tele - at or over a distance; distantphone - sound

Telephones• Invented by Alexander Graham Bell in 1876• Modern phones use 3 of the same parts as Bell’s: a

transmitter, a receiver, and a dialing mechanism– Transmitter: Sound waves cause a metal disk in the

microphone to vibrate, transforming the sound into an electronic signal.

– Receiver: located in the earpiece of a telephone. It uses a speaker to transform the electronic signal back into sound. A speaker is made up of an electromagnet and a thin metal disk.

– Dialing Mechanism: The tones act as signals to the electronic circuits in the switching network. Push button and dial phones use different tones to connect calls.

How do telephones

work?

• http://www.youtube.com/watch?feature=player_detailpage&v=Oc-kBiWsMik#t=9s

• Analog Sound Recording: When you play a record, a needle runs along a spiral groove. The wavy pattern of the groove varies the same way as the sound waves. The needle’s movement moves a tiny magnet that induces an electric current.

• Digital Sound Recording: CDs contain microscopic holes, called pits. The level areas between the pits are called flats. The arrangement of pits and flats is a code. Each piece of this code represents the sound at one instant.

– a wave that consists of moving, or changing electric and magnetic fields.

• Electronic signals can be carried over long distances by electromagnetic waves.

• If a magnetic field is changing, a changing electric field will form. The changing electric field that is formed then produces a changing magnetic field. The electric and magnetic fields will keep producing each other over and over again.

http://www.youtube.com/watch?feature=player_detailpage&v=cfXzwh3KadE#t=17s

Electromagnetic Spectrum: Radio Waveshttp://www.youtube.com/watch?

feature=player_detailpage&v=al7sFP4C2TY#t=17s

The Electromagnetic Spectrum Songhttp://www.youtube.com/watch?

v=bjOGNVH3D4Y

Waves are described in terms of amplitude and frequency. The amplitude is the height from the center line to a crest or trough. The frequency of a wave is the number of waves passing a given point each second.

Amplitude and Frequency Modulation

Radio

• Transmission: Begins at a radio station, sound is transformed into an electronic signal. This current is an analog signal that represents the sound waves. The signal is then sent to a transmitter which amplifies the signal and combines it with a carrier wave.

• Reception: Radio antennas receive electromagnetic waves from the radio station. The carrier wave has a specific frequency. Your radio amplifies the audio signal and separates it from the carrier wave.

http://www.youtube.com/watch?v=gLMC5R5Me9c

Television

• Transmission: The signals are usually sent from transmitting antennas. Communications satellites are also used to relay television signals. A communications satellite orbits Earth, always staying above the same point on the ground. These satellites receive signals from one part of the planet and transmit them to another.

• Reception: Each television contains a receiver that accepts video and audio signals. The carrier wave for each television station is at a specific frequency. You tune in the frequency by selecting a channel. Your television amplifies the signal and separates it from the carrier wave.

1. What are the three main parts of the phone?

2. How is sound transmitted and received during a phone call?

3. What are electromagnetic waves?

4. How is information transmitted to radios and television?