# Mechanics of the Telephone

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Learn about the parts of a basic telephone, and how they work: microphones, earpieces, switches, and wires. See how much you've learned, and take a quiz at the end of this lesson.

## What is a Telephone?

The phone rings, and you answer it without a thought. It's your grandma, and you have a nice conversation about knitting. But do you ever stop to think about how you're able to do that at all? When the first audio recording was made, people thought it was magic and were scared. Yet talking long distances seems perfectly normal to us these days. Today we're going to address that, and learn how a basic telephone works.

A telephone is a system that turns sound waves into electrical signals so that sound can be transmitted over long distances. Telephones are used to transmit voice conversations, allowing people to talk to each other when they're not all in the same place. Telephone conversations can be between two people, which is the most common case, or between multiple people at once. The telephone was invented in 1876 by Alexander Graham Bell.

## How Do Telephones Work?

Basic, old-fashioned telephones are very simple devices. They only contain a few parts: a microphone, an earpiece, a switch in the base of the phone, and wires.

When you speak into a phone, you're actually speaking into a microphone. A microphone contains a magnet mounted on a moving surface that vibrates with the sounds that you project into it. When you speak into the microphone, the magnet vibrates back and forth. When a magnet moves near an electrical wire, electricity is created in that wire.

So when you talk into the microphone, signals that match the vibration created by a voice are sent down the electrical wire. Then, when those signals are sent to another person's earpiece, which is really just a microphone in reverse, they cause the magnet to move up and down in the same pattern. The earpiece is connected to a diaphragm that also moves up and down, re-creating the sound and allowing the listener to hear what the speaker has said.

Phones also contain switches, which connect you and disconnect you from the telephone line, so sound isn't always being received by the phone. And they do, of course, contain wires, too, because this is how the signal is transmitted all the way to the other person's phone; phones also require exchanges with systems that can make sense of the phone numbers you input, and connect you to the correct place.

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