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lecture_8_07b

# lecture_8_07b - Quantum Planck's constant h = 6.56 x10-34 J...

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05/11/09 Physics 13 - Fall 07 - G.R. Goldstein 1 Quantum Planck’s constant h = 6.56 x10 -34 J s = 4.14x10 -15 eV s very small number! e.g. Visible light: λ = 0.600 μ m = 600 nm so ν =c/ λ = 5x10 14 sec -1 and E = h ν ≈ 4x10 -19 J ≈ 2 eV cf. kT at T=290 K is 1.38x10 -23 x 290 ≈4.0x10 -21 J ≈ 2.5x10 -2 eV

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05/11/09 Physics 13 - Fall 07 - G.R. Goldstein 2 Photoelectric effect (Hertz 1887) Fix V across tube Measure i(current) vs. ν (frequency), light intensity Ι Vary V(voltage) cathode anode light e -
05/11/09 Physics 13 - Fall 07 - G.R. Goldstein 3 Current vs. Voltage Max i at highest light Intensity Max i at low I i(current) V -V s Stopping potential independent of I, varies with ν

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05/11/09 Physics 13 - Fall 07 - G.R. Goldstein 4 Interpretation of i and V S • 1/2 mv max 2 = eV S • So v max is independent of Ι (power/area) electrons can not absorb all Ι Einstein(1905): Light = photons = quanta and E = h ν Wave-particle duality • eV S = 1/2 mv max 2 = h ν - φ where φ is the work function of the metal in cathode
05/11/09 Physics 13 - Fall 07 - G.R. Goldstein 5 Work function V S ν ν C = φ /h Slope h/e

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lecture_8_07b - Quantum Planck's constant h = 6.56 x10-34 J...

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