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Ultraviolet catastrophe
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Ultraviolet catastrophe



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  • 1. ULTRAVIOLET CATASTROPHEOverview Called Rayleigh-Jeans Catastrophe Late 19th century classical physics prediction that an ideal black body at thermal equilibrium will emit radiation with infinite powerWhat is a Blackbody? Idealized physical body- absorbs all incident radiation to it This makes it a perfect radiator too. These radiation depends on the temperature of the object ↑Temp (T) = ↓wavelengths (from invisible infrared to visible fire to UV rays)Classical Electromagnetism Thermal radiation is due to accelerated atomic particles near the object’s surface. Higher temperature = more excited “oscillators” = higher frequency and more energy Equipartition Theorem = the excited particles share the same acceleration/energy and it can be in quantized valuesRayleigh-Jeans LawWhere:U = radiation intensityKB = Boltzmann’s constantT = Temperatureλ = wavelengthThe Problem: Agreeable for short wavelengths but as lambda decreases (i.e. UV rays) intensity/energy/power approaches positive infinity BUT experiments share that the limit of energy as wavelength approaches 0 is 0. Also, experiments show that power per unit area always remains finite! Thus the UV catastrophe—although there are other high frequency waves. I.e. – according to Rayleigh Jeans Law, heating something with weak UV light vs. high intensity microwaves, the UV light will heat something greater, despite its weakness
  • 2. Very false, but should the UV catastrophe hasn’t been disproved, it will still be believed true.The Solution: Max Planck’s Theory VS. Rayleigh-Jeans LawPlanck’s Theory He proposed that to reduce the intensity of high frequency waves, the high frequency oscillations of atoms should be limited (which would match the experimental results) This put a limit to the energy if high frequency waves Where h= 6.63 x 10-34 J∙s →Planck’s ConstantTwo Assumptions Planck ignored Equipartition Theorem and suggested that: o E= hf→ Energy is quantized in multiples of h Molecules emit or absorb energy in discrete packets by jumping from one quantum state to anotherConsequences: Planck’s solution to the ultraviolet catastrophe is considered the starting point ofquantum physics =. Five years later, Einstein would build on this quantum theory to explain thephotoelectric effect, by introducing his photon theory. While Planck introduced the idea ofquanta to fix problems in one specific experiment, Einstein went further to define it as afundamental property of the electromagnetic field.References: http://spiff.rit.edu/classes/phys314/lectures/planck/planck.html Serway, Beichner(2000). Physics for Scientists and Engineers. Harcourt College Publishers: Orlando, Florida