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!

Infra-red Electromagnetic waves.

  1. Jul 16, 2009 #1
    I understand that they come from objects with high temperature. But to me it makes no sense because from what I understand temperature is measuring the small molecules moving around, I do not see where the relationship is between the two. Do I have an idea mixed up?
  2. jcsd
  3. Jul 16, 2009 #2
    The small molecules moving around give off energy in the form of infra red photons. This means they have less energy, so move around less, so the temperature of the object drops.
  4. Jul 16, 2009 #3
    It's one of the three forms of heat transfer, radiation. All matter with heat gradually emits radiation and cools (unless it absorbs more than it emits). The greater the temperature the more radiation and higher the frequency. Infrared light is no more related to heat than any other type of light (radio, visible, x-ray, gamma). It just so happens that objects with temperatures we would normally call hot have their emission peak in infrared.

  5. Jul 16, 2009 #4
    elctromagnetic waves are transverse in nature. not affected by electric and magnetic field.
  6. Jul 19, 2009 #5
    Is there a reason why the objects with "hot" temperatures have there emission peak in the infrared? Does the emission peak depend mostly on the chemical composition or physical nature of the object? If all light is heat, is there a difference between absorption and emission of light and heat transfer, or are they synonymous? Don't different frequencies of light affect matter in different ways (affecting different electron energy levels and the nucleus of atoms, molecular torsion, reflecting off, scattering off) instead of just causing them to heat up (random motion) regardless of frequency? Do all of these interactions of matter with light occur at the quantum level? I'm confused on how all light causes heating , but the effects on matter can be so drastically different.

    Thank you
  7. Jul 19, 2009 #6
    The radiation comes not from the motion of the particles, but rather their colissions with each other. In a warmer object, the colissions are of higher energy, allowing higher energy photons to be produced. This is what moves the peak to shorter wavelength radiation as temperature increases.
  8. Jul 19, 2009 #7
    see Blackbody radiation. I wouldn't say "hot" objects emit in the infrared that's pretty low energy. Things that are about room temperature emit in the infrared, you get hotter like a lightbulb and you get yellow, you get even hotter like certain types of blow torches, you get way hotter like the surface of a star and you get UV-cosmic depending on the layer.
  9. Jul 19, 2009 #8
    Is the collision between two atoms mediated by a photon? Or else, it would seem that there would be a discrepancy between heating by collisions between atoms and heating by absorption of photons by atoms. Is all heat related to the em force?

    Thank you for your responses
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook