Monday, April 30, 2012

Computer Technology

        Computer is an automatic machine which can do calculations, write and solve complex problems within seconds without making any mistake. Not only can this but it also perform many functions at a time. A signal computer can do millions of calculations within a second.

            Computers are being used successfully in telecommunications, space research, engineering, science, industries, medicine, education, banks, transport, post offices, railways, sports etc.

            The first electronic computer was ENIAC, which was invented in 1946 by Eckert and Mauchly of Pennysuylvania University. There were 18,000 electron tubes, 70,000 resistors and 10,000 capacitors in it. Each tube was of the size of small bottle. This computer was controlled by a team of trained operators. In 1950, the transistor replaced the vaccum tube. Nowadays integrated circuits or chips are used in computers which have reduced the size of the computer considerably. Computers are of two types-------the first type of computer is called analog computer which measures one quantity in terms of the other and the other one is digital in which various problems are solved by using digits.

            A computer has three main parts------input unit, central processing unit CPU, and output unit. In the input unit, magnetic tape, punch card paper or tapes are used. There is a memory in CPU which stores the information. Its controlling system gives directions and arithmetic system performs various Operations. Printers, cathode ray tube or sound indicating units are used as output devices. In fact, the input of computer is just like our eyes and ears, CPU functions like our brain and output unit functions like our hand and mouth.

Digital Computers

            In digital computers, all information is sent through programme and these bits of information guide the functioning of computer. The data of the programme are sent to the computer through an input machine. This data is processed in the CPU. The data of programme gets stored in the memory. Calculations are done in the arithmetic and logic units. Storage and calculations are controlled by control unit and the solution of the problem is given by the output unit.

Home Computers

            The heart of home computer is only one chip which is called a microprocessor. Different part of chip performs different functions of the computer. The chip of a home computer has two types of memory, one Central processing unit (CPU) and one clock.

            Read only memory of ROM carries necessary messages for the computer. This cannot be changed. Random Access Memory or RAM is a temporary memory and it is used to give instructions and message when computer operates. The instructions given to the computer are called a programme and messages kept in it are called data. Experts wiring a computer programmes use special languages which the computer can understand. There are FORTRAN, etc. but BASIC Beginner’s all purpose symbolic instruction code is most commonly used.

Computer Software

            The programme and data fed to the computer is called computer software. We can type words ad decimal figures with keyboard which go to Random Access Memory RAM or the computer. These do not go into the memory in the form of words and decimal figures because memory cannot store them in that form. Computer changes them into binary code. In this code, all the characters are changed into 1 and 0.

            Two binary digits are called bits. Most of the computer data are controlled and stored in eight bit units, which is called a byte. The RAM of a single home computer can control about 1,28,000 bytes.

Computer Hardware

            The physical parts of a computer which we can touch are called hardware. In the main processing unit of a home computer, there is a Visual Display Unit VDU resembling the TV screen, one keyboard, mouse, joystick, printer and modern.

            Magnetic disks are fitted inside one or two slots of the processing unit. Programmes and data are stored on disks. These are called floppy disks.

            Mouse is a device which helps you to make a design directly on the VDU. Joysticks are used in video games.

            The programmes given to the computer can be received in the form of a copy printed by the printer or it can be stored on floppy disk or magnetic tapes. These can be transferred to the other computer through telephone cables. This you can do by modern, which converts computer output signals into audio signals. The modem on the other end reconverts them into original form.

            Scientists have made various types of computers today but the fastest and the most powerful among them are super computers.

Video Technology

        Video recording is a modern technique in which sound and picture are simultaneously recorded on a tape or disc electronically. Television studio makes use of video to record programmes and feature films. Video films can be purchased from the market and can be taken to hoe to see on one’s own TV set.  Video tape costs less than ordinary films to make domestic movies. It is also very simple to use them. Disk is the latest development but it is different from the tape.

            In 1956, US Ampex Corporation developed the first video recorder. In 1976, Philips Company of Europe manufactured the first video recorder for domestic use. The most popular home video system is VHS (Video Home System). This was developed by JVC in Japan in 1970. In this, a 12.65 mm wide tape is used.

Camera and Recorder

            Video camera converts light and sound into electrical signals. Recorder converts these signals into magnetic pulses and records them on magnetic tape.

Video Cassette Player/Recorder

            Video cassette player again converts the magnetic pulses which are recorded on tape into the original electrical signals. These signals are again converted into original picture and sound in a TV set. Most of the domestic video cassette recorder machines can record as well as play the tapes. You can record TV programmes on these tapes and watch them afterwards.

Video Disc

            Video disc resembles long play record (Audio LPS). You cannot record your own programmes on these discs. They are pre-recorded. A special type of disc player is required to play them.

            Video disks are of two types: one is used like audio player and for the other; a thin laser beam is used. Laser disc is like a silver mirror which shows rainbow color. It is played by laser beam.

            The programmes recorded on video disc are very clear. They can be preserved for a long time. They are also cheaper in comparison to video tape. These are used in the field of education, training and industries. A few video discs can be controlled by the domestic computer also.

Television Technology

        The first public demonstration of television was given by John Baird of Britain in 1926. the television which displays the different objects and scenes on the screen is a result of the systematic and joint efforts of the scientists.

        V. Zworykin of America made a significant contribution in this field. In 1928, he developed an electronic system, which superseded Baird’s mechanical system. It was a revolutionary development for telecasting programmes quickly and correctly.

            To telecast TV programmes, sound and scenes are first converted into electromagnetic waves. These waves are again converted into sound and scene by the TV set. A TV camera consists of an orthicon tube. The image of the scene formed through a lens falls on a photosensitive plate of this tube. Electrons are emitted from the plate according to the intensity of light. After that, it is canned by a cathode ray tube. Scanning changes the image into electric current. It is called a video signal. It is telecast after amplitude modulation. In addition to this, sound is converted into electric current by a microphone and is transmitted after frequency modulation. It is called an audio signal. These electro magnetic waves of scenes and sound hit our TV antenna. These are received by the TV set where they are converted back into the original scenes and sound.

            The working of color TV is almost the same as a black and white TV. The light coming from the scene is divided into the three primary colors by three filters fitted in the camera. One filter allows only red color to pass the second only blue ad the third only green. The light of each color falls on different camera tubes. Each tube contains a separate glass plate and electron beam. The three signals from the tube reach the transmitter. The three signals from the tubes reach the transmitter. The TV transmitter mixes these three signals into one. A black and white signal is also mixed with this signal. After that, these signals are sent to the transmitting antenna and telecast. This signal reaches our TV sets. Three electron guns, one for red color, the second form blue and the third for green are fitted in the TV set. A layer of about 125 lakh phosphor dots of the three colors is painted on the screen of the TV set. These dots are arranged in a pattern of three and emit light when electron beam falls on them. Out of these dots, one emits red light, the second blue and the third green. The color emitted form each group of dots depends upon the intensity of electron beam. The colored scene is created on the screen by mixing of these three primary color in different ratios.

DBS TV

            Artificial satellites brought about a revolution in the art of TV transmission. TV stations telecast programmes for different countries with the help of satellites. Nowadays, direct transmission is also done from the satellite. This is called DBS Direct Broadcast Satellites. In this system, our TV set receives signals directly from the satellite. This system requires a special dish aerial.

Cable TV

            In cable TV, the signals reach our TV set through a cable. Nowadays, a dish aerial is installed in a colony and programmes can be viewed by the people of the colony on their TV sets through a cable. More channels can be transmitted through cable than ordinary transmission. TV signals can be sent to hills, valleys and even tall buildings with the help of the cable. Cable TV has become very popular these days.

Satellite Communications

        Telecommunication messages are not only broadcast through telephone cables but through satellite also. Everyday, thousands of phone calls, tv signals and computer data are transferred from one part of the world to another through satellites. A communication satellite can handle more information than cable and communicate them much faster.

Sending Signals

            Messages are sent to the satellite from any earth station in the form of microwave signals. Microwaves are a type of short radio waves and can travel through space with the speed of light. Signals are sent and received through dish shaped antennas. The messages sent from the earth station are received by the satellite and are retransmitted to the earth. The antennas located on earth receive the messages and send them to the destination. These messages can be for telephone, radio or television.

Using Satellite

            We can use telephone, radio and television messages to any part of the world with the help of communication satellites very easily. Any event can be telecast live from any part of the globe. Now, it is possible to transmit a telephone call which can travel around the globe and can be received at the same point from where it was transmitted with the help of communication satellites.

            Satellites have proved very useful for multinational companies. Different offices in the world can be linked to each other. Office work stations have communications between each other.

Fax Technology

        Fax or facsimile transmission is a new system of sending information on paper through telephone line. It is different from other communication system like telex and electronic mail. All types of documents, either printed or handwritten, line diagrams or photographs can be sent or received using the fax machine.

            A modern fax machine takes less than 30 seconds to send a written paper. In the beginning, fax machines were of the analog type but now digital machines are in common use.

            A fax machine scans the document by light and the image is changed into electrical signals by photocells. The message travels through the telephone line and is received by the fax machine at the other end. After decoding, the machine produces a printed copy of the original document.

            The coding and decoding system of the entire fax machine in the world is the same. So you can send the document from your fax machine to any other fax machine. Every fax machine has a number like a telephone, which has to be dialed before sending a message.

Sunday, April 29, 2012

Telephone Network

        Telephone network is the most effective and useful two way telecommunication system. With the help of a telephone, has other. The use of computers in telephones has added new dimensions to telecommunications. View data telescoping electronic banking electronic offices etc. are all born out of computers. In fact computers have added a new chapter to the phone network which has made communication systems very easy and fast.

How Phone Works:

        When we speak our sound creates vibrations in the air. The  microphone fitted in the mouth piece of the phone changes these sound waves into electric current. This current reaches the earpiece of the receiving phone through cable. In the ear piece of the phone, the electric current again changes to the original sound waves. In this way, your voice reaches the destination. This system is called analog broadcast because in this system, electric current is ‘analogous’ or identical to sound waves.

Digital Phone System:

            The binary digital system was developed in 1960. in the digital phone system, sound signals are converted in the form of 0 and 1 which represent the on and off states. Binary digit is called a bit. Seven bits are generally used in telephone communications. The receiving phone coverts these digits back into sound waves. Binary digits are fast and are of the same kind, so it is very easy to convert the4m into their original form. Nowadays, these systems are used on a large scale along with computers.

Fiber Optic Cables:

            Most of the phone calls travel through copper cables in the form of electric current, but nowadays these calls are also sent through optical fiber cables in the form of light. These cables have proved better than copper cables. Through this cable, about 10,000 telephone calls can be communicated at a time. In this system, laser beam and cable made of optical fibers are used.

Computer Exchange:

            The telephone system has not been totally digitalized in our country yet, only a few exchanges have been computerized. These exchanges control much more information in less time in comparison to the old mechanical exchanges. The chances of misconnections, crossed lines, interference or lost calls in these computerized exchanges are extremely low. Such exchanges also provide additional facilities like rerouting of a phone call for another phone, view data phone, number directories, automatic monitoring of call etc.

Cellular Radio and Telephones:

            Cellular radios or telephones are used for mobile communications. Telephones remain linked with the cables and the person using the cordless phone can use it only within a cell of a few meters form the base station. In a few parts of big cities, special types of radio channels or transmitting frequencies are used. In cellular telephone network, an area is divided into many cells. Every cell is at a distance of five kilometers form each other. When a person using a cell phone makes a call, a radio signal is sent to the nearby base station. The base station sends it to the nearest mobile telephone exchange. After that, the call is automatically transferred from the transmitter of one cell to the other cell. In this system, many calls can be made simultaneously.

Reproduction of Sound

          Sound is a kind of energy which travels in the form of waves. It can be recorded on a tape of disk by converting it into electrical signals. It can also be reproduced and heard from the tape or disk. The whole process is called sound recording ad reproduction. Sound waves are recorded on tapes in the form of magnetic patterns. On ordinary record disks, waves are recorded in the form of grooves. In a compact disk, sound is recorded as spiral patterns of microscopic pit. All these systems of recording sound are different form each other but all require a microphone for recording and a loudspeaker for reproducing the sound.

            The microphone converts the sound waves into varying electric current. A simple microphone consists of thin disk or diaphragm connected to a piezo-electric crystal. When this crystal is pressed by sound waves, a feeble electric current is generated. Sound waves cause vibrations in the diaphragm exerts a little pressure on crystal and, as a result, a feeble electric current is generated. The current produced varies as the amplitude of the vibrations and produces a sound wave pattern which is recorded on the tape or disk.
                                                               Crystal Microphone

            To listen to this sound again electric current is produced from the disk or tape and this electric current is sent to the loudspeaker.  The loudspeaker converts these electric signals into sound waves. An ordinary loudspeaker has a big cone of paper connected to a coil of wire. The cone is fitted in between the pole pieces of a permanent magnet. When electric current is passed through this coil a magnetic field is produced which causes vibrations in this cone and sound is produced. In this way the recorded sound is reproduces and heard.
Moving-Coil Loudspeaker

Record Disc:

          The credit of recording sound on an ordinary disc goes to the American scientist, Thomas Alva Edison. He invented the phonograph in 1877.

            In 1887, the production of modern type of disc gramophone started. Commercial disc recording started in 1895.
Record Player

            If you see the disc with a magnifying glass you will observe wavy grooves on it. These wavy grooves are formed according to the intensity of vibrations of sound. Sound waves are recorded as an image in these grooves. After recording, the disc is rotated with a needle placed on the pin vibrations re produced in it ad thus the original sound gets produced. Today many developments have been made in the field of recording and reproduction of sound. Nowadays amplifiers are also used. Mechanical reproduction has been replaced by electrical pickup system. Long play and stereo records have also developed.

Tape Recorder:

          Tape recorders were started by Vladimir Paulsen in 1899. Sound is recorded on a plastic tape which remains wound like a reel in a cassette. Most of the cassette tapes are coated with iron oxide which is a magnetic material.

            In a tape recorder first of all electrical signals coming from a microphone are converts into magnetic signal. This is done by a small electromagnet which is called the recording head. Tape is passed through the had with the help of a motor. The iron oxide coated on it changes to a magnet by the electrical current generated due to sound waves. In this way sound is recorded on the tape in the from of magnetic field.
Magnetic Tape

         To listen to the sound recorded on the tape it is again passed through the head. The changing electric current due to the head resembles the electric current of the microphone at the time of recording. This electric current is amplified by an amplifier and then the original sound is prelude by the loudspeaker.

Compact disc:

Compact Disk

          The electric signals of a microphone are recorded on a compact disc by laser beam. Laser is also used for playback. The signals are recorded in the form of digits. We have the best reproduction of sound by this method. A compact disc measures only about 12 cm but in comparison to 30 cm long playing record its playing time is much more.

Friday, April 27, 2012

Cinematography Technology

        The moving pictures of cinema are based on the persistence of human vision. In fact, pictures do not move but still pictures appear on the screen one after the other. If we are looking at an object, then even after removing the object, its mage persists in our eyes for about 1/30 of a second and it gives an impression on that the object is there before our eyes. When pictures are shown very fast, one after the other on the screen, our mind is under the misapprehension that the pictures are moving. The second picture comes into the brain before the mental picture of the first is vanished. Then after a fraction of a second, a new picture appears which is lightly different from the previous one. In this way, the process continues and we get an illusion of moving pictures. The cinema pictures are shown at a speed of 24 scenes per second.

          In a cinema film, we have a long strip of thousands of still pictures, which is wound around a spool. The spool is mounted on a projector. The projector shows every picture or frame on a screen. Every second, 24 frames or pictures are projected on the screen so that the scene looks alive. Images on the film are recorded by a movie camera. This camera works like a still camera, the only difference is that it takes 24 pictures per second on the film. On one side of the film, sound signals are recorded. In the positive print of the film, sound and picture are both synchronized. This is called synchronization.

          The first cinema or movie was made by Thomas Alva Edison. This instrument was called kinetoscope, in which moving pictures were seen through a small hole.

          The credit of showing cinema film goes to the Lumiere brother’s of France. They made the first cinema projector by which film could be shown to a large number of audiences at a time.

          In March 1895, they showed their first short film with the help of a camera and projector in their factory. The world’s first cinema hall was built in France. Posters were pasted on the walls of the city on which photographs of the Lumiere brothers were printed and Lumiere’s Cinema’ was written in bold letters.

          Cinema was started in 1895 and for 34 years silent films were made. The fist talkie was made by the Warner brothers of America in 1927. The name of the film was The Jazz Singer. In the year 1930, colored films appeared. After that, cinema developed very fast. The side screen cinemascope films were made in the middle of this century. Today, we can see real scenes due to the techniques like Cinerama and technirama.
Kinetoscope

Cinema Projector
Lumiere Brothers

Thursday, April 26, 2012

Radar Technology

        The instrument used to detect the position and distance of an object is called radar. Bad weather, darkness and smoke do not affect the performance of radar. Radars are mostly used to determine the position, speed and distance of aircrafts and ships.

          An echo is produced when sound waves are reflected after striking an object. Similarly, radio waves produce an echo when they get reflected after striking a surface. The invention of radar is based upon the same principle. This is called the echo principle.

          The word RADAR stands for Radio Detection and Ranging. The first successful radar was developed by Robert Watson watt and his colleagues in 1930 in Britain.

          The transmitter of radar sends short pulses of high frequency from a rotating antenna. Theses pulses are reflected back after striking an object and are received by a receiver. The screen of the radar shows the position of the object. The time taken b the wave in going from the transmitter of radar to the object and then after reflection back to the receiver is determined. When this interval of time is multiplied by the velocity of light, we get double the distance of the object from the radar. The display unit fixed in the radar shows half of this distance. Besides aero plane and ship control, radar has played an important role in missile control, transport control, army, weather forecast, spacecraft control, etc.
Radar

Radio Technology

        Radio is one of the most effective means of sending messages, news, music, etc. to distant places. In this process, radio waves are used, which are a type of electromagnetic waves.

          The credit of inventing radio goes to Gugliemo Marconi of Italy. In 1901, Marconi succeeded in sending radio from England to Newfound land.

          The frequency of the radio waves used in radio broadcast lies between 150 kilohertz and 30,000 megahertz. The messages are transmitted through a transmitter which is connected to the radio station. Transmitter consists of instruments like microphone, modulator, amplifier, oscillator, antenna, etc. the person in the radio station speaks in front of a microphone, which converts sound waves into electrical signals. These signals are mixed with carrier waves in a modulator, amplified and transmitted.

          The modulation of radio waves is of two types; amplitude modulation and frequency modulation. The messages transmitted by transmitter are received by the aerial of our radio set. A radio set converts the electrical signals into sound and we hear the original programmed.

          Radio is used in telecommunications, navigation, etc. the radio services started in 1936 in our country. Today, there are more than 100 radio stations in our country.
Radio Waves

Photography Technology

        The technique of recording the image of an object on a photosensitive film with the help of a camera is called photography. In the beginning, metal or glass plates were used to records the images. Plastic roll films were developed in 1889. In the middle of the nineteenth century, several other chemical methods were invented for developing images in addition to Daguerretutype and collotype negative-positive methods. The negative-positive method is in the even today.

          All the cameras have a lens by which an inverted image of the scene is formed on the photo film. A photosensitive layer of silver bromide is coated on photo film. This is called exposing. After exposing, the film is developed in chemicals and then fixed. In this way, a permanent negative of a scene is made on the film. From this negative, prints of required size can be made on bromide paper using an enlarger.

          In colored photography, two types of films are used. The first one is color reversal film, on which color positive, slide or transparencies are made. The other one is color negative film, which is used of making color prints. Both of these films are sensitive to the three primary colors i.e. blue, green and red. In one color film, we have three layers of photo sensitive emulsion. The first layer is sensitive to blue color, second for green and third for red. Each emulsion layer absorbs or subtracts a definite amount of light. This is called subtractive process. The colored films are developed in a special developer and prints of desired size are made from them.
Digital Camera

Printing Technology

        Printing is a process in which a large number copies of text and pictures is produced on paper in a short time. This art was developed in the sixth century in China. After about 500 years, movable type was also invented in China. From China, this technique became popular in European countries. In the fifteenth century, Johannes Gutenberg of Germany developed the printing process in Europe. In 1476, William Caxton introduced the first printing press in London.

          Platen press, which used to print sheet by sheet, was replaced by rotary press. A rotary press continuously prints a paper roll. The printing which uses movable type is called letter press. In lithography, smooth plate is used. Text or picture is taken on a greasy surface, while the remaining part of plate is covered with grease repelling material. When greasy link is applied onto the plate, it adheres on the greasy parts only.

          The invention of computer has brought many improvements in printing. Nowadays, edition of text, printing and designing of page is done with the help of computers.

Work processing

          The type and designing of any text, newspaper or book can be done very fast and easily in required size in a work processor with the help of a computer. A word processor makes use f electronic system by which written matter can be edited on its own. We can alter the sequence of words and sentences, even delete or add words without typing the total matter again.

          Whatever you type on the keyboard gets displayed on the visual display unit VDU like a TV screen. Operators can do any change or correction in the text by using the editing key and movable pointer. Text gets stored in the memory of the word processor, which can be arranged accordingly by looking at the screen. Operators can store the text permanently on disk or tape, which can be used afterwards whenever needed. Word processor has a link with the electronic printer, by which a typed copy of text stored in memory comes out.

          Word processor also helps to set the text into pages. Line length, spacing, indentation, margins, etc. can be set according to will. When it is printed, the machine can arrange the text on its own, if a word a longer and is coming out of the line; the word processor brings this word in the next line and adjusts the spacing of the first line. In the same way, the size of the letters etc. can also be changed.
Letterpress Printing
Lithography Printing
Gravure Printing
Offset Printing Machine

Communication Developed Step by Step

        The word communication means exchange of information. Animals communicate with each other by special sounds. In olden times, man could communicate by shootings or blowing a horn or beatings a drum or flashing a light. Man gradually developed the art of talking and writing and started expressing his complex thoughts and information through language and writing. In the Mughal period, pigeons were used as carriers of messages. In the early 16th century, the postal system had begun. But the riders were used till 1830 for carrying letters and parcels to distant places.

          Communication took a new turn with the development of technology. In 1837, Cooke and Charles of England and Samuel Morse of America developed the electric telegraph. The information was sent I the form of electrical signal or codes through a cables by this instrument. The dots and dashles were used to represent the letters of the alphabets. In 1876 Alexander graham bell invented the telephone by voice over long distance through cables. In 1894, guglielmo Marconi of Italy invented the wireless telegraph by which messages could be sent across a long distance without wire. The efforts of these great scientists made it possible to send or receive messages from a part of the globe within no time.

The electric telegraph led to the development of the telex system while the wireless telegraph gave birth to the radio. Telephone networks have advanced very much. Besides messages, we can also send picture and document by fax.

Radio waves have played an important role in the communication systems. Radio waves are used in radio, telex, and television systems. Very short radio waves or microwaves are used to send messages across sea using satellites.
The development of microelectronics and computers have new dimensions in the field of communications. Computer can control thousands of messages simultaneously without any mistake.

          Books, newspapers, radio, television, cinema, etc. are other well known means of communications. Through these means, we can receive information from any part of the world within no time.
For Distance communication, nowadays communication satellites are used
The Fax machine can send and receive both worlds and pictures
In future everyone have a compact telephone

Wednesday, April 25, 2012

The Human New life

        Every new life starts as a single cell. After the sexual intercourse, when a sperm from the father’s semen enters the ovum of the mother, fertilization takes place. Pregnancy begins when a fertilized egg attaches itself to the lining of the uterus.

          During the first two months of pregnancy, the developing baby is called embryo. After this period until the birth 9 months, the developing baby is called a foetus. After two months, the foetus, though only about 2.5 cm in length can move its head, mouth, arms and legs. The child develops in about nine months in the womb. After nine months, a new child is born on earth.
Human Sperm
Embryo Stage
Mother's Womb

Tuesday, April 24, 2012

The Human Teeth

        Human beings have tow sets of teeth during their life time: primary teeth and permanent teeth. Primary teeth are also called deciduous or milk or baby teeth and begin to break through the gums after the age of six months. All the 20 primary teeth are in place by the child is three years old. The permanent teeth begin forcing out and replacing the primary teeth when the child is about six years old. All the 32 permanent teeth are in place usually when the person is in his/her early 20s.

          The 32 permanent teeth are arranged in pairs on each side of the upper and lower jaws. There are four types of teeth: incisors, canines, bicuspids or premolars and molars. The incisors are the eight front teeth, four in each jaw. The canines are four pointed teeth, one on each side of the incisors, two in each jaw. Next to the canines are two bicuspids, four in each jaw. Next to the bicuspids are six molars, three in each jaw.

          All the teeth have two parts: the crown and the root. The crown is the part of the tooth that is above the gum line. The root is below the gum. The part of the tooth at the gum line, where the crown and the root meet, is called the neck. The root is held light in the jawbone by a layer of bone tissue called cement.

          All true teeth are made up of three layers-------the outer hardest layer is called enamel, inside the enamel layer is dentine and the inner most layer is pulp. Dentine is like bone and its inside is called the pulp cavity that contains tiny blood vessels and nerves. The dentine is nourished by the pulp. 
Inside the tooth
Baby teeth
Permanent Teeth

The Human Ears

        We not only hear the sound with our ears but they also help us in maintaining the balance of the body. The ear is divided into three compartments -----the outer ear, the middle ear and the inner ear.

          Sounds are vibrations in the air. When a sound is made, its vibrations or sound waves travel all around. These waves strike with the outer ear and reach to the middle ear through a pipe. The ear drum or tympanic membrane is made to vibrate by these sound waves. Just behind the ear drum are three small bones, joined together. They are-------hammer, anvil ad stirrup. The three bones transmit these vibrations to cochlea. Cochlea is filled with a fluid in and contains thousands of the nerve cells. As cochlea vibrates, the fluid also vibrates and the nerve endings get excited. The impulses of the nerve endings are transmitted to the brain by auditory nerve. Brain analyses them and we hear the sound. Our ears can hear both feeble and loud noises. To keep the ears healthy, it is essential to get them cleaned form time to time. 
Inside the Ear

The Human Eye

        The eyes are a part of the sense organs that give human beings and most other animals the most accurate and detailed information about heir surroundings. Our eye is a sphere measuring about 2.5 cm in diameter. It rests in bony socket in the skull and can move in all directions due to the actions of the six ocular muscles.

          Eyes work on the principle of a photographic camera. The light rays form the object enters the pupil and are focused by the lens on the retina. Before the light enters the pupil, it passes through the cornea and aqueous humor. Lens forms an inverted reduced image of the object on the retina. From the image part of the eye, signals are sent to the brain by the optic nerves. The brain makes the correct and real image of the object and perceives depth and distance. The sensitive cells of the eyes are called rods and cones. The number of these cells is about 130 million. Rods are sensitive to light while cones are sensitive to colors. The two images produced by tow eyes are combined by the brain as one. The ability of the brain to form one image from the images of the tow eyes is called binocular vision.

Main parts of the eye

·       Lachrymal: this is the tear gland of the eye which produces tears. The tears clean the eyes.
·       Iris: it makes the pupil contract or dilates to control the amount of light that enters the eye.
·       Suspensory ligaments: lens is covered with a thin capsule which is connected to ciliary body by a soft ligament.
·       Lens: this is a soft and transparent convex lens which forms the image of the object onto the retina.
·       Vitreous humor: it is a jelly type transparent fluid.  
·       Aqueous humor: water like liquid.
·       Cornea: transparent part in the centre of the eye ball.
·       Choroids layer: black colored soft layer which stops the spread of light.
·       Retina: light sensitive screen on which image of the object is formed.
·       Optic nerve: this carries the information of the image to the brain.
Nature has provided us two eyes which give the correct estimate
of distance, depth and solid nature of the objects.
The Parts of Human Eye

The Human Respiratory System

        Respiration is a natural process in most living things. In this process, living beings change energy that is locked in molecules of digested food into a form that can be used by the cells. In the proce3ss of respiration, water ad carbon dioxide is produced. The body continuously takes in oxygen and releases carbon dioxide by this process. Intake of air is called inhalation and its expelling out is called exhalation. On an average, an adult breathes 15 to 17 times every minute.

          Human beings breathe in and out through nose and mouth. When air enters the nose, it is warmed and moistened before it goes to the lungs. In addition, the nose helps remove small particles of dirt and dust. This air goes into the lungs through the wind pipe. During the process of respiration, bulging of chest is a muscular action. This action is performed by both voluntary and involuntary muscles. In the process of respiration, mainly intercostals muscles and diaphragm take part. In deep breathing, shoulders, neck and muscles of stomach also take part.

          Lungs are the most important organs of respiratory system. There are two lungs, both of which lie in the air tight chest or thoracic cavity. The chest cavity and the lungs are covered with a membrane called pleura. Each lung is made of millions of alveoli. Lungs purify the blood coming from the heart by the oxygen which is inhaled and then the carbon dioxide of the blood is exhaled. After being purified, the blood goes back to the heart.

          A person’s berating is automatically controlled by the respiratory centre in the brain. This centre is sensitive to the amount of carbon dioxide in the blood. If there is an increase in carbon dioxide, such as during strenuous exercise, the respiratory centre sends more nerve signals to the muscles that control breathing. As a result, the person breathes faster.
The Human Respiratory System

The Human Excretory System

        The waste products and unwanted substances are removed from the body through excretory system. During the digestion of food, certain substances like ammonia, urea and uric acid are produced. Metabolic activities of the body produce wastes such as carbon dioxide and water. Since these waste products are poisonous in nature, they should be removed from the body.

          Water vapor and carbon dioxide come out of the body in the process of respiration. About 0.2 liter of carbon dioxide is given out every minute by a person. Ammonia, urea and uric acid reach the liver where ammonia is converted into urea. Urea and uric acid get mixed in the blood stream and go to the kidneys form the liver. The kidneys work as filters and separate out these substances form the blood. About 120 ml of blood of filtered by the kidney every minute. The whole blood is filtered by the kidneys about 30 times a day.

          The filtered substances do not contain urea and uric acid only but some other harmful substances also. All these substances are excreted from the body as urine. A person passes out about one liter of urine in a day.

          Our skin is also an important excretory organ. Water and salts come out from the skin in the form of sweat. About 0.7 liter of sweat along with small amount of salt is excreted from the human body each day through perspiration.
                           The Human Excretory System

The Human Digestive System

Alimentary Canal
·       Mouth
·       Pharynx or throat
·       Oesophagus or gullet
·       Stomach
·       Small intestine
·       Large intestine
·       Rectum
·       Anus

Food to a body is like fuel to the machines. Food is needed to
maintain body tissues and is a source of energy for all body functions. A complete food contains all the essential nutrients that are vital for the growth and working of the body. Food, normally, is in the solid state and it is made soluble and absorbable by the chemical reactions of enzymes and digestive juices. The place where food is digested is called digestive tract and from where chemical substances are released, is called digestive gland. They together make the digestive system.

Taste:

 The pleasure of life lies in the different tastes of food. There are granular lumps on the upper surface of our tongue. These are called taste buds. Different tastes buds are connected to the brain by nerve cells which carry the information of taste to the brain. Taste buds are of four kinds which identify sweet, bitter, sour and salty tastes. In the figure below are shown different taste buds and their locations on the tongue.

How food gets digested:

Digestion of food begins in the mouth itself. Chewing makes food soft and breaks it into small pieces. The saliva in the mouth helps break down some carbohydrates into sugar. Saliva also makes the food slippery so that it can slide down the throat or oesophagus easily. A wave like muscle contraction called peristalsis pushes the food down to the stomach. Churning of the stomach changes the food into a semi liquid mass called chime. At this time gastric juices and acids such as hydrochloric acid start digesting the food and help to kill the bacteria in the food. Liquid food now goes int o the small intestine. Here some more enzymes are added to the food most of the food is broken down in the small intestine into its simplest form-----sugar, amino acids and fat. It takes about five hours. The nutrients of the food are absorbed by millions of tiny finger like projections called villi. From there the nutrients are absorbed into the blood and are transported to every cell.

          From the small intestine food goes to the large intestine. The small intestine is about 6.5m long while large intestine is 1.8m long. As it passes into the large intestine, water is removed and the waste product is passed out of the body as faeces through the anus. The faeces contain undigested food, cell, bile, salt ad spleen salts. 
The Digestive System
                                                   Taste Buds and The Tongue

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