EM Waves

• Electromagnetic waves


  Electric and magnetic fields traveling through empty space with the speed of light
• Propagation of Electromagnetic Wave

  1. Accelerating charges produce changing electric and magnetic fields

  2. Changing electric fields produce magnetic fields

  3. Changing magnetic fields produce electric fields

  4. This interplay between induced electric and magnetic fields leads to propagating electromagnetic waves

  5. Electromagnetic waves can propagate through free space
• Wave equation


  Relates speed of propagation (v), frequency (f) and wavelength (Λ)
• In a vacuum or air, all electromagnetic waves travel at a common speed equal to 3 x 10^8 m/s
• Photon


  The smallest (quantum) unit of light/electromagnetic energy<|>Photons are generally regarded as particles with zero mass and no electric charge
• Wave-particle duality


  The amount of energy a photon has can cause it to behave more like a wave, or more like a particle
• EM waves

  • Transverse waves
• Amplitude (A)


  The height of a wave, usually measured in meters (m)<|>The greater the amplitude (A) of a wave the more energy it carries
• Wavelength (λ)


  The distance between two consecutive crest or trough, usually measured in meters
• Frequency (f)


  The number of waves passing a point in a certain time, measured in hertz (Hz)
• Speed of light (c)

  All electromagnetic waves travel at the same speed of about 3.00 x 10^8 m/s through a vacuum
• Wave Equation

  v = f λ
• Electromagnetic spectrum

  Continuous range of electromagnetic waves arranged in order of frequency or wavelength<|>Divided into regions on the basis of a certain frequency or wavelength interval
• Radio waves

  Longest wavelengths in the electromagnetic spectrum, ranging from 10^-1 m to 10^4 m<|>Frequency range from 30 kHz to 3000 MHz
• Types of radio waves

  • Low frequency (30-300 kHz)
  • Medium frequency (300-3000 kHz)
  • High frequency (3-30 MHz)
  • Very high frequency (30-300 MHz)
  • Ultra high frequency (300-3000 MHz)
• Applications of radio waves

  • Long distance communication and navigation
  • AM radio broadcasting
  • Shortwave broadcasting
  • FM radio broadcasting
  • Police radio communication
  • Military aircraft and television transmission
  • Modern mobile phones and global positioning systems
  • Radar
  • Wi-Fi, Bluetooth, GPS and RFID
• Microwaves


  Portion of the electromagnetic spectrum at the higher frequency end of the radio spectrum<|>Frequency range from 300 MHz to 300 GHz, wavelength from 10^-3 m to 10^-1 m
• Microwaves


  A portion or "band" found at the higher frequency end of the radio spectrum, but they are commonly distinguished from radio waves because of the technologies used to access them
• Microwaves

  • The microwave region in the EM spectrum lies somewhere from 300 MHz to 300 GHz , with wavelength corresponding to 10−3 m to 10−1 m
  • James Clerk Maxwell is credited for discovering microwaves in 1864
• Microwaves


  Cause water and fat molecules to vibrate, which makes the substances hot
• Radar

  Works by sending out bursts of microwaves, detecting the "echoes" coming back from the objects they hit, and using the time it takes for the echoes to come back to work out how far away the object is
• Infrared

  Infrared radiations (IR) have a lower frequency than the red part of the visible light, with frequencies ranging from 3x 10 to 4x10^14 Hz and wavelengths ranging from 7.5x 10−7 m to 10−3 m
• In 1800, William Herschel conducted an experiment measuring the difference in temperature between the colors in the visible spectrum and discovered infrared light
• Uses of infrared

  • Remote controls for TVs and video recorders
  • Physiotherapy heat lamps
  • Short-range communications
  • CCD chips in digital cameras
  • Burglar alarm systems
  • Thermal imaging cameras
  • Weather forecasting
• Visible light


  The segment of the electromagnetic spectrum that the human eye can view, with wavelengths from 4x 10−7 m to 8x 10−7 m
• Visible light spectrum


  The sequence of colors from longest to shortest wavelength: red, orange, yellow, green, blue, indigo, violet (ROYGBIV)
• Uses of lasers


  • Compact Disc & DVD players
  • Laser printers
  • Aircraft weapon aiming systems
• Ultraviolet (UV) light


  Has shorter wavelengths than visible light, with UV-C being the most harmful and UV-A being used for treating skin conditions
• Uses of UV light

  • Getting a sun tan
  • Detecting forged bank notes
  • Sterilizing surgical equipment and air
  • Sterilizing food and drugs
  • Treating vitamin D deficiency and skin disorders
• 1. rays

  Have much higher energy and much shorter wavelengths than ultraviolet light, between 0.03 and 3 nanometers
• Uses of X-rays

  • Medical imaging
  • Airport security checks
  • Astronomy
• Gamma rays


  Have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum, produced by the hottest and most energetic objects in the universe
• Uses of gamma rays

  • Radiotherapy to kill cancer cells
  • Sterilizing food and medical equipment