Waves? Chapter 17 Notes

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

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

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

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

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

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

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

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

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 Chapter 17

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? Chapter 17

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

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 Chapter 17

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 Chapter 17

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

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

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

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) Chapter 17