The telephone works on some basic principles involving the fields of electricity, electromagnetic induction and acoustics; converting sound waves into electrical energy and vice versa.
Whether you are listening or talking the same technology and principles are used; when you talk into the mouthpiece a thin metallic or plastic foil just beneath it starts vibrating due to the speech sounds. Beneath the foil is an electrode connected to a wire carrying an electric current; the vibrating foil introduces changes in the voltage and these changes are then carried forward as electric pulses.
When the listener hears your voice at the other end the entire process repeats itself in the reverse; the electric pulses affect the magnetic field of the receiver at the other end and the foil starts vibrating and picks up the pulses as they had been introduced at the origin resulting in a counter conversion of the electric energy back into acoustic energy or sound waves. The electric current flows into your phone set from the phone company by way of two copper wires ensuring that your phone does not stop working even though the power in your house may have gone off.
In a cell phone however the required voltage is provided by the battery in it which transmits the electric pulses in the form of radio frequency to the nearest cell phone tower which in turn transmits the signals to the cell phone exchange then to the main telephone exchange from where the process works in the reverse till the call reaches the receiver.
A telephone has two main parts to it, one is the 'Transmitter' and the other is the 'Receiver'.
The transmitter is placed behind the mouthpiece of the instrument. It has an eardrum which is thin, round metal disc called a diaphragm. This diaphragm vibrates when the sound waves strike it. This vibration takes place at different speed levels. This depends on the air pressure caused by the voice. Behind this metal disk there is a container filled with tiny grains of carbon. Subsequently, the diaphragm presses on these carbon grains. This pressure varies as the diaphragm vibrates, due to sound waves. The louder the sound the harder is the diaphragm pushed.
The receiver is known as an electric mouth. In the receiver there is a diaphragm located which has two magnets located at the edge of it. One magnet is an electromagnet which consists of an electric wired coil which is wound around it. If the vocal levels are high, the electric force passed through this wire is stronger and attracts the diaphragm towards it. The diaphragm vibrates depending on the vocal levels. Since the diaphragm keeps moving in and out it pushes the air around it, this air sets up the sound waves. These waves are what strike the ear of the listener.
The principle of how the telephone operates is rather pretty simple. The general description of it is that sound signals are converted into electrical signals through the microphone at a certain location. The electrical signals are transmitted to its destination through a network of electrical wirings. Once the signals reach their destination, they are converted back to sound waves through a receiver.
Although many are credited for the invention of the telephone it was Alexander Graham Bell who was recognized for its invention mainly because he was the first to file a patent for the device. But the British government some ten years ago recognizes Antonio Meucci for educational purposes as the first inventor of the telephone.
A simple telepphone system would consist of three basic elements:
1.A device located at each subscriber that converts sound signals to electrical signals or vice - versa.
2. A central switching facility that interconnects all the subscribers.
3. A network of electrical wirings that connect all the subscribers to the central switching facility.
How the Telephone Works
When a person speaks into a telephone, the sound waves created by his voice enter the mouthpiece. An electric current carries the sound to the telephone of the person he is talking to. A telephone has two main parts: (1) the transmitter and (2) the receiver.
The Transmitter of a telephone serves as a sensitive "electric ear." It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum." The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker's voice.
Behind the diaphragm lies a small cup filled with tiny grains of carbon. The diaphragm presses against these carbon grains. Low voltage electric current travels through the grains. This current comes from batteries at the telephone company. The pressure on the carbon grains varies as sound waves make the diaphragm vibrate. A loud sound causes the sound waves to push hard on the diaphragm. In turn, the diaphragm presses the grains tightly together. This action makes it easier for the electric current to travel through, and a large amount of electricity flows through the grains. When the sound is soft, the sound waves push lightly on the diaphragm. In turn, the diaphragm puts only a light pressure on the carbon grains. The grains are pressed together loosely. This makes it harder for the electric current to pass through them, and less current flows through the grains.
Thus, the pattern of the sound waves determines the pressure on the diaphragm. This pressure, in turn, regulates the pressure on the carbon grains. The crowded or loose grains cause the electric current to become stronger or weaker. The current copies the pattern of the sound waves and travels over a telephone wire to the receiver of another telephone.
The Receiver serves as an "electric mouth." Like a human voice, it has "vocal cords." The vocal cords of the receiver are a diaphragm. Two magnets located at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that constantly holds the diaphragm close to it. The other magnet is an electromagnet. It consists of a piece of iron with a coil of wire wound around it. When an electric current passes through the coil, the iron core becomes magnetized. The diaphragm is pulled toward the iron core and away from the permanent magnet. The pull of the electromagnet varies between strong and weak, depending on the variations in the current. Thus, the electromagnet controls the vibrations of the diaphragm in the receiver.
The electric current passing through the electromagnet becomes stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker's speech pattern. As the diaphragm moves in and out, it pulls and pushes the air in front of it. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.
Materials for a modern phone are easily accessible, they include a speaker, for taking sound, a microphone, for giving sound, a touch-tone keypad and frequency generator for dialling up a phone number, a duplex coil, so you don't have to listen to yourself, a hook switch, for connecting and disconnecting your phone to the phone network, and a ringer, to let you know your being called. All this is connected to 2 copper wires than run out of your house to your local entrance bridge. An entrance bridge is a box located in most neighbourhoods which collect and gather telephone wires from houses and links them with the telephone company. For every telephone line that you have, a pair of copper wires link to your local entrance bridge. At the telephone station, your telephone signal is connected to the number (or rather frequency) that you dialled, then connected to the nearest telephone station to the phone number which you dialled, it is then connected to the place you called by a pair of copper wiring. The telephone at the other end of the line rings in response of being connected. For long distance calls, your telephone signal is connected to a satellite and sent back down to the nearest telephone station of your wish, or otherwise connected through underground wiring.
Remember in the old movies you see the operators pulling and connecting plugs as fast as they can in the telephone station? Today, instead of operators, we have electronic switches.
In response to you turning on your phone (or picking it up from the holder if it's not wireless), the telephone station will play a tone so that the caller is aware that the phone is working.
A telephone works in which a event a thin metallic coat vibrates towards an electrode (a conductor) when a sound is made into the microphone. The sounds result in a variation of voltage which is translate from acoustic to electric energy, when the electric energy reaches the other end of the phone line it is converted back into acoustic energy.