1. Communicating by Wire The Telephone

2. The telephone was one of the many devices that was invented by accident. The telephone was one of the many devices that was invented by accident. Alexander Graham Bell was a speech teacher who was working on ways to send several telegraph messages at the same time over one wire. Alexander Graham Bell was a speech teacher who was working on ways to send several telegraph messages at the same time over one wire.

3. He knew that if a musical note of a certain frequency was played near a group of tuning forks, only the tuning fork tuned to that frequency would vibrate. He knew that if a musical note of a certain frequency was played near a group of tuning forks, only the tuning fork tuned to that frequency would vibrate. Bell thought that he could send several musical notes over the same wire, several tuning forks at the other end could sort out the notes. Bell thought that he could send several musical notes over the same wire, several tuning forks at the other end could sort out the notes. Although Bell was never successful in making this system work, it is the same principle used in many electronic communication circuits today. Although Bell was never successful in making this system work, it is the same principle used in many electronic communication circuits today.

4. In 1875, Bell’s assistant, Thomas Watson, was hanging metal strips to make musical notes while Bell was in another room listening to a receiver. In 1875, Bell’s assistant, Thomas Watson, was hanging metal strips to make musical notes while Bell was in another room listening to a receiver. One of the metal strips accidentally got stuck and acted as a diaphragm, picking up the jingling noise of the other strips. One of the metal strips accidentally got stuck and acted as a diaphragm, picking up the jingling noise of the other strips. Bell heard the jingling noises and realized what had happened. Bell heard the jingling noises and realized what had happened.

5. How a Telephone Works The principle of the diaphragm is basic to the operation of the telephone. The principle of the diaphragm is basic to the operation of the telephone. Simple telephones use a thin metal disk as a diaphragm. When you speak into the mouthpiece of a modern telephone, the diaphragm vibrates. Simple telephones use a thin metal disk as a diaphragm. When you speak into the mouthpiece of a modern telephone, the diaphragm vibrates. It pushes against a container holding carbon granules. It pushes against a container holding carbon granules. As the granules are packed more tightly by the diaphragm’s pushing on them, there electrical resistance goes down. As the granules are packed more tightly by the diaphragm’s pushing on them, there electrical resistance goes down.

6. As the diaphragm relaxes the pressure on the granules, the electrical resistance goes up. As the diaphragm relaxes the pressure on the granules, the electrical resistance goes up. If a voltage is applied to the container holding the carbon granules, then the varying resistance changes the current flowing through the circuit. If a voltage is applied to the container holding the carbon granules, then the varying resistance changes the current flowing through the circuit. A varying electrical current that exactly represents speech is thus generated. A varying electrical current that exactly represents speech is thus generated. The telephone receiver earpiece has a diaphragm made out of a metal that is attracted to a small electromagnet. The telephone receiver earpiece has a diaphragm made out of a metal that is attracted to a small electromagnet.

7. The current flowing through the electromagnet is the varying current produced by the mouthpiece of the other telephone. The current flowing through the electromagnet is the varying current produced by the mouthpiece of the other telephone. As the current varies, the attraction of the electromagnet for the diaphragm also varies. As the current varies, the attraction of the electromagnet for the diaphragm also varies. This causes the diaphragm to vibrate in exactly the same way the mouthpiece diaphragm first did. This causes the diaphragm to vibrate in exactly the same way the mouthpiece diaphragm first did. The vibrating diaphragm moves the air turning the varying electric current back into sound. The vibrating diaphragm moves the air turning the varying electric current back into sound.

8. The difference between the telegraph and the telephone is that the telegraph operates using on off pulses of electric current, while the telephone uses a smoothly varying continues current. The difference between the telegraph and the telephone is that the telegraph operates using on off pulses of electric current, while the telephone uses a smoothly varying continues current. Telegraph signals could only be sent and received by someone who had been trained to understand the Morse Code. Telegraph signals could only be sent and received by someone who had been trained to understand the Morse Code. A telephone could be used by anyone without formal training. A telephone could be used by anyone without formal training.

9. The Telephone System The growth of the widespread telephone use was slow at first. The growth of the widespread telephone use was slow at first. The rate increased as the telephone network grew. The rate increased as the telephone network grew. At first, telephones were not as useful as they are today because there were only a few others that could be called. (How useful would a telephone be if it could only call two other people) At first, telephones were not as useful as they are today because there were only a few others that could be called. (How useful would a telephone be if it could only call two other people)

10. Telephone networks were started only within towns or small areas. Telephone networks were started only within towns or small areas. Communication with other distant towns was not possible. Communication with other distant towns was not possible. As the number of telephones grew, networks grew to connect more people over wider areas. As the number of telephones grew, networks grew to connect more people over wider areas. This made having a telephone more desirable, further increasing the number of telephones. This made having a telephone more desirable, further increasing the number of telephones.

11. By 1900, there were about one million telephones in use in the United States. By 1900, there were about one million telephones in use in the United States. When Bell died in 1922, all 13 million telephones in Canada and the United States were shut off for one minute in tribute. When Bell died in 1922, all 13 million telephones in Canada and the United States were shut off for one minute in tribute. In the United States today, there are more than 200 million telephones. In the United States today, there are more than 200 million telephones. Any phone can be used to communicate with any part of the world almost instantly. Any phone can be used to communicate with any part of the world almost instantly. There are about 1.3 billion telephone conversations each day in the United States. There are about 1.3 billion telephone conversations each day in the United States.