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Making Light

  1. Jun 24, 2008 #1
    Here's a pondering I have had for a while;

    suppose we created and alternating electric field of a certain frequency f,
    and then we created an alternating magnetic field to occur perpendicularly to the electric field, pi (or whatever) out of phase with electric field, also with a frequency f,

    would we see light of color f?
  2. jcsd
  3. Jun 24, 2008 #2


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    Staff: Mentor

    I'm not sure how that would be possible - red light is at about 400 teraherz. Computer chips have run into a brick wall below 10 gigaherz and are limited by heat and physical size (electrons just can't be made to oscillate that fast in an electrical circuit).

    However, radio waves are the same animal as light (electromagnetic radiation), but of much lower frequency and are made with oscillating electromagnetic fields.
  4. Jun 24, 2008 #3
    To me, yes it would be,bcoz what the basic definition of electromagnetic radiation says regarding component of electromagnetic radiation is followed by your pondered experiment.
    It was really a fabulous question and practically speaking answer to this question is not so easy to respond,
    because then we have to talk of ideal synchronisation of two components.
  5. Jun 24, 2008 #4
    Actually, our eyes don't respond to the magnetic field so the question is would we "see" an alternating em wave as light.

    Yes, if it was within the visible spectrum.
  6. Jun 24, 2008 #5
    If our eye's don't respond to the magnetic component (I understand it exerts a relatively neglible force on an electron compared to the E-Field), why can't we see alterneting electric fields,

    for example, if we we're switching a capcitor to opposing polarities very fast (terahertz, may not be achievable with current electronics), would we 'see' light?
  7. Jun 24, 2008 #6


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    It is IMPOSSIBLE to generate a changing electric field WITHOUT a changing magnetic field. Just ask Maxwell.
  8. Jun 24, 2008 #7
    First: You have to take into consideration that an oscillating electric field creates a magnetic field in space and vice versa that is , EM waves can propagate keeping their energy because they are intrinsic ,so the electric field generates the magnetic field and mutually , The magnetic field regenerates the electric field , Thus , Propagation is stable on the stability of the medium

    Second:even if we reached this frequency what we would see is the EM wave generated due to vibration. EM fields themselves vary in intensity with distance so what you'll get is a "chaos of electrons" in your sense nerves.

    third: the frequency of EM waves is a characteristic that determines it's energy and energy gives information about the size of the photon that enters the iris (yes , you must take quantum effect into consideration ) your vision cells have a definite resolution according to their size.

    At last I expect you're going to have a white glow in your eyes then, Complete darkness!!!
  9. Jun 24, 2008 #8
    Very interesting, thank you for the insights.

    So we can't make a changing electric field without inducing a corresponding magnetic field (which has a few practical uses I believe), but say we just switched something on, a giant capacitor for example, will there be a corresponding magnetic field while the electric field is changing?

    If so, by essence, you cannot "create" an electric field without inducing some kind of magnetic field in its vicinity, unless the field exists at t=0 in which case their is no CHANGE in the electric field so no magnetic field follows.

    A bit of chicken and egg scenario I guess.
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