1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Radiation from microwave ovens

  1. Nov 1, 2011 #1
    Everybody seems to agree that when a microwave oven is opened, no radiation escapes. On a different thread, somebody said: "Microwave radiation is like light: it absorbs quickly into objects after the source is turned off." This analogy to light is often used to explain why no microwave radiation escapes when the door is opened.
    But if I have understood correctly, the walls of the microwave oven almost completely reflect microwave radiation. So the equivalent thing would be would a light source within a room of mirrors. Where the light would of course not be instantly absorbed.
    Say that we had an empty oven and we open it, wouldn´t the radiation that had not been absorbed by walls and magnetron escape through the open door?
  2. jcsd
  3. Nov 1, 2011 #2

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    If you turn off a light bulb in a room full of mirrors and open the door a second later, do you still see the light?
  4. Nov 1, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    The radiation is absorbed in the realm of a tiny tiny fraction of a second. If you just hit the button to open the door while the microwave is running, the time it takes for the mechanism to actually open the door is long enough for any microwaves to be absorbed by the oven and food. Even empty the oven is not 100% reflective.
  5. Nov 1, 2011 #4


    Staff: Mentor

    What is "almost" here? Whatever it is, use that number and calculate how many times it has to reflect to fade into the background. Then, use the speed of light and the size of the microwave to figure out how long it would take. Is it possible to open the door that fast?
  6. Nov 1, 2011 #5


    User Avatar
    Gold Member

    Sure, but you are grossly underestimating
    1] just how fast light and microwaves move, and
    2] just how reflective any surface can be

    Even if the walls could reflect a thousand times, the radiation would all be dissipated in less than 3/100,000ths of a second.
  7. Nov 1, 2011 #6
    Google tells me that even if we assume a 0.5 m wide microwave, and 1 millisecond for time to open door, the microwaves will be reflected 599,585 times.


    Assuming 99.99% reflection that gives:
    .9999599585 = 9 x 10-25%

    Not a whole lot, even with very generous estimates.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook