3 LESSON_Q2

• Practical Applications of Electromagnetic (EM) Waves
• Electromagnetic (EM) waves


  A disturbance that transfers energy through a field, can travel through medium or empty space
• Regions of the EM spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Radio communication


  1. Electrons vibrate in antenna

  2. Radio waves produced

  3. Transmitted over long distances

  4. Received by antenna

  5. Converted back to original form
• Radio waves


  • Longest wavelength in EM spectrum
  • Used to transmit sound and picture information over long distances
• Low frequency radio waves


  • Suitable for communication over great distances
  • Range limited by earth's curvature
  • Repeater used to extend range
• High frequency radio waves

  • Can be reflected by ionosphere
  • Enables transmission over great distances
• Medium and high frequency radio waves


  • Used for local radio station broadcasting
• Radio station broadcasting


  1. Sound converted to audio-frequency (AF) signals

  2. AF signals used to modulate radio-frequency (RF) carrier waves

  3. Amplitude modulation (AM) used in standard broadcasting

  4. Frequency modulation (FM) used for higher quality broadcasting
• Radio waves


  • Whole region divided into wavebands
  • Each waveband allocated to specific radio service
• Microwaves


  • Shorter wavelength than radio waves
  • Used in satellite communications, radar, TV transmission, cooking
• Satellite communication


  1. Microwaves penetrate atmosphere and ionosphere

  2. Transmitted to satellite

  3. Satellite amplifies and re-transmits signal to receiving antenna on Earth
• Communication satellites


  • Travel at 35,000 km altitude, 11,300 km/h speed
  • Revolve around Earth at same rate as Earth's rotation, appear stationary from Earth
• Most communication satellites used for telephone services, rest for TV transmission
• Microwaves


  High frequency waves that can penetrate the atmosphere of the earth and into the ionosphere and to space
• Satellite communications


  1. Microwaves transmitted to satellite

  2. Satellite amplifies and re-transmits signal

  3. Signal received by antenna on Earth
• Communication satellites


  • Travel around the earth at an altitude of 35,000 km above the equator
  • Move at a speed of 11,300 km/h
  • Revolve around the earth every 24 hours, the same rate as the rotation of the earth
  • Appear stationary when seen on Earth
• Radar


  Radio Detection and Ranging system that uses microwaves reflected by small objects to detect and locate them
• How radar works


  1. Antenna whirls around continuously to scan area

  2. Transmitter sends out narrow beam of microwaves in short pulses

  3. Distant object reflects some of the signal back to receiver

  4. Direction and distance of object calculated from transmitted and reflected pulses
• CATV (Cable TV)


  Uses microwaves to transmit television news coverage from mobile broadcast vehicles back to the station
• Cell phones


  Radio transmitters and receivers that use microwaves
• Microwave oven


  Foods absorb certain microwave frequencies strongly, agitating water molecules and creating heat to cook the food
• Infrared waves


  Electromagnetic radiation in the lower-middle range of frequencies, beyond the red end of the visible light spectrum
• Infrared waves


  • Longer wavelength infrared waves produce heat, shorter wavelength infrared rays do not produce much heat
  • Amount and wavelength of infrared radiation depend on temperature
• Applications of infrared waves

  • Infrared photographs from satellites provide details of vegetation
  • Infrared temperature scanners for medical diagnosis
  • Infrared remote controls for TVs, video, and other electronics
  • Infrared cameras with transmitters that send out infrared pulses
  • Night-vision goggles that use IR
• EM wave applications


  • Radio waves: Radio and television communication
  • Microwaves: Satellite television and communication, Cooking
  • Infrared waves: Remote control, Household electrical appliances