1 LESSON_Q2

• Microwaves carry energy, and so with the other kinds of electromagnetic waves
• Electromagnetic waves


  Waves created as a result of vibrations between an electric field and magnetic field
• Electromagnetic waves


  • They transport energy
  • They transport momentum
  • They transport angular momentum
• In vacuum, electromagnetic waves travel at the same speed which depends on their frequency
• As frequency of an electromagnetic wave increases


  Its wavelength decreases
• Frequency


  The number of complete waves that pass by in one second
• Wavelength


  The distance between any two troughs or peaks
• Electromagnetic waves are propagated through the interaction of electric and magnetic fields
• The speed of electromagnetic waves in a vacuum is 3.00 x 10^8 m/s
• Compared to the speed of sound waves in air, the speed of radio waves in air is greater
• Oersted discovered the relationship between electricity and magnetism


  1820
• Ampere formulated the law of electromagnetism describing the magnetic force between two electrical currents
• Faraday discovered electromagnetic induction in 1831, generating an electrical current from a changing magnetic field
• Faraday's discovery of electromagnetic induction was a decisive milestone in the progress of science and society
• Ampere's Law


  Law that describes mathematically the magnetic force between two electrical currents
• Michael Faraday made his first discovery of electromagnetism


  1821
• Electromagnetic induction


  Electrical current generated from a changing magnetic field
• Joseph Henry's electromagnet


  • Insulated the wire instead of the iron core
  • Able to wrap a large number of turns of wire around the core and thus greatly increase the power of the magnet
• Self-induction


  Principle discovered by Joseph Henry
• James Clerk Maxwell


  • Proposed Faraday's electromagnetic induction to happen even in empty space
  • Added two basic principles of electromagnetism: (1) a changing electric field in space produces a magnetic field, (2) a changing magnetic field in space produces electric field
• Electromagnetic wave


  Form of moving energy proposed by Maxwell
• Maxwell concluded that the speed of electromagnetic waves must be 3 x 10^8 m/s
• Heinrich Hertz designed an experimental set up that was electrical in nature and able to generate and detect electromagnetic waves
• Electromagnetic (EM) waves


  • Disturbance that transfers energy through a field
  • Can travel through medium or empty space
  • Radiation is the term used to describe the transfer of energy in the form of EM wave
• EM waves can travel through vacuum at a constant speed of 300,000,000 meters per second (3.0 x 10^8 m/s)
• Crest


  Highest point of a wave, where the field is strongest
• Trough


  Lowest point of a wave, where the field is weakest
• Wavelength


  Distance between two identical points on successive waves
• Amplitude


  Measure of the energy a wave carries, determined by the distance from the midpoint to a crest or trough
• Frequency


  Number of wavelengths that pass by a point in a given time, expressed in Hertz (Hz)
• Electromagnetic wave


  • Combination of electric and magnetic fields
  • Electric field and magnetic field oscillate perpendicular to each other and to the direction of the propagating wave
• Speed of EM wave

  • 3 x 10^8 m/s, the speed of light (c)
  • Wavelength, frequency, and speed are related by the equation v = f
• Frequency


  1.5 x 107 Hz
• Wavelength


  5 x 10-7 m
• Calculating frequency of EM waves with given wavelength

  1. v=c=f

  2. f = c /

  3. f = 3 x 108 m/s / 5 x 10-7 m

  4. f = 6 x 1014 Hz
• Calculating wavelength of EM waves with given frequency


  1. v=c=f

  2. = c / f

  3. = 3 x 108 m/s / 610,000 Hz

  4. = 490 m
• Electromagnetic wave speed


  3 x 108 m/s
• Frequency


  1.5 x 1010 Hz
• Calculating wavelength from frequency and speed


  1. v=c=f

  2. = c / f

  3. = 3.0 x 108 m/s / 1.5 x 1010 Hz

  4. = 0.02 m
• Calculating wavelength from frequency


  1. v=c=f

  2. = c / f

  3. = 3.0 x 108 m/s / 4.80 x 1017 Hz

  4. = 6.25 x 10-10 m