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# Mechanical Wave

## Introduces waves in matter and how they transfer energy.

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Telephone Magic

### Telephone Magic

Credit: Dominik Syka
Source: http://www.flickr.com/photos/dominiksyka-photography/4334590250

The phone rings. You answer it and hear the voice of a friend. Your friend’s voice began as sound waves, but they traveled to your phone as electrical signals. How does your phone turn the signals back to sound waves that you can hear? It seems almost magical.

#### The Back Story

• The telephone contains an electromagnet that is responsible for the magic. An electromagnetic is a magnet created by electric current flowing through a coil of wire that is wrapped around a bar of iron.
• Credit: David Blaikie
Source: http://www.flickr.com/photos/nikonvscanon/715473620/

Audio headphone also use electromagnets, but are able to produce very high quality sound waves [Figure2]

• For an overview of how a telephone works, including the role of the electromagnet, watch this very brief video:

#### Show What You Know

1. Describe the basic parts of a telephone.
2. A telephone has two diaphragms. What are they, and where are they located? What human body structure does each diaphragm resemble in terms of function?
3. Sound waves are mechanical waves. These are waves that travel through matter. When you speak, sound waves travel through the air by making air molecules vibrate. How are these vibrations changed into electrical signals by the telephone?
4. Where do the electrical signals go after they leave your telephone?
5. What happens to the electrical signals when they reach the phone of the person you are calling? How are they changed back to sounds?

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