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How higher frequency EM waves become more dangerous

  1. Dec 21, 2014 #1
    How high frequency makes waves dangerous for us.also does all em waves have same speed of light?
     
  2. jcsd
  3. Dec 21, 2014 #2
    Energy of the wave is proportional to its' frequency. Higher the energy, more damage possible. In vacuum all EM waves have same speed (speed of light).
     
  4. Dec 21, 2014 #3

    sophiecentaur

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    Once the energy of the (individual) photons becomes high enough to cause ionisation, they become much more damaging to living cells (and electronics, too). The problem starts with UV and extends right up into gamma radiation.
     
  5. Dec 21, 2014 #4

    Drakkith

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    To bounce off of what Sophie said, EM waves have their energy divided into "quanta", little packets of energy that they interact with matter through. The higher the frequency, the larger this packet of energy is. Once the frequency of the wave becomes high enough, about the UV range and higher, each packet contains enough energy to knock electrons completely out of their atom and molecules. Removing an electron is called ionization and leaves behind two highly reactive particles, the electron and the atom/molecule, which can then react with other atoms/molecules in your body to cause damage.
     
    Last edited: Dec 21, 2014
  6. Dec 21, 2014 #5

    sophiecentaur

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    100% approval, there.
    Notice that he never, once, mentioned the word Particle. Something we could all make sure to include in our New Year's Resolutions.:)
     
  7. Dec 21, 2014 #6
    Sophie Sir 99.9% approval must be there to what Drakkith Sir has said.As you will carefully notice post there is "eat packet".Well I have read in books that E=hv but can anyone explain proof or give experiment link for formula verification.Also how does speed of em waves change when not in vacuum?
     
  8. Dec 21, 2014 #7

    Drakkith

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    http://en.wikipedia.org/wiki/Planck–Einstein_relation
    http://www.franklychemistry.co.uk/20to9/snap_tuition/y13/Energy_of_photon.pdf
    http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html#c3
    http://disciplinas.stoa.usp.br/pluginfile.php/48089/course/section/16461/qsp_chapter10-plank.pdf

    Experimental verification:
    http://en.wikipedia.org/wiki/Photoelectric_effect
    Every CCD and CMOS camera sensor ever made depends on the energy of an EM wave being quantized.
     
  9. Dec 21, 2014 #8

    sophiecentaur

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    The Einstein work was the early stuff that clinched a lot of the Quantum ideas. It seemed to appeal to everyone who I taught it too - even when they didn't see how simple and elegant it is.
     
  10. Dec 21, 2014 #9

    sophiecentaur

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    @Drakkith Bad boy, naughty boy. Your spelling is all to hell! :-p
     
  11. Dec 21, 2014 #10
    Thanks Drakkith sir for providing me with proof and experiment link although I am not so acquainted with all those partial derivatives and proof stuff and it all looks hi-fi at the moment.Will look in future to all these by gathering enough basic information.
    Can anyone answer my second question that how EM waves speed changes when not in vacuum,that is not speed of light?
     
  12. Dec 21, 2014 #11

    sophiecentaur

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    As you don't want a Maths based answer, ( and I can't blame you at this stage!) I could suggest that you look at it this way. As an EM wave propagates through a substance that is an insulator (metals are not included in this simple example), the Fields in the EM wave will have an effect on the charged particles in the material. This will be the electrons for all but the highest frequency waves. You could imagine the electrons moving slightly, 'in synchronism with the fields in the wave. As they move, they will re radiate a wave at the same frequency as the incident wave but there will be a delay. So that will have the effect of increasing the time taken for the energy to get through the substance i.e. the speed of the wave.
    The amount that the wave is slowed down will depend upon the number of electrons it encounters on the way through so you would expect the more dense substances to slow the waves more than the less dense. Air makes very little difference at all but water and glass will have a very significant effect on the speed.
    Many (most) dense substances will tend to absorb the energy as it passes through so they tend not to be 'transparent'.
     
  13. Dec 21, 2014 #12

    Drakkith

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    Fixed!
     
  14. Dec 22, 2014 #13
    It looks like both you Sophie Sir(though your boat name is Sophie) and Drakkith Sir have deep knowledge in this subject.I got it all by explaining in simple manner.
     
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