Chapter 13

1. Chapter 13 Sound

2. Section 1

3. Electromagnetic waves • made by vibrating electric charges and can travel through space. • Electric and magnetic fields • related forces operate even in empty space • Moving electric charge creates magnetic field • Changing magnetic fields create changing electric fields and vice versa. • Electromagnetic waves • produced when an electric charge is vibrating • Vibrating electric charges are surrounded by vibrating electric and magnetic fields

4. Properties of Electromagnetic fields • carry radiant energy • as frequency increases, wavelength decreases • Frequency • number of vibrations per second • measured in hertz • Wavelength • is the distance from one crest to another • measured in meters • Wave speed • the vacuum of space, 300,000 km/s • electromagnetic waves slow as they travel through matter

5. Waves and particles • Difference is still not clear • Light can behave as a particle or wave • Know as duality • Photon • Particle of light whose energy depends on frequency • All particles can behave like a wave

6. Section 2

7. Electromagnetic spectrum • Entire range of electromagnetic wave frequencies • Radio waves • low-frequency electromagnetic waves with wavelengths from less than a cm to about 1000 m • Microwaves • radio wave lengths of about 1 to 10 cm • Radar • radio waves bounced off an object to determine its speed and location • Magnetic Resonance Imaging (MRI) • radio waves produce an image of inside the body

8. Infrared waves • slightly higher frequency than radio waves • people feel it as thermal energy or warmth • Visible light • wavelengths between ~390 to 770 billionth of a meter • can be seen with the eye • Ultraviolet waves • Have frequencies slightly higher than visible light; can damage skin • Ultraviolet light • can kill bacteria • can be absorbed by some fluorescent materials and released as visible light • Ozone layer • absorbs most of the Sun’s harmful ultraviolet waves.

9. X rays and gamma rays • ultra-high-frequency electromagnetic waves that can travel through matter, break molecular bonds & damage cells • X rays • used to provide images of bones and to examine suitcases at airports without opening them. • Radiation therapy • used to kill diseased cells

10. Section 3

11. Radio transmission • radio converts electromagnetic waves into sound waves • Carrier wave • specific frequency which radio station is assigned • AM radio • broadcast by varying amplitude of carrier wave • frequencies range from 540 to 1,600 thousand vibrations per second • FM radio • transmit by varying frequency of carrier wave • frequencies range from 88 million to 108 million vibrations per second

12. Television • sounds and images changed into electronic signals broadcast by carrier waves • Audio • sent by FM radio waves • Video • sent by AM signals • Cathode-ray tube • A sealed vacuum chamber with a coated screen that receives electron beams to provide images

13. Telephones • microphone converts sound waves into electrical signal • Cell phone • electrical signal creates a radio wave that is transmitted to and from a microwave tower • Cordless phone • transceiversends one radio signal & receives another at different frequency from base unit • Pagers • radio receiver on which a message is left

14. Communication satellites • high frequency microwave signal is transmitted to a satellite • satellite amplifies it and returns it to Earth at a different frequency • Satellite telephone systems • mobile phones transmit radio signals to a satellite • satellite relays them back to a ground station that passes the call into the telephone network • Television satellites • uses microwaves rather than longer-wavelength radio wave • ground receiver dish focuses the microwave beam onto an antenna

15. Global positioning system • system of satellites, ground stations, and receivers that provide information about the receiver’s location on or above the Earth’s surface • G.P.S.