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Homework Help: Need help with electromagnetic waves

  1. Mar 13, 2005 #1
    Let us model the electromagnetic wave in a microwave oven as a plane traveling wave moving to the left, with an intensity of 26.6 kW/m^2. An oven contains two cubical containers of small mass, each full of water. One has an edge length of 6.40 cm and the other, 12.8 cm. Energy falls perpendicularly on one face of each container. The water in the smaller container absorbs 70.0% of the energy that falls on it. The water in the larger container absorbs 91.0%. (That is, the fraction 0.3 of the incoming microwave energy passes through a 6.40-cm thickness of water, and the fraction (0.3)(0.3) = 0.09 passes through a 12.8-cm thickness.) Find the temperature change of the water in each container over a time interval of 510 s. Assume that a negligible amount of energy leaves either container by heat.

    How does temperature tie in with this? I can't find any formula with intensity that deals with temperature. Any help would be great! Thanks in advance! :)
  2. jcsd
  3. Mar 13, 2005 #2
    You're going to need a little bit of chemistry here.

    [tex] \Delta E = m c \Delta T [/tex]

    where [tex] \Delta E[/tex] is change in energy, and [tex] m, \ c, \ \Delta T [/tex] are mass, specific heat capacity, and change in temperature, respectively.

    Can you relate [tex]I[/tex] to [tex] \Delta E[/tex]?
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