Waves all over, but harmful?

  1. The other day a friend of mine ask me if all the information sent through space by EM waves (TV, radio, cellphone, wireless internet) are any harmful to humans. My answer was that these are all radio waves which wavelengths are so large that they go around humans bodies. Also, the energy they carry is too low to do any damage in human bodies. How correct is this??
  2. jcsd
  3. LURCH

    LURCH 2,512
    Science Advisor

    As far as anyone has been able to determine, that EM radiation which is generated for sending information is harmless. Likewise the EM given off by powerlines and other man-made utilities. There are some who claim these sources of artificial EM do have harmfull side effects, but studies have so far produced no evidence to support that claim.
  4. SpaceTiger

    SpaceTiger 2,977
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, cell phones operate at wavelengths ~10 cm, so this isn't entirely correct, but it's certainly true that the waves' cross section for interaction with our bodies is much lower than for optical or infrared radiation. However, if the intensity of the radiation is high enough (or it operates at the frequency of a common molecular transition), it can still have a significant effect. Microwave ovens, for example, only operate at slightly higher frequencies than cell phones, and we know that they can heat large objects.

    I don't know the numbers, but I suspect the intensity of cell phone radiation is very small. I would be much more concerned about the danger they pose on the highway. :yuck:
  5. Galileo

    Galileo 2,002
    Science Advisor
    Homework Helper

    Humans are always exposed to radiation from natural sources like the sun. This can be dangerous as you know, if you the sunlight is intense you can get a nasty burn.
    Humans themselves radiate at wavelenghts of around 10 micron, which is shorter (and thus more energetic) then the radiation from cellphones, radio etc.
  6. There are no affects, but if the radiation is intense enough, it will heat things up just like in your microwave oven. Magnatrons, the devices inside that produce the microwaves can cause internal burns if you make a gun and activate it. Internal burns are not happy. :frown:
  7. I have a question: How does EM radation harm living tissue (when it does)?
  8. SGT

    SGT 0

    High frequency EM radiation: UV, X-rays, gamma radiation, have ionizing properties, so they can cause chemical reactions.
    In living tissue, chemical reactions can alter the molecules of DNA, causing mutations. In the gametes, those mutations can cause defective offspring. In other tissues, mutations can origin abnormal cell proliferation (cancer), that is why UV solar radiation can cause skin cancer and why X-ray professionals use lead shielding when scanning a patient.
    Microwaves have longer wavelengths and are not ionizing, so they are not a risk for cancer, but they can heat living tissue as Mk pointed. In the case of cell phones, their output power is in the order of 2.5 watts, much lower then the kilowatts of a microwave owen, so the scarelore about the dangers of cell phones seems to be exaggerated.
  9. But what EM waves go through objects? I mean light only goes through glass.
    How do the EM waves that being used transmitting information manage to go through matter (and human bodies)? And still keep the information.
    Last edited: Sep 13, 2005
  10. SGT

    SGT 0

    It depends very much of the dimensions and nature of the objects and the wavelength of the EM wave.
    Think of a series of huge ocean waves. A small boat will go up and down each wave without much disturbance. A huge ship will be hit simultaneously by two or more waves and be shaken.
    In a microwave oven, the wavelength is set to excite water molecules, warming the water contained in food, but the metal walls of the oven are opaque to the radiation. The grid in the door has holes that let light pass trough, allowing the vision of the food at the interior, but the dimension of the holes is calculated to block the EM waves.
    Germanium is opaque to visible light, but is transparent in a certain region of the IR spectrum, so lenses for applications in that region are made of Ge.
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