1. DAILY QUESTION April 27, 2009 1. What is atmospheric transmission?

2. Agenda 4/27/09  Daily Question  Check-in: 18-1 Worksheet  Ch 18 Section 2 Notes  Brain Pop – Telephones and Cell Phones Assignments: 1. Cell Phone Use Worksheet

3. Telephones  Uses an electret microphone An electrically charged membrane that is mounted over an electrect, which is a material that has a constant electric charge  Uses a speaker cone A coil of wire that is fastened to a thin membrane

4. How a telephone works  The sound waves from your voice are transformed by the microphone into an analog electrical signal. A speaker converts the analog electrical signal back to sound waves. Sound waves – analog electrical signal – sound waves microphonespeaker

5. Brain Pop - Telephones

6. Telephone messages over short distances  Signal is sent along wires to local stations Called physical transmission  Cables are strung along poles Fiber optic cables and laser diodes (causes light to brighten and dim)

7. Telephone messages over longer distances  Sent through the atmosphere using microwave radiation Called atmospheric transmission

8. Computers help route calls  Used to find most direct route Physical transmission Atmospheric transmission Both

9. Cell Phones  Cellular phones are a small radio transmitter/receiver Transceiver  Communicate with antennas Area covered by antenna is called a cell Phone switches from antenna to antenna  Out of range, no service

10. Brain Pop- Cell Phones

11. Cell Phone Use Graphs