Waves?

1. Waves? Chapter 17 Notes

2. The Nature of Electromagnetic Waves • Electromagnetic waves are transverse waves that consist of changing electric and magnetic fields • Electric current is surrounded by a magnetic field • electromagnetic radiation - energy transferred by electromagnetic waves • speed of electromagnetic waves = 300,000,000 m/sec Chapter 17

3. Light has many properties of waves, but can also act as though it is a stream of particles • wave properties - polarization allows waves that vibrate in only one direction to pass through • particle properties - photoelectric effect. When a beam of light shines on some substances, it causes tiny particles called electrons to move • light can travel through a vacuum Chapter 17

4. Waves of the Electromagnetic Spectrum • All electromagnetic waves travel at the same speed, but they have different wavelengths and different frequencies • radio waves - infared rays - visible light - uv rays - x rays - gamma rays • ROYGBV Chapter 17

5. radio waves - longest wavelength, lowest frequencies. Radio converts waves into sound that comes out of speakers • microwaves - shortest wavelength, highest frequencies. Water molecules absorb energy and get hot • radar - microwaves used to measure speed and location. Similar to sonar Chapter 17

6. infrared waves - given off as heat • magnetic resonance imaging (MRI) - • uses magnetic waves to create pictures of internal body organs • muscles and • soft tissues • visible light - rainbow. Small part of electromagnetic spectrum Chapter 17

7. ultraviolet rays • carry more energy than visible light. • Sunburn, • kill bacteria. • Small doses beneficial vitamin D • x rays - short wavelengths. • Carry more energy. • Can penetrate most matter. Chapter 17

8. Gamma rays - • shortest wavelengths. • Produced by radioactive substances. Highly penetrating. • Can cause cancer. • Some medical uses. • Food irradiation - pg. 547 Questions 1-3 Chapter 17

9. Producing Visible Light • illuminated - object that can be seen because it reflects light • luminous - an object that gives off its own light • incandescent lights - filament gets hot and emits all colors of spectrum • not very efficient 10 % • florescent lights - tube contains gas coated on inside with powder • last longer use less electricity Chapter 17

10. Producing Visible Light (con’t.) • neon lights - pass electric current through gas. Different gasses produce different colors. • Sodium vapor lights - street lighting • Bioluminescence - organisms that produce their own light. Fireflies. Some jellyfish. Chapter 17

11. Wireless Communication • Radio and television waves received by antenna • At broadcasting station, music and speech are converted from sound to electronic signals. • The electronic signals for AM broadcasts are then converted into a pattern of changes in the amplitude of a radio wave. Chapter 17

12. Sound signals are carried by varying either the amplitude (AM) or the frequency (FM) of radio waves pg. 555 • AM - long wavelengths easily reflected by ionosphere. • Can broadcast over long distances especially at night. • FM - frequencies much higher than AM. • Are not reflected by ionosphere. • Do not travel as far as AM. • Produce a better sound quality. Chapter 17

13. Cellular telephones - transmit and receive signals using high frequency radio waves or microwaves. • Wireless communication timeline pg.558 • 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) Chapter 17