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!

Homework Help: Metal in Microwaves

  1. Apr 21, 2008 #1
    A compact disc contains an extremely thin sheet of aluminum. If you put a larger block of metal in a microwave oven along with a CD and turn the oven on,

    a) nothing significant happens
    b) only the metal will spark and then melt
    c) the metal will melt and the CD will spark
    d) only the CD becomes hot enough to soften and sparks dance about its surface

    I know that when you put a CD in a microwave D is what happens. I also know that if you put a large block of metal in the microwave nothing significant happens because thick metal conducts electricity well. But when you combine these two objects does anything different happen? My intuition is to go with D, since I don't think that the metal block would interfere with the microwaves that would cause the aluminum on the CD to spark, but I'm not entirely sure.

    One more quick question...if metal bowls would help reflect microwaves through the food, why are most microwave safe bowls glass (i.e. Pyrex)? Is it better to cook foods in metal bowls or glass bowls?
  2. jcsd
  3. Apr 21, 2008 #2
    I'm pretty sure the answer is D - like you said.
    But the important thing to note is that even though nothing significant happens visually, in a short period of time with a large piece of metal --> important things are happening.
    You should never use metal in the microwave. Small metal, as you know, will spark, burn melt, etc. large metal is bad because it reflects microwaves (again like you said), but thats bad - because it will damage the microwave, and increases the flux out of the microwave (although it still won't be very much). No shielding in a microwave oven is perfect; it works best when waves are being absorbed by something inside - like food. Thats why glass etc is good, because its transparent to microwave radiation - allowing it all to be absorbed in what you're heating.
    (have you tried crumpled aluminum-foil?)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook