My Science School

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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A loudspeaker works like a reversed microphone. Electric current flows into a coil of wire, turning it into an electromagnet. This attracts the coil to another magnet inside the loudspeaker, causing the coil to vibrate. This vibrates a diaphragm at the same frequency as the original sound, pushing air in front of it to carry the sound to the ears of the listeners. Many loudspeakers can be connected together, so that sound is heard all around a large outdoor or indoor space.

A loudspeakers (loud-speaker or speaker) is an electroacoustic transducer which converts an electrical audio signal into a corresponding sound.

A loudspeaker consists of paper or plastic moulded into a cone shape called ‘diaphragm.’ When an audio signal is applied to the loudspeaker’s voice coil suspended in a circular gap between the poles of a permanent magnet, the coil moves rapidly back and forth due to Faraday’s law of induction. This causes the diaphragm attached to the coil to move back and forth, pushing on the air to create sound waves.

Voice coil, usually made of copper wire, is glued to the back of the diaphragm. When a sound signal passes through the voice coil, a magnetic field is produced around the coil causing the diaphragm to vibrate. The larger the magnet and voice coil, the greater the power and efficiency of the loudspeaker.

The coil is oriented co-axially inside the gap; the outside of the gap being one pole and the centre post (called as the pole piece) being the other. The gap establishes a concentrated magnetic field between the two poles of the permanent magnet. The pole piece and backplate are often a single piece, called the pole plate.

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Inside a microphone is a metal disc, called a diaphragm. When a sound wave hits the sensitive diaphragm, it makes it vibrate at the same frequency. This causes a wire coil, beneath the diaphragm, to move up and down. As the coil comes near to a magnet below, it creates a pulse of electric current in the wire. The pattern of these pulses matches the pattern of the sound wave. The pulses can be sent along a wire to a loudspeaker, to be turned back into sound, or they can be recorded on a tape or compact disc.

When you speak, sound waves created by your voice carry energy toward the microphone. Remember that sound we can hear is energy carried by vibrations in the air. Inside the microphone, the diaphragm (much smaller than you'd find in a loudspeaker and usually made of very thin plastic) moves back and forth when the sound waves hit it. The coil, attached to the diaphragm, moves back and forth as well.

The permanent magnet produces a magnetic field that cuts through the coil. As the coil moves back and forth through the magnetic field, an electric current flows through it.

The electric current flows out from the microphone to an amplifier or sound recording device. Hey presto, you’ve converted your original sound into electricity! By using this current to drive sound recording equipment, you can effectively store the sound forever more. Or you could amplify (boost the size of) the current and then feed it into a loudspeaker, turning the electricity back into much louder sound. That's how PA (personal address) systems, electric guitar amplifiers, and rock concert amplifiers work.

Dynamic microphones are just ordinary microphones that use diaphragms, magnets, and coils. Condenser microphones work a slightly different way by using a diaphragm to move the metal plates of a capacitor (an electric-charge storing device) and generate a current that way. Most microphones are omnidirectional, which means they pick up sound equally well from any direction. If you're recording something like a TV news reporter in a noisy environment, or a rare bird tweeting in a distant hedgerow, you're better off using a unidirectional microphone that picks up sound from one specific direction. Microphones described as cardioid and hypercardioid pick up sounds in a kind of "heart-shaped" (that's what cardioid means) pattern, gathering more sound from one direction than another. As their name suggests, you can target shotgun microphones so they pick up sounds from a very specific location because they are highly directional. Wireless microphones use radio transmitters to send their signals to and from an amplifier or other audio equipment (that's why they're often called "radio mics").

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