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Very basic questions regarding thermal energy and radiation.

  1. May 9, 2012 #1
    So we were studying about different types of heat transfers, conduction, convection, and finally we learned about radiation, it was sort of confusing, so im going to write stuff, and hopefully someone can see what i wrote and see if its correct.


    basically the book says

    'Radiation

    Energy from the sun is transferred through the vacuum of space, without being carried by particles, in the form of radiation. In cases like this, hot objects lose thermal energy by emitting electromagnetic waves. Sometimes these electromagnetic waves are visible and the objects glow brightly like the sun or like very hot metal. At other times warm objects emit non visible forms of electromagnetic radiation, such as microwaves, infrared waves and x rays. Usually hot objects lose heat due to infrared rays. This process is sometimes called heat radiation. '


    and what i got from that is

    -Light is a form of electromagnetic wave

    -not all forms of electromagnetic waves are visible

    -All electromagnetic waves are radiation?

    - Thermal energy is transferred from heat to radiant energy(or radiation)
     
  2. jcsd
  3. May 9, 2012 #2

    cepheid

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    Staff Emeritus
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    Yes.

    Yes.

    Note: some people use the term "light" to refer only to the visible portion of the electromagnetic spectrum, but you will also see people using light as a more general term that could encompass radiation from any part of the spectrum: e.g. ultraviolet "light", infrared "light", x-ray "light". Or even just, "it emits 'light' " (not necessarily implied to be visible). So, this second sense of the word "light" can be thought of as a direct synonym for electromagnetic radiation. I just thought I'd point this out, since the terminology can be confusing.

    Yes.

    Radiation is the more general term for something that radiates: i.e. that moves outwards in all directions from one central source. Actually, it doesn't necessarily have to be in all directions. Anyway, electromagnetic radiation is a type of radiation, but the word radiation can be used in other contexts to refer to different things. For instance, the radiation associated with "radioactivity" consists of high energy particles (typically atomic nuclei) that are emitted as products of the radioactive decay of unstable elements. That is not the type of radiation we are talking about here, but it is the thing that is most commonly thought of as "radiation" by the lay person.

    Yes.

    When we talk about about "radiation" as a mechanism of heat transfer, we are talking specifically about electromagnetic radiation. Things can cool down (lose thermal energy) by radiating light (electromagnetic radiation), and this is the heat transfer mechanism that is being referred to as "radiation" in your book (in contrast with conduction and convection, which are cooling mechanisms that don't involve emitting light).
     
    Last edited: May 9, 2012
  4. May 10, 2012 #3
    I see...so i also read that when electrons jump down an orbit, they release photons(light) would that be considered radiation? Is that nuclear radiation or electromagnetic radiation thats being referred to in my book?

    #edit. that energy that is released as light(Photons) is the exact difference that exists between the 2 levels of energy difference of the orbits, right?
     
    Last edited: May 10, 2012
  5. May 10, 2012 #4
    Yes, that would be considered radiation.

    No, Nuclear Radiation tends to be Helium nuclei, high energy electrons, or high energy light, not just necessarily light.

    And yes, but don't forget the uncertainty in energy proposed by QM.
     
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