2Electromagnetic Radiation (cont’d)EM radiation is NOT associated with the movement of matter. It is only a periodic change in the electric and magnetic fields.Electromagnetic Radiation (cont’d)All EM radiation travels at the same speed (in a vacuum), the speed of light (c) c = 3.00 x 108m/sFrequency and wavelength are inversely proportional, i.e. ν ∝1/λvia c ∴Electromagnetic Radiation (cont’d)There are many forms of EM radiation, differing only in frequency (or wavelength or energy) and how they are produced or detected (also see Table 6.1)
3Quantized Energy and PhotonsThe development of electronic structure of atoms depended on 3 experiments which had to be explained:1) blackbody radiation2) the photoelectric effect3) emission spectra of excited gas atomsBlackbody RadiationHeated objects emit light, where the ν(or λ) is T dependent.~1900 Max Planck suggested that the energy emitted by blackbody sources only occurs in fixed amounts.The smallest amt of E possible is a quantumwhose E ∝ νBlackbody Radiation (cont’d)High freq, ν, (short λ) has a high EThe proportionality constant is Planck’s constant, h, andE = hν where h = 6.63 x 10-34Js
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4Photoelectric Effect1905 – Einstein, trying to explain how light shining on a metal surface can generate an electric current, extends this ideato include light, which is a stream of tiny packets called photonsEphoton= hνPhotoelectric Effect (cont’d)Problem: A laser emits a signal with a wavelength of 351 nm. Calculate the energy of a photon of this radiation.Solution: Emission (line) SpectraWhite light thru a prism Æcontinuous spectrum (rainbow)Light is “bent” by prism, how much depends on λShorter λmore than longer λ