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Help:Specific Heat and Electromagnetic radiation

  1. Mar 9, 2004 #1
    Please help uncloud my understanding

    #1.Why does the earth cool off much more quickly when the weather is clear than cloudy?
    My foggy understanding: The cloud cover “traps” the heat energy radiated from the earth because water has a high heat capacity, and so takes a longer time to heat up and pass on the heat energy by conduction to the rest of the atmosphere and space. It also reflects some of the energy absorbed back to the earth, which helps keep the earth warmer.

    #2. Why are lighter-colored clothes more comfortable than darker colored clothes in a hot climate?
    My foggy understanding: Darker-colored clothes absorb more wavelengths of electromagnetic energy than lighter colored clothes and thus, transform them into more infrared or heat energy, which is emitted to the wearer. This is the cause of their discomfort. Thus lighter colored clothes have a higher heat capacity than darker colors: it takes more energy to raise their temperature.
     
  2. jcsd
  3. Mar 9, 2004 #2

    russ_watters

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    Staff: Mentor

    Absorption/radiation have nothing to do with heat capacity. A white shirt reflects light and heat capacity has to do with absorbed heat.

    Simply put, a white shirt reflects energy instead of absorbing it and transferring it to you. A black shirt absorbs it, heating up the shirt, then you.

    Clouds block/reflect both visible and infrared radiation, making it harder for the ground to cool at night.
     
  4. Mar 10, 2004 #3
    Thanks Russ:smile:

    Now how does the heat capacity of the clothes relate to the energy emitted by the Sun?
    My foggy understanding: Lighter colored clothes have a higher heat capacity than darker colored clothes because it takes more energy radiation to raise the temperature of light colored clothes than for dark colored clothes of the same dimensions[mass, area etc]. More energy needs to be radiated to the lighter colored clothes because they reflect more energy per unit mass.

    Am I correct?
     
  5. Mar 10, 2004 #4
    heat capacity

    Not really,

    The heat capacity of an object has got to do with the energy it has to ABSORB to get a specific increase in temperature. So when an object reflects radiation very well, this doesn't say anything about its heat capacity...
     
  6. Mar 12, 2004 #5
    what ideas do you get when you think about cooling ?

    first thing that comes in my mind is the Evaporating system.

    evaporation is influenced by 4 things..

    Air movement, Temperature, * HUMIDITY *, Area exposed

    more humid it is, it would slow down the evaporation process.
     
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