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Simple Question: Unit of Light Oscillation

  1. Mar 22, 2012 #1
    I have a very simple question
    We all know that high frequency light has more energy than low frequency
    What IS oscillating, though?
    What are the units of the x and y axis?
  2. jcsd
  3. Mar 22, 2012 #2

    Vanadium 50

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    The electric and magnetic fields are what's oscillating.
  4. Mar 22, 2012 #3
    What are those measured in? Force?
  5. Mar 22, 2012 #4


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    Electric field has dimensions of force/charge. The units are N/C OR V/m

    Magnetic field has units of Teslas. You can look here to see how a Tesla is defined in terms of other SI units:

    http://en.wikipedia.org/wiki/Tesla_(unit [Broken])
    Last edited by a moderator: May 5, 2017
  6. Mar 23, 2012 #5


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    It might help if you first think of a very low frequency example of this. All EM waves share the same basic properties.
    Imagine an electromagnet (straight coil /'solenoid'), switched on. It will have a familiar 'field line' pattern around it like a bar magnet. You could go to a point in space, nearby and draw a line parallel to this field line with length proportional to the field strength (a vector). Now swap the connections. The change will take some time to reach your measuring point but then the field vector will have changed direction. Keep alternating the connections (better still, make the alternations sinusoidal in time) and the (slightly delayed) vectors will vary sinusoidally. It so happens that your coil will also be producing a varying Electric field at your measurement point and this E vector will be at right angles to the H vector. This variation takes the form of a wave, propagating outwards, with the E and H fields at right angles to the direction of propagation.

    With light, the same thing is happening - just faster. There is an extra complication for most sources of light and that is the light is produced by many non-coherent sources (atoms and molecules) so the wave at a point in space is a jumble of many different waves at slightly different frequencies but you can treat it, for many purposes (reflection at a surface, for instance) as if it were just one wave, as with a Radio wave. From a Laser, the waves are all 'in step' and we have a coherent beam - just like from a radio transmitter.

    Each atom will release a specified amount of energy in the light it produces (a Quantum or Photon). As you say, the energy of each photon is proportional to the frequency. The Field vectors, however, are macroscopic quantities so they will be proportional to the total amount of light.
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