How a telephone works
In this essay I would explain how a person can talk to the phone and another person can hear him\her talking. 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, the transmitter and the receiver.
Firstly about the transmitter, a transmitter of a telephone is like a sensitive electric ear. It placed behind the mouthpiece of the phone. The transmitter has the 14 eardrum like human ears. The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves hit the diaphragm and make it vibrate. The diaphragm vibrates at any speeds, depending on the variations in air pressure caused by the unstable 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 positioned at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that always 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.
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 hit the ear of the listener and he hears the words of the speaker.
Mazniza binti Haji Brahim
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