Electromagnetic Waves

• Wave is a temporary disturbance that transfer energy from one place to another
• two types of waves

  • mechanical waves
  • electromagnetic waves
• examples of mechanical waves

  • waves in water
  • sound waves in air
• Matter that mechanical waves are travelling through is called a medium
• electromagnetic waves do not need medium to propagate through, they travel through vacuum 
• electromagnetic waves are formed when electric field comes in contact with a magnetic field
• Electric field and magnetic field is measured at (right angle) perpendicular measurement to eachother
• EM waves travel at a constant of 3x10⁸m/s in vacuum
• Diffraction is bending of waves
• Interference will lower or higher the amplitude of the wave.
• EM waves are transverse waves
• Amplitude - Height of the wave, usually measured in meters
• the more amplitude, energy is carrying
• Crest - Highest point of a wave
• Trough - Lowest point of a wave
• Wavelength/Lambda - Distance between two crests/troughs
• Frequency - number of waves passing a point in a certain of time
• Time is equivalent to One Second
• Hertz (Hz) is used to measure frequency
• Hans Christian Oerested discovered that an electric current create a magnetic field in 1820
• Andre-Marie Ampere discovered Electrodynamics
• Micheal Faraday discovered Electromagnetic Induction in 1831
• Current is detected only when the magnet is moving in and out of the coil.
• James Clerk Maxwell discovered Electromagnetic in 1864
• Heinrich Hertz discovered radio waves-form of an EM wave
• EM waves travel in a speed of light and light is a form of EM wave
• In EM Spectrume, More wavelengths get smaller the higher frequency it gets
• Stream of mass-less particles is called Photons
• photons have certain amount of energy
• Radio waves have the longest wavelengths and the lowest frequency
• Radio waves are used to transmit sound and picture information over long distances
• 4 Characteristic of Radio Waves

  • Not line of sight
  • Can pass through walls
  • Longer range
  • Not light sensitive
• The whole region of the radio waves is divided into smaller regions or wavebands
• Low frequency waves aee suitable for communication over long distances
• To extend the range, a repeater is used
• Medium and high frequencies is used for broadcasting by local radio stations
• High frequencies called radio-frequency carriers can be modulated to match the electrical signal
• High frequencies can be reflected by the ionosphere
• Very high frequencies provide a higher quality broadcasting including stereo sound 
•  Amplitude modulation is the first successful method of audio transmission carried in the mid of 1870's