Dismiss Notice
Join Physics Forums Today!

Help ! i need a explanation for this

  1. Jun 25, 2010 #1
    I got this from a book anyway

    An astronomer called William Herchel used some very accurate and sensitive mercury thermometer, he placed one in front of a spectrum of light and found that as he moved it across the bands of different colors from violet to red,the temperature rose.

    this what confuses me.....

    The equation for energy of the EM ray is E = hf which is Planks constant times the frequency, so that the energy is only depend on the frequency because the Planks constant is a constant..........X)but from the experiment above, it seems that the energy changes because of the wavelength...."the temperature changed when he moved the thermometer across the bands of different colors," does it mean that the energy also changes when the wavelength are not the same because when the temperature changes which also suggests that the energy has to change.... and the diffraction of light doesnt change the frequency but only the wavelength... If not..... where the .... is that spare energy comes from?

    please come up a explanation for this

    please do correct if any of my knowledge is not right....

  2. jcsd
  3. Jun 25, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Realize that frequency and wavelength of light are related by speed = frequency X wavelength. So light of different 'wavelength' is also light of different 'frequency'. It's two sides of the same coin.
  4. Jun 26, 2010 #3
    ooooh,,, thanks