Energy Talk!

srinivasarao k asked:


In Physics, Interference of light is in accordance with the principle of conservation of energy. But, in some text i found that diffraction doesn’t obey, even though both are wave phenomenon. If it is so, what is the reason behind it.

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4 Responses to “Explain, whether diffraction of light obeys principle of conservation of energy ? How ?”

1. Elana Says:
   November 13th, 2007 at 9:12 pm

   Clearly it MUST obey conservation.

   Beware, however, that when you defract light with matter, you remove energy in the form of heat.

2. Kes Says:
   November 15th, 2007 at 10:48 pm

   Ignoring light that is absorbed rather than diffracted, the light energy entering the diffracting media (glass?) must be the same as the light energy exiting the media if the wavelength of the light (photons) is unchanged. Light (photons) travel as mass-less packets of energy at the speed of light (which is constant). The amount of energy carried by the photons determine their wavelength (and color).

3. mathematician Says:
   November 16th, 2007 at 11:32 pm

   In general, a lot of care must be taken when working with the energy of wave phenomena. It is very difficult to localize energy within distances less than one wavelength.

   In diffraction, light is interacting with matter, so some will be absorbed by that matter and be converted into heat. Furthermore, the matter will re-radiate, so it is actaully a subtle thing to determine where the energy goes. In fact, technically speaking, it is the re-radiation by the matter that creates the diffraction pattern by cancelling the portion of the wave that would have gone through the matter.

   In any case, the energy discrepancy will show up as heat in the matter.

4. Pearlsawme Says:
   November 18th, 2007 at 5:10 am

   In explaining interference of light we dont need ‘ half period zones’

   But diffraction is well explained with the help of half period zones which is based only upon conservation of energy principle.

   Hence if at all a doubt arises about the obeyance of conservation of energy priciple, it should be with interferece rather than with diffraction.

   However both agrees well with the conservtion of energy.

   InPhysics, one cannot accept any theory which is not based on coservation of energy. A theory is accepted if and only if it obeys conservation of energy.