1. Waves?
Chapter 17 Notes

2. The Nature of Electromagnetic Waves
Electromagnetic waves are transverse waves that transfers changing electrical and magnetic energy.
An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light.
Charged particle surrounded by a magnetic field
electromagnetic radiation - energy transferred through space by electromagnetic waves
speed of electromagnetic waves = 300,000,000 m/sec
Chapter 17

3. The Nature of Electromagnetic Waves
Many properties of electromagnetic waves can be explained by a wave model. However, some properties are best explained a particle model.
Wave properties - polarization allows waves that vibrate in only one direction to pass through
Polarized filter demo
Chapter 17

4. The Nature of Electromagnetic Waves
Particle properties - photoelectric effect. When a beam of light shines on some substances, it causes tiny particles called electrons to move. Sometimes the particles move so much they are knocked out of the substance.
The photoelectric effect can be explained only by thinking of light as a stream of tiny packets, or particles, of energy - called a photon.
Photoelectric effect demo
Chapter 17

5. Waves of the Electromagnetic Spectrum
All electromagnetic waves travel at the same speed in a vacuum, but they have different wavelengths and different frequencies
Speed = Wavelength X Frequency
ROYGBV
Chapter 17

6. Waves of the Electromagnetic Spectrum
Electromagnetic Spectrum – the complete range of electromagnetic waves placed in a particular order: radio waves - infrared rays - visible light - ultraviolet rays - x rays - gamma rays
longest wavelength & lowest frequency to shortest wavelength & highest frequency
Visible light: ROYGBV
Chapter 17

7. Waves of the Electromagnetic Spectrum
Radio waves
longest wavelength, lowest frequencies.
broadcast waves:
Longer wavelength
radio and TV.
Appliance converts waves into sound that comes out of speakers
Chapter 17

8. Waves of the Electromagnetic Spectrum
microwaves (Radio Wave)
shortest wavelength radio waves, highest frequencies.
more than just ovens, i.e. cell phones
water molecules absorb energy and get hot
radar - microwaves used to measure speed and location. Similar to sonar
RADAR - RAdio Detection And Ranging - microwaves used to measure speed and location. Similar to sonar
Chapter 17

9. Waves of the Electromagnetic Spectrum
Infrared Waves
shorter wavelength than radio waves -higher frequency (more energy) than radio
given off as heat
heat lamp & thermogram
visible light
rainbow
small part of electromagnetic spectrum
white light is all wavelengths
Chapter 17

10. Waves of the Electromagnetic Spectrum
Ultraviolet Rays
carry more energy than visible light
Sunburn
kill bacteria
Small doses beneficial vitamin D
X-Rays
short wavelengths - high frequency - carry more energy
can penetrate most matter
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11. Waves of the Electromagnetic Spectrum
Gamma rays
shortest wavelengths - most energy
produced by radioactive substances
highly penetrating
can cause cancer
Some medical uses
Food Irradiation?
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12. Producing Visible Light
Illuminated - object that can be seen because it reflects light
Luminous - an object that gives off its own light
Bioluminescence - organisms that produce their own light. Fireflies. Some jellyfish.
Common types of light bulbs include incandescent, tungsten-hologen, fluorescent, vapor, and neon lights.
Chapter 17

13. Producing Visible Light (con’t.)
incandescent lights - filament gets hot and emits all colors of spectrum
ordinary - not very efficient 10 %
tungsten-halogen – hotter/whiter
florescent lights - tube contains gas, coated on inside with powder
produces UV  fluoresces powder  visible light
last longer use less electricity
less infrared / less heat
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14. Producing Visible Light (con’t.)
vapor lights - street lighting
neon or argon with sodium (yellow) or mercury (blue) vapor
Efficient
neon lights - pass electric current through gas (electric discharge through gases)
Neon  red
Different gasses produce different colors.
Argon and mercury  greenish-blue
Helium  pink
Krypton  pale violet
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15. Wireless Communication
Transmission antennas send out, or broadcast, radio waves in all directions,. Radio waves carry information from antenna of a broadcasting station to the receiving antena of your radio or television.
At broadcasting station, music and speech are converted from sound to electronic signals.
Chapter 17

16. Wireless Communication
The electronic signals for AM broadcasts are then converted into a pattern of changes in the amplitude of a radio wave.
Sound signals are carried by varying either the amplitude (AM) or the frequency (FM) of radio waves pg. 595
AM - long wavelengths easily reflected by ionosphere.
Can broadcast over long distances especially at night.
Chapter 17

17. Wireless Communication
FM - frequencies much higher than AM.
Are not reflected by ionosphere.
Do not travel as far as AM.
Produce a better sound quality. TV
AM for pictures FM for sound
Radio Spectrum
Kilohertz – kHz
Megahertz – MHz
VHF
UHF
Chapter 17

18. Wireless Communication
Cellular telephones - transmit and receive signals using high frequency microwaves (radio waves.)
Wireless communication timeline pg.597
Communication satellites - radio waves are sent from the Earth up to the satellite, which relays the waves to other receivers on Earth.
satellite telephone
satellite TV
GPS (3 satellites)
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