Electromagnetic waves

• Electromagnetic waves


  Waves made by vibrating electric charges that can travel through space where there is no matter

  
• How electromagnetic waves are formed

  1. Vibrating electric charges produce changing electric and magnetic fields

  2. These changing fields create each other and propagate as a transverse wave

  
• Electromagnetic waves do not need matter to transfer energy
• Changing magnetic field


  Creates a changing electric field
• Making electromagnetic waves


  1. Vibrating electric charge changes electric field

  2. Changing electric field creates changing magnetic field

  3. Cycle repeats, creating propagating wave

  
• Electromagnetic waves


  • Transverse waves with vibrating electric and magnetic fields at right angles to direction of travel

  
• All matter contains charged particles that are always moving, therefore all objects emit electromagnetic waves

  
• Wavelength becomes shorter as temperature of material increases
• Electromagnetic waves carry radiant energy

  
• Speed of electromagnetic waves


  300,000 km/s in space (speed of light)

  
• Electromagnetic waves usually travel slowest in solids and fastest in gases
• Wavelength


  Distance from crest to crest (or trough to trough)

  
• Frequency


  Number of wavelengths that pass a given point in 1 second
• As frequency increases


  Wavelength becomes smaller
• Photon


  Particle that electromagnetic waves can behave as, with energy dependent on frequency

  
• Electrons fired at two slits form an interference pattern similar to waves

  
• Young's experiment showed the wave-like nature of light

  
• Electromagnetic spectrum


  • Very long wave radio
  • Long, medium and short wave radio
  • FM radio, television and radar
  • Infrared (heat) radiation
  • Visible light
  • Ultraviolet light
  • X rays
  • Gamma rays

  
• Microwaves


  Radio waves with wavelengths less than 30 cm and higher frequency
• Radar


  Radio Detecting And Ranging, used to find position and speed of objects by bouncing radio waves off them
• Magnetic resonance imaging (MRI)


  Uses radio waves and a strong magnet to create images of the body's tissues
• Infrared waves


  Electromagnetic waves with wavelengths between 1mm and 750 billionths of a meter

  
• Visible light


  Range of electromagnetic waves humans can see, from 750 billionths to 100 billionths of a meter

  
• Ultraviolet radiation can be useful for making vitamin D, sterilizing equipment, and detecting fingerprints
• Ozone layer


  Layer 20-50 km above Earth that absorbs harmful UV rays from the Sun
• Destruction of the ozone layer could be harmful to humans and other life on Earth
• 1. rays and gamma rays

  Electromagnetic waves with the shortest wavelengths and highest frequencies, able to penetrate skin and muscle
• High exposure to X-rays and gamma rays can cause cancer
• Radio transmission


  1. Sound waves converted to electronic signal

  2. Electronic signal used to modulate carrier wave

  3. Carrier wave transmitted as electromagnetic waves

  4. Receiver converts electromagnetic waves back to electronic signal

  5. Electronic signal converted back to sound waves
• Carrier wave


  Frequency of the electromagnetic wave used by a radio station
• AM radio


  Amplitude of carrier wave is modulated, but frequency is constant
• FM radio


  Frequency of carrier wave is modulated, but amplitude is constant
• Cathode-ray tube


  Vacuum tube in which beams of electrons are produced to display images on a screen
• Telephone communication


  1. Sound waves converted to electronic signal

  2. Electronic signal transmitted as radio waves

  3. Radio waves received and converted back to electronic signal

  4. Electronic signal converted back to sound waves
• Cordless phones


  Transceivers that transmit and receive radio signals at different frequencies to allow two-way communication
• Pagers


  Radio receivers that receive electronic signals transmitted as radio waves and display messages
• Communications satellites


  Satellites that receive microwave signals, amplify them, and retransmit them to different locations on Earth
• Global Positioning System (GPS)


  System of satellites, ground stations, and receivers that determines location by measuring the time it takes for radio waves to travel from multiple satellites