Here are the answers to your questions: 1. The three main parts of a phone are the transmitter, receiver, and dialing mechanism. 2. During a phone call, sound waves cause a metal disk in the transmitter to vibrate, transforming sound into an electronic signal. The receiver uses a speaker to transform the electronic signal back into sound. 3. Electromagnetic waves consist of changing electric and magnetic fields that can carry signals over long distances. A changing magnetic field produces a changing electric field and vice versa. 4. For radios, an audio signal is combined with a carrier wave and transmitted via electromagnetic waves to antennas. The radio separates the signal from the carrier wave. For TV, video and audio signals

2. tele - at or over a distance; distant
phone - sound

3. 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.

5. How do
telephones
work?
• http://www.youtube.com/watch?

6. • 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.

8. – 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/wat
ch?
feature=player_detailpage&v=
cfXzwh3KadE#t=17s

9. 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.
Electromagnetic Spectrum: Radio Waves
http://www.youtube.com/watch?
feature=player_detailpage&v=al7sFP4C2
TY#t=17s
The Electromagnetic Spectrum Song
http://www.youtube.com/watch?
v=bjOGNVH3D4Y

10. Amplitude and Frequency Modulation

11. 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

12. 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.

14. 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?