Classical Physics failure?

Question

Can any one say what Rayleigh Jeans law esp. its failure given that it can be excited even at room temperatures (dat stuff)... i need easy to understand answers wid d standards of d first year Engg. student. Also say how quantum mechanics hailed?

Answer 1

Rayleigh-Jeans law says energy radiated from a blackbody goes like one over the wavelength of light to the 4th power.  Since a blackbody emits over the entire spectrum, Rayleigh-Jeans predicts that the blackbody radiates an infinite amount of energy since as wavelength gets smaller, the energy associated with it increase drastically.  This is just not physically possible.  The law fails to describe teh observed spectrum of a blakbody at short wavelengths - the spectrum reachs a maximum value at some wavelength (which depends on the temperature of the blackbody) and then decreases to zero as the wavelength gets shorter.  

I'm not sure what you are asking about quantum mechanics.  However, Planck fromulated a correct explanaition for teh blackbody spectrum but to do it he had to accept the idea that light came in discrete packets, which we now call photons, and that the energy of any packet is given by a constant, h, times the frequency of the light (h is now called Planck's constant).  This was the start of quantum theory since now light was treated as discrete particles with qunatized energy - i.e. you can't have less than a photon of light energy at any given optical frequency.