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E3A04

RADIO WAVE PROPAGATION · Electromagnetic Waves and Specialized Propagation: Earth-Moon-Earth (EME) communications; meteor scatter; microwave tropospheric and scatter propagation; auroral propagation; daily variation of ionospheric propagation; circular polarization

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In what direction does an electromagnetic wave travel?

  1. AIt depends on the phase angle of the magnetic field
  2. BIt travels parallel to the electric and magnetic fields
  3. CIt depends on the phase angle of the electric field
  4. DIt travels at a right angle to the electric and magnetic fields
Why An electromagnetic wave is transverse: the electric field and the magnetic field are at right angles to each other, and the direction of propagation is perpendicular to both of them. This is described by the Poynting vector, the cross product of E and H, which points along the direction energy flows. So if the E field is vertical and the H field is horizontal, the wave moves straight out at 90 degrees to both.
Watch out The idea that the wave travels parallel to the fields describes a longitudinal wave like sound, not an EM wave; radio waves have no field component along the direction of travel.
Think of your right hand: E, H and direction of travel are three mutually perpendicular axes, like the corner of a box.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of E3A

  1. E3A01 What is the approximate maximum separation measured along the surface of the Earth between two stations commu…
  2. E3A02 What characterizes libration fading of an EME signal?
  3. E3A03 When scheduling EME contacts, which of these conditions will generally result in the least path loss?
  4. E3A04 In what direction does an electromagnetic wave travel?
  5. E3A05 How are the component fields of an electromagnetic wave oriented?
  6. E3A06 What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
  7. E3A07 Atmospheric ducts capable of propagating microwave signals often form over what geographic feature?
  8. E3A08 When a meteor strikes the Earth's atmosphere, a linear ionized region is formed at what region of the ionosph…
  9. E3A09 Which of the following frequency ranges is most suited for meteor-scatter communications?
  10. E3A10 What determines the speed of electromagnetic waves through a medium?
  11. E3A11 What is a typical range for tropospheric duct propagation of microwave signals?
  12. E3A12 What is most likely to result in auroral propagation?
  13. E3A13 Which of these emission modes is best for auroral propagation?
  14. E3A14 What are circularly polarized electromagnetic waves?
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