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Unformatted text preview: 1 1 2 ) , ( / 5 2 = T k hc B e hc T I Lecture-26 Blackbody Radiation Wiens Displacement law relates wavelength at maximal emission to temperature as: Max Planck asserts: i) Emission spectrum from heated surface is same as that from cavity at same temperature; solid surface has emissivity <1 whereas cavity has =1. Cavity absorbs and re- radiates at own temperature; ii) Cavity emits photons at where h = 6.626 10-34 J s; iii) Plancks theory gives = hf P T = 2.90 10-3 m K 2 Physical Optics - Particle-like Effects Photoelectric Effect Experiment: i) Light incident on metallic surface ejects electrons if < min . ii) At given , photoelectrons have maximum kinetic energy, eV max = K max . iii) Photoelectron current scales with light intensity at given applied electric field. iv) Making use of Plancks theory, Einstein showed that K max is frequency dependent: , where W o is work function. Granularity in interference image field of light at low intensity suggests particle-like nature of light: Decreasing Light Intensity K max = hf - W o Sodium 3...
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