out the unwanted parts. This is done by treating the layer with a coating sensitive to ultraviolet light, masking it, then exposing it to ultraviolet light. The exposed parts become resistant to acid, but the blocked-out parts do not – they are etched away when the layer is coated with acid.

Parts such as aluminium contacts are deposited in the areas etched for them as a vapour. When hardened, the aluminium is etched to add the required circuit connections, which lead to contact pads at the edges of the chip.

All completed chips on slice are tested with delicate electrical probes to check that they are working properly. About 70 per cent prove faulty. They are marked as rejects and thrown away. After testing, the slice is cut into individual chips under a microscope with a diamond-tipped cutter. The good chips are each mounted in a frame that is encased in plastic. The contact pads are linked to metal connectors are in turn linked to protruding legs, or pins, that plug into the external circuit.

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Transistors are the commonest components in a microchip. They are used mostly as switches, letting current through to represent the binary digit 1, or cutting it off to represent 0.

A widely used type of transistor has two islands of n-type semiconductor in a larger base of p-type. While the transistor is switched off. The free electrons from the layers drain into the p layer and are absorbed by the free holes. The transistor is switched on by applying a voltage from a separate low-power circuit to an aluminium gate above the p base. This voltage attracts the free electrons from the p base towards the gate. They then form a bridge between the two n islands and provide a path for the current through the circuit in which the switch is operating.

The transistor is switched off by cutting off the power. The free electrons then drain back to the p base and are absorbed by the free holes. Without the bridge they formed between the islands, current cannot flow through the circuit.

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Pure silicon is an insulator — it does not conduct electric current However, if it is impure — containing certain other elements — it will conduct a weak current. So it is called a semiconductor, halfway between an insulator and conductor. Semiconductors allow the delicate control of current needed for demonic devices, such as transistors, to an extent impossible with full conductors such as metals. A semiconductor is made by adding elements – usually phosphorus or boron — to the silicon. if a small amount of the phosphorus is introduced as a gas while the silicon crystal is being formed into a chip, the phosphorus atoms bond together with some of the silicon atoms. Four electrons in the outer layers of each type of atom pair off, but one phosphorus electron is spare, so it is left free to form an electric current when a voltage is applied. Electrons are negatively charged, so this type of crystal is called an n- type (negative) semiconductor.

If small amount of boron is mixed with the silicon, there is one electron short in the bonding system, leaving a hole that attracts five electrons. Free holes create a positive charge so the crystal is called a p-type (positive) semiconductor. These two types of semiconductor are formed in sections within one crystal for most microchip components.

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Within an area no bigger than a shirt button, a microchip holds as many as 450,000 electronic components. They are linked into electric circuits and are visible only under a microscope.

Microchips have transformed modern life and made some of the science fiction of the past into reality. They regulate digital watches, set programs on washing machines, and beat us at video games. They also manipulate robots on car-production lines and control national defence systems.

Electronically, the circuits that make up a microchip are not particularly complex —many are just switches. Their wizardry lies in their minute size, which allows signals to flow through at lightning speed. So they can carry out up to 250 million calculations in a second.

Most microchips are made of silicon, one of the most abundant elements on earth, and easily obtained from sand and rocks. A few are made from gallium arsenide — a compound of arsenic and the metal gallium, found in minerals such as coal.

 Chips for everything

There are various kinds of microchip. A microprocessor chip can be a computer in itself – in a washing machine, for example. Or it can be the nerve centre of a larger computer, controlling all its activities.

Memory chips store information in computers on sets of identical circuits —either permanently or temporarily. Interface chips translate the signals coming into the microprocessor from outside — such as from a keyboard — into binary code so that the electronic circuits can handle it. They also translate the outgoing signals back into figures or words for the computer screen.

Clock chips provide the timing needed for all the computer circuits to process electric signals in the right sequence. Each is linked to a quartz crystal that vibrates at a precise frequency.

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In 1944, a child’s disappointment having to wait several days to see the photograph her father had taken led him to devise a quick method of film processing.

He was an American, Dr Edwin Land of Cambridge, Massachusetts, and in just a few months he had come up with a solution. Within three years the first instant-picture camera came on the market, capable of producing a finished black-and-white picture in about a minute. He called it the Polaroid-Land camera.

Today, a Polaroid camera can produce a black and white print in as little as ten seconds and a colour print in only a minute. The secret behind instant photography lies in the film, not in the camera. The film not only has a coating of light sensitive emulsion like a normal photographic film, but also carries the chemicals necessary to process it.

The film pack has both negative and positive sections – in a colour film each is many-layered, with dye developer layers alongside was colour-sensitive negative layer. The processing chemicals that trigger off the developing and printing process are in jelly-like form in a tiny plastic pod between the negative and positive sections.

The pod bursts when the film is removed from the camera through a pair of rollers. The chemicals are spread evenly over the film, and diffuse through it to set the picture processing in motion. The sandwich of film and print material develops in daylight outside the camera, and a positive picture is revealed when the negative and positive layers are pulled apart.

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Two of the mist widely used cameras are the compact and the single-lens reflex (SLR). Both use 35mm film, although a few SLRs, including the Hassrlblad, use 120 film – 2¼ in (60 mm) wide – which needs less enlarging so gives better definition.

The two types differ in two main ways. First, most compacts have one built-in lens whereas the SLR can be fitted with a variety of interchangeable lenses. Secondly. The compact has a separate viewfinder whereas the SLR has a reflex viewfinder which ‘sees’ through the camera lens.

With a separate viewfinder, the photographer’s view does not coincide exactly with that of the lens (this is known as parallax error), so some compensation is needed for close-ups. With a reflex viewfinder, the photographer can see exactly the image that will be thrown onto the film, because light entering the camera lens is reflected by a mirror through a pentaprism (a five-sided prism)
 to the viewfinder eyepiece. The pentaprism reverses the mirror image and presents it to the eye the right way round. When the shutter release is pressed, the mirror springs upwards to let the light from the image onto the film.

The compact is smaller than the SLR, is easy to operate, and has few controls. The most expensive models have automatic focusing, automatic exposure, a zoom lens, built-in flash, and motor-driven film wind-on. They can take pictures comparable in quality to many SLRs.

SLR cameras can be programmed for auto-exposure in different ways – for example, a suitable aperture is automatically chosen for a manually selected shutter speed, or the other way round. Often the exposure meter has an indicator in the viewfinder to show the combination of aperture and shutter speed being set for optimum exposure.

The latest S;R models have built-in microprocessors controlling auto-focusing, auto-exposure and motor-driven wind-on. They can be fitted with a range of interchangeable backs offering different features, such as using different film and printing various information on the film.

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Developing the first stage in film processing amplifiers the chemical changes begun by the light. It is done in the dark as the film is still light-sensitive.

In the darkroom, the film is immersed in developer, a fluid chemical mixture that reveals the image as a negative, so called because it is darkest where most light has reached the film. This is because the developer reduces the exposed silver halide grains to fine particles of metallic silver, which appear black. Before the developed film can be handled in the light, it has to be fixed – that is, unexposed silver salts are removed by immersing it in a chemical such as ‘hypo’ (sodium thiosulphate).

To make the negative into a positive print of the original scene, it is put in an enlarger and focused on silver halide coated light-sensitive printing paper. The enlarger projects the negative image on the paper at the size required, the exposes it to light. The paper retains the image in the same way as the film, but the darkest parts of the negative let through the least light, so the original light pattern is re-created. After exposure, the print is developed and fixed in a similar way to the negative.

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The film that captures the light rays is a strip of transparent plastic (polyester or triacetate) covered with a light sensitive coating. The coating is a compound of silver salts and a halogen element forming tiny silver halide grains, suspended in gelatine. Exposure to light makes the silver halides start to break down, to eventually form an image in silver.

For the best result, there must be exactly the right amount of light. Too little will result in underexposure, lacking detail because the print or slide is too dark. Too much will produce an overexposed result, lacking detail because it is too light.

Films with large light sensitive grains are quicker to react and are termed fast films. Slow films have small grains and need extra light for exposure. Films are graded for speed on the ISO (International Standards Organisation) scale. The higher the ISO number, the faster the film.

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With a modern camera, you need do no more than press a button to take a photograph – to snap the action of a sporting event or record the beauty of a prizewinning rose, for example –and make a permanent record of a fleeting moment.

Technology has taken the guesswork out of the picture taking, there are now computerized automatic cameras that focus themselves, set their own controls, and wind-on the film after each shot. In contrast there are also simple throwaway cameras that are disposed of once the film has been processed.

All cameras, no matter how sophisticated or how simple, work in much the same way. When you click your camera to take a picture, you are opening the shutter for a brief moment to let light through the lens to a dark interior. In this moment, the light rays from an inverted image of the scene in front of you on the light-sensitive film at the back of the camera.

Processing the film completes the chemical changes begun by the light striking the film, and printing the film provides a pictures of the scene you snapped.

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Sunlight is broadly made up of the three primary colours of light: blue, green and red. All colours can be made by different mixtures of the three. Pairs of primary colours produce secondary colours: magenta (blue and red), yellow (green and red), and cyan (green and blue). If secondary colours are paired, they produce the primary colours. Magenta and yellow make red, cyan and yellow make green, cyan and magenta make blue. Each of the six colours takes no part in making up the colours opposite to it in the charts. Blue and yellow are ‘opposites’, so are green and magenta, and red and cyan.

Negative and print

A colour film has three layers, each sensitive to one of the primary colours. When a photograph is taken, each layer records a primary colour but forms an image in dye of the opposite colour to the primary.

The negative is then printed by light in a darkroom on paper that contains similar colour-sensitive layers. When normal light passes through the blue wheel on the negative, the yellow dye blocks the blue rays but lets through the red and the green. The paper records the red and green cyan and magenta dyes (their ‘opposites’). When you look at the photograph the combination of cyan and magenta appears blue. All the other colours are produced in the same way.

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When you take a photograph the subject that you see through the viewfinder is recorded on the film during the brief moment that the shutter opens to let in light through the lens. The film is coated with an emulsion that is chemically affected by light. ‘Fast’ films are more sensitive to the light than ‘slow’ films, so can be used in duller conditions. The speed of the film is indicated on the box and the spool by the ISO number. The higher the number, the faster the speed.

The camera lens concentrates light from the subject of the photograph and projects an inverted image of it onto the film at the back of the camera.

The diaphragm has overlapping leaves that form an aperture which can be made larger or smaller. A big aperture lets more light enter the camera.

A common type of shutter has two blades that open to form a slit that crosses the film. The smaller the slit, the faster the shutter speed.

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Busy executives and technicians can carry their own personal buzzer – rather like a pocket electric bell – to warn them which they are wanted. Doctors on their rounds in a sprawling hospital, for example, can be called to a particular ward, or firemen on routine duty to a fire alert.

The pocket alarm, known as bleeper (or beeper) because of the sound it emits, to a battery-powered miniature radio receiver turned to one station. The bleep is made by a tiny crystal that vibrates to produce sound when electric signals are passed to it. The signals are generated in the bleeper’s electronic circuits, triggered by a radio signals transmitted at the touch of a button from the control unit.

The simplest bleeper can emit several different signals, rather like the dots and dashes of Morse code. Four long bleeps, for example, could mean ‘Ring the office’, or interspersed long and short ones ‘Come to reception’. More advanced types can display short message, or can store messages.

The system is known as radio-paging. A small network can call up to about 100 receivers, either separately or simultaneously in a group. Each receiver has a number, and the controller makes contact by sending the receiver number and then the required message.

Long-range paging services are operated by commercial companies who transmit messages to their subscribers’ bleepers from a control room. The world’s largest paging network is operated by British Telecom, who have transmitters covering various zones throughout the country.

Radio-paging systems all have to be licensed, and are allocated a frequency, generally around the 27mHz waveband in Australia. The operating range varies according to the power of the transmitter but could be 100 miles (160km).

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Newspaper have been using facsimile machines to send photographs (wire photographs) since 1907, when a photo from Paris was wired to the Daily Mirror in London. In 1959, a Japanese newspaper Asahi Shimbun
(‘Morning Sun’), sent whole pages from its main office in Tokyo to a printing works at Sapporo 600 miles (960 km) away. Now it sends a complete copy daily by satellite link to London, where it is printed, for sale in Europe.

In recent years, technological advances have resulted in cheaper machines able to give good quality reproduction. Newspapers and business firms are not the only users. Police forces can send each other copies of fingerprints and photo fit pictures.

The earliest fax machines took about six minutes to transmit a document the size of an A4 typing sheet. Later machines cut the time by half. Modern machines take less than 30 seconds. They code the information digitally although it is transmitted as analogue (like sound-wave) signals. Machines available in the 1990s will both code and transmit digitally, cutting A4 sheet transmission time to four or five seconds.

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Telephone cables carrying messages at the speed of light have given a new lease of life to telecommunications. The amount of information now transmitted – telex, fax and computer data as well as telephone calls – was straining the copper-cable system to the limit. Fibre optic cables, with thir high capacity, small size and freedom from electrical interference, are the key to development.

The first uses of optical fibres was in medicine in 1955, for lightning up parts of the inside of the body. The light loss through the fibres was at first too great for many other uses. But in 1966, Dr Charles Kao and Dr George Hockham, two scientists working in Britain at the Standard Telecommunications Laboratories, discovered that the loss was due to impurities in the glass. By 1970, due to impurities in the glass, Corning Glass, had produced fibre optics good enough to transmit telephone signals.

Fibre-optic cables are now gradually replacing copper ones between exchanges. The first transatlantic fibre optic cable, TAT-8 – jointly laid by American, French and British companies – began service in 1988, its capacity of around 40,000 simultaneous telephone calls is three times as great as the seven existing copper transatlantic cables put together.

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All electromagnetic waves travel at the speed of light – about 186000 miles (300,000km) per second. They are called electromagnetic because they consist of both electric and magnetic fields acting at right angles to each other. The fields leapfrog each other, giving the wave its motion like the snaking of a length of rope when it is jerked.

The height of a loop half the distance between the customer and the trough is called the amplitude. Waves can also be measured by their frequency, that is, the number passing a given point each second. The longer the wavelength, the lower the frequency.

Frequencies are measured in units called hertz, named after the German, Heinrich Hertz, who in 1888 demonstrated that electric signals could be sent through the air.

He passed a high-voltage current through a loop of wire that had a metal sphere at each end, causing a spark to jump the short space between them. At the same time, another spark jumped between the spheres of a separate, similar wire loop placed on the other side of the room.

Hertz proved that the energy transmitted from one loop to another was electromagnetic radiation, which had been predicted theoretically by a British scientist, James clerk Maxwell, in 1864.

The hertz measurement of a frequency gives a number of complete waves, or cycles, per second. Frequencies are usually expressed as kilo hertz (thousands of hertz), megahertz (millions of hertz) or gigahertz (thousand millions of hertz). Light waves are extremely short. The longest, the red, measure about 36,000 to an inch (14,000 to a centimetre) and have a frequency of around 100,000,000 MHz. Radio waves used for communication, however, range in length from about 1/25 of an inch of (1 mm) to about 18 to 20 miles (30 km), and have frequencies ranging from 10,000 Hz to about 30,000 MHz.

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Although television is thought of as a 20th century invention, its beginnings date back to the 1880s. The first ideas about transmitting pictures over a distance were considered in the years following the introduction of the telephone. If voices could be sent over a long distance, why not pictures?

From the beginning, it was realised that pictures could not be sent as an entity, and ways of breaking down and then reconstructing a picture were suggested by a German inventor, Paul Nipkow, in 1884. Nipkow used spinning perforated discs to dissect and then resurrect a black-and-white image.

In 1906, Russian scientist, Boris Rosing, put together the scanning principle of the  Nipkow disc and the display possibilities of the cathode ray tube invented by a German, Ferdinand Braun, in 1897 to create the first crude television system. The cathode ray tube is still the vital component of modern television.

Experimental broadcasts were begun in America in in 1928, but the first practical television system was set up by the eccentric Scottish inventor John Logie Baird in London. He opened the first television studio in 1929, and used Nipkow discs for scanning in both transmitter and receiver. Within a few years, however, Baird’s mechanical disc – scanning system was overtaken by the electronic camera invented by the Russian Vladimir Zworykin, who produced the first practical one in 1931.

The first three day a week television service began in Berlin in 1935, operated by Fernseh, a German company with which Baird was involved. Britain BBC opened the first public high-definition service in 1936, and RCA began transmission in America in 1939. Colour transmission started experimentally in the USA in 1951.

Cable television began in the United States in the 1950s, with commercial company sending programmes to subscribers along cables. This allows more channels than radio transmission. In Britain in Europe, cable television did not arrive until the 1980s.

Sometimes cable television is also partly satellite television, programmes being relayed by satellite to company dish Aerials at a central station, then sent out to homes through the cables.

Other television systems introduced or under review in the late 1980s included microwave television carrying up to 60 channels over short distance, high definition television (HDTV) using over 1200 screen lines and direct broadcasting by satellite (DBS) to small domestic dish aerials. For this the transmitting company has to code the signal so that only a subscriber with the decoder on the set can receive them.

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The coming of the computer and the exploration of space sparked the need for increasingly complex yet small, durable, and often remotely operated controls. This has brought about the age of microelectronics, which began in the 1950s centred around the transistor and silicon chip. It is a silicon chip that is the heart of the remote control that you see use to switch on your television set from the armchair.

When you press the button on the remote control, the chip which contains a microelectronics circuit sets off an electronic oscillator (vibrator). This produces an infrared beam, which is made up of electromagnetic waves.

The beam carries a coded signal, the code varying according to the button pressed to switch on, change channels, or raise volume, for example. The code based on binary digits is superimposed on the beam in the same way that a radio signal is superimposed on a carrier wave.

In the television set, the coded beam is received by a device sensitive to infrared waves. The incoming signals are amplified and fed to another silicon chip that identifies the code. The chip then feeds the appropriate signal to electronic switches that carries out your instruction.

Ultrasonic remote controls can be used to open or close the garage door. They emit high-frequency sound waves that are directed to receiving microphone. This send signals to an electric motor that operates the doors. However, the ultrasonic control must be operated in the direct line to the doors, so radio control is no more often used. A hand-held radio control is a miniature transmitter that can open garage doors fitted with a receiver from anywhere in the vicinity. The radio waves switch on an electric current to the motor that operates the doors.

A more complex radio control system is used to operate model aeroplanes and boats. The hand held transmitter sends out beams of coded radio waves. A miniature receiver on the model decodes the signals, separating them from the radio waves. The decoded signals are fed to tiny electric motors, called servos (short for servo-mechanisms, which increase their power). The servos open and close the engine throttle, raise and lower the landing gear, and operate the control surfaces such as ailerons and rudder – on the wings and tail.

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A home Video recorder picks up electrical signals from the television station at the same time as your television set. But instead of converting the signals directly to pictures, the video stores them on magnetic tape in the same way that a tape recorder stores sound signals. Because television signals carry pictures as well as sound, home video tape is generally four times the width of a sound cassette tape.

Is the video recorder is connected directly to the aerial, it picks up television broadcasts when switched on, whether or not to the television is on. Both can be turned to pick up different programmes at the same time.

The two main videocassette a recording system is available are Betamax, introduced by the Japanese company Sony and in 1975, and VHS (video home system) pioneered by JVC (Japan Victor company) in 1976. Each system needs different cassettes different recorders. Betamax produces slightly better quality pictures, but VHS tapes can run longer up to 4 hours. VHS has proved the more popular of the two and new Super VHS has better quality pictures than either of the standard systems.

Recording and playback

When a video tape cassette is fitted into the video recorder and the record button pressed, the machine draws a loop of tape from between the two reels in the Cassette and wraps it round a rotating drum driven by an electric motor.

The picture recording heads, usually two, or mounted on the drum facing outwards, and imprint the signals on the tape as they rotate with the drum. The heads are tiny electromagnets, and operate in the same way as for sound a tape recording.

The tape runs past the drum at an angle. The picture signals are recorded in the central area as a series of sloping tracks, and the accompanying sound signals are recorded as lengthways tracks along one edge of the tape.

As with the tape recorder, playback is a reversal of the recording process. When the tape is loaded and the play button pressed, the stored signals on the magnetic tape produced electrical signals in the playback head. This feeds the picture and sound signals to the television set, where the recording is recreated on the screen.

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A German physicist named Heinrich Hertz first demonstrated in 1888 that it was possible to transmit electrical energy through the air.

Between 1894 act 1896, the Italian scientist Guglielmo Marconi developed a method of using Hertzian waves to send signals in Morse code – a method that became known as wireless telegraphy. By 1901 Marconi had improve the system so much that he was able to send wireless telegraph signals across the Atlantic from Cornwall to St John’s Newfoundland.

A Canadian engineer made the world‘s first public radio broadcast from Massachusetts, USA, heard by ships around hundred miles (160 km) away on Christmas eve, 1906. He was Reginald Aubrey Fessenden, who had a found a way of combining the signals from a microphone with an electromagnetic waves. The name radio was given to the method.

At first, listeners had earphones linked to receivers that used crystals to pick up the radio waves. These eventually give way to sets with loudspeakers, diode value (invented by an English man, John Ambrose Fleming, in 1904), and more powerful electronic circuits following the American Lee de Forest’s invention of the triode valve in 1907. With the earliest valves (used to amplify signals), sets had to be switched on to warm up for five minutes before the programme begins.

Regular public broadcasting did not begin until 1920, from the radio stations in Pittsburgh and Detroit. Edwin H. Armstrong, an American engineer, improved the receiver in 1924, and by the late 1950s, compact transistors were replacing bulky valves.

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Until the 1970s, most the telephone calls were transmitted as electric signals corresponding to the vibrations of the voice. These are known as analogue signals because they are analogues – similar in structure – to the sound. Electrical interference in the transmitting circuits can distort voices.

After the 1970s, the analogue system began to be replaced by a digital system which cuts out most interference and distortion. The analogue electrical signals from the microphone are changed to binary numbers in electronic circuits at the exchange and transmitted in coded form.

To do this, the wave heights of the electric current are measured thousands of times every second. The measurement is expressed as a sequence of the digits one and zero. Current is then converted to a series of pulses – a flow for 1 and a break in-flow 0 – representing the wave measurements. This is known as pulse-code modulation (PCM). As each pulse is very short, the pulses of one telephone message can be interleaved between the pulses of others.

This technique of time multiplexing allows 32 simultaneous calls to be sent along a single pair of wires, or thousands of messages to be sent at once along the same coaxial cable.

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Two wires, or conductors are needed to complete the circuit between the telephone transmitter and receiver. Some exchange cables carry thousands of pairs of wires.

 If every call needed a separate pair of conductors for transmission throughout the telephone network, the simultaneous transmission of thousands of calls from one exchange to another would be unmanageable. A pair of ordinary copper wires can be made to handle only a limited number of calls at once because they are designed for low-frequency current. Higher frequencies would allow more simultaneous calls, but unless a different design of cable is used, the signal radiates away and loses strength.

Most trunk lines between telephone exchanges are now coaxial cables, in which the signal is confined to prevent loss of strength and interference. Instead of a pair of wires, each coaxial cable has a central copper wire with an outer copper conductor that sounds it like a sleeve. They can handle high frequencies and carry thousands of calls. Built in amplifiers boost the signals about every 1¼ miles (2 km).

Using a technique known as frequency multiplexing, the electric signals corresponding to the voice sound waves are modulated – that is, combined with an electromagnetic carrier wave in the same way as radio waves. A number of carrier waves of different frequencies are then sent along the same pair of conductors.

At the receiving exchange, the signals are separated from the carrier wave by a process called demodulation. The other then filtered to the correct receiver.

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When you lift the receiver and complete the circuit to the exchange, dialling the number sends a series of electrical pulses down the line. Older telephone exchanges have automatic electromechanical switch gear, named after the American, Almon Strowger, conceived it in 1888. This has banks of fixed contacts, each in a half circle round of mobile selector arm.

The number is selected step by step. The first dialled digit sends the arm up to a bank corresponding to the digit. The arm then rotates to find a free contact – one that will connect it to the next bank ready for the next digit dialled. If no contact is free, the engaged tone is sounded. If contact is made, the next selector arm searches for that second digit, and so on. The final selector makes contact with the line of the number being called.

If the selector accidentally touches and sticks on an incorrect contact for the digit dialled, you get crossed line.

The latest telephone exchanges work electronically. Dialling sets up audible tones, and connections are made by circuits incorporating microchips that interpret the tones. Because there are no moving parts, electronic switching is silent and more reliable than electromechanical gear and crossed lines are rare.

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Over 500 million telephones are now in used throughout the world. In just over hundred years since the Scottish born inventor Alexander Graham Bell patented the first telephone in 1876 – telephones have revolutionized world communications.

Today, telephone networks relay not only voices but pictures and written information as well, by land and sea cables and through the air on microwaves, which are super-high-frequency radio waves. Calls can be made across half the world with less than a second delay in connection, and no difficulty in hearing. Multinational companies can even hold cross world video conferences, with executives speaking to each other from one screen to another.

Satellites, microchips and lasers

The modern inventions that have made this revolution possible include space satellites, microchips and laser beams. Early bird, the world’s first commercial satellite, was launched in 1965 by the International Telecommunication Satellite Organisation (INTELSAT).

Now there are about 130 satellites orbiting in space, relaying messages on microwaves from Earth Station to Earth Station. The orbit the earth at heights of about 22,500 miles (36,000 km) above the equator once every 24 hours, so appear to remain in the same place.

From the earth stations, microwaves carrying messages are beamed up to the satellites from huge dish aerials, some of which are 98ft (30 m) across. They are computer controlled so that they will always point directly at the satellite. Microwaves are not only used for satellite links – dish Aerials beam messages across land too, in straight lines from tower is located to ensure a clear path.

Microchips on the satellites amplify the relayed signals. Microchips have also brought about clearer, speedier communication by providing the fastest switching needed for sending telephone messages by digital transmission. And lasers have enabled the use of fibre optic cables – glass thread that carry digital messages at the speed of light, so fast that they could go seven times round the earth in a second.

Telecommunications services now available include fax, radiopaging, cordless telephones, car telephones and even aircraft telephones, allowing passengers to make calls while flying.

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When your clock radio starts playing music first thing in the morning, or the oven automatically comes on to cook a meal, the switch has probably been operated by a digital clock.

At the heart of the switch is a quartz crystal which vibrates at a fixed frequency when connected to a source of electrical power – battery or mains. The vibrations produce regular electrical pulses, which travels through circuits in a microchip to operate the digits on the clock.

The switch also has a memory, in the form of a microprocessor, which stores the time when the radio, oven or central heating system has to be turned on. The microprocessor constantly compares the stored time with the real time as measured by the clock.

When the turning on time comes, it sets off a low-voltage electronic signal. This signal is amplified by a transistor circuit and flows through a relay, an electronic device in which a small current causes a metal contact to move, switching on the main current.

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Car tyres are not just cushions for the wheels. They are there to give the car a good grip on slippery roads, and stop it sliding about when braking or cornering.

The tread pattern running all round the tyre has thin cuts (known as sipes) in the rubber to sponge up surface water, and zigzag channels to pump the water out behind as the car rolls forward. On a wet road, a tyre has to move more than 1 gallon (5 litres) of water a second to give an adequate grip.

On a perfectly dry road, the treads are not needed. A smooth tyre gives the greatest possible area of contact with the road. But if the smooth tyres are used in wet weather, the film of water on the road builds up in front of them and underneath them and actually lifts them and off the road surface – this is known as aquaplaning. When aquaplaning occurs, the driver loses control.

Most cars have to function in all weathers, so must have tyre treads, but racing cars make comparatively few outings a year. If the track is dry, they run on smooth tyres, called slicks, to get the best grip on the roads. The extra wide tyres and wheels give more grip that the average cars. In wet weather, however, the slicks have to be changed for treaded tyres.

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When you are travelling in a car, you and the car are moving at the same speed. If the car stops abruptly, your body keeps moving forward. This is an illustration of inertia – the tendency of a moving object to keep moving, or of a stationary object to remain at rest.

An inertia-reel seat belt works on the same principle. Its mechanism includes a pendulum, which hangs vertically under ordinary driving conditions. But if the car stops abruptly it swings forward, and a locking lever resting on the pendulum is released. The lever engages a toothed ratchet that locks the shaft round which the belt is wound. The locked seat belt then prevents your body from being flung forward.

When you fasten a seat belt, it winds out from the reel against slight tension from a spring. This keeps it taut during normal travelling, but allows enough free movement for a driver to reach forward as necessary. But if you tug abruptly on the belt while winding it out, the locking mechanism will engage and stop the action of the spring. Slackening the belt releases the spring and the locking lever.

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The exquisite workmanship of the traditional mechanical wristwatch has given way to the magic of the microchip. In the quartz watch, a vibrating crystal has taken over the role of timekeeper from the traditional finely tuned balance wheel ad hairspring. Minute electronic circuits control its operations.

A quartz crystal vibrates at an unvarying rate when an electric current is passed through it. The man-made quartz crystals used in watches are usually designed to vibrate 32,768 times a second when stimulated by the current from a battery. These vibrations produce electric pulses, and as the pulses travel through the electronic circuits of the microchip, their rate is successively halved in a series of 15 steps. The result is one pulse per second. Each one-second pulse triggers the chip to send signals to the digital display to advance the numerals one second.

The chip also uses the pulse as a base for other counting circuits, such as those that display hour and date, and to control the alarm signal.

Many modern quartz watches display the time in digits on a liquid crystal display (LCD). The liquid crystals are sandwiched between a reflective bottom layer and a top layer of polarised glass, and transparent electrical conductors separate them into segments. Each digit is formed from segments – up to seven are normally used, all seven being used for figure 8.

The liquid crystals rearrange their molecules according to their electrical state. Where the conductors carry no charge, light through the sandwich is reflected out again, so the display is blank. When the conductors are charged by an electric pulse, the molecules in the affected segments realign and twist the light away from the reflective surface, so the segments appear dark.

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In the split second between the pressing of the shuttle release and the opening of the shutter, an automatic camera measures the distance between the lens and the subject and positions the lens to give sharp focus.

Most compact cameras have a tiny electric motor driving a transmitter that emits a beam of infrared light. The transmitter is linked to the lens, which moves in or out as the beam scans – focusing from near to far. The beam reflects back from objects to the camera, and a sensor monitors its signals and stops the transmitter when the strongest signal shows that the lens is in focus. This automatically triggers the shutter.

Some instant cameras have ultrasonic focusing similar to the echolocation scanning system bats use to navigate. A gold-plated disc (the transducer) sends out ‘chirps’ too high to be heard by human ears, each lasting 1/100th of a second. The disc receives the chirp echoes from the subject, and a built-in microcomputer measures the time each chirp takes to go out and come back. From this it calculates the distance to the subject.

SLR (single-lens reflex) cameras with an auto-focus use what is known as an electronic phase detection system. In this, light entering through the lens is separated into two images. A sensor measures the distance between the two images, which are a specific distance apart when the lens is in focus. If the distance is not correct, the sensor causes a motor to move the lens.

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