| Subject: HMWK Done!! |
Author:
Jian
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Date Posted: 10:37:06 07/02/01 Mon
In reply to:
Caladia
's message, "~sighs and puts her pencil down, rubbing her eyes~" on 07:03:54 03/28/01 Wed
The Telephone:
The telephone was invented by Alexander Grandbell:
ALEXANDER GRAHAM BELL
1847-1922
Alexander Graham Bell was born on March 3, 1847 in Edinburgh, Scotland, the son of Alexander Melville Bell and Eliza Grace Symonds, daughter of a surgeon in the Royal Navy. His mother, who was a portrait painter and accomplished musician, began to lose her hearing when Graham (a name that was used by his family and close friends) was twelve. His father had a world wide reputation as a teacher and author of textbooks on correct speech, and as the inventor of "visible speech," a code of symbols which indicated the position and action of the throat, tongue and lips in uttering various sounds. Melville’s Visible Speech helped to guide the deaf in learning to speak and Graham became an expert in its use for that purpose.
Graham and his two brothers assisted Melville in public demonstrations in Visible Speech, beginning in 1862. At the same time he enrolled as a student-teacher at Weston House, a boys’ school near Edinburgh where he taught music and speech in exchange for being a student of other subjects. A year later he became a full-time teacher at the University of Edinburgh while studying at the University of London.
In 1866 Bell carried out a series of experiments to determine how vowel sounds are produced. He combined the notes of electrically driven tuning forks to make vowel sounds which gave him the idea of "telegraphing" speech. In 1870 his brothers died of tuberculosis and his family moved to Brantford, Ontario, Canada to a healthier climate. A year later Graham moved to Boston where he opened a school for teachers of the deaf and in 1872 became a professor at Boston University.
Bell’s interest in electricity continued and he attempted to send several telegraph messages over a single wire at one time. Lacking the time and skill to make the equipment for these experiments he enlisted the help of Thomas A. Watson from a nearby electrical shop. The two became fast friends and worked together on the tedious experimentation to produce sounds over the "harmonic telegraph." It was on June 2, 1875, while Bell was at one end of the line and Watson worked on the reeds of the telegraph in another room that he heard the sound of a plucked reed coming to him over the wire.
The next day, after much tinkering, the instrument transmitted the sound of Bell’s voice to Watson. The instrument transmitted recognizable voice sound, not words. Bell and Watson experimented all summer and in September, 1875, Bell began to write the specifications for his first telephone patent.
The patent was issued on March 7, 1876. The telephone carried its first intelligible sentence three days later in the rented top floor of a Boston boarding house at 109 Court Street, Boston.
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.
*puts down her quill* "Ahhh done at last I hope I didn't go overboard!"
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