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PROBLEM SET 1 - Dr P Lucas U of A MSE 110 LIGHT E = h υ υ...

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Dr. P. Lucas U of A MSE 110 LIGHT E = h υ υ =c/ λ h: Planck constant h = 6.626x10 -34 J.s Duality wave/particle of the light: two possible descriptions • Electromagnetic Energy: Light
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Dr. P. Lucas U of A MSE 110 Problem 1 An Infrared laser emits photons of wavelength λ = 785 nm. What is the energy of these photons in Joules? (5 pts) [Answer in J] λ = ν = c h h E Joules 10 53 . 2 m 10 785 sec m 10 3 s J 10 626 . 6 E 19 9 8 34 × = × = Ans: where c = 3 × 10 8 m /sec, and λ = 785 × 10 -9 m Therefore,
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Dr. P. Lucas U of A MSE 110 Problem 2 What is the energy of the infrared laser photons ( λ = 785 nm) in eV? eV 583 . 1 J 10 6 . 1 eV 1 J 10 53 . 2 E 19 19 = × × = Joules 10 53 . 2 m 10 785 sec m 10 3 s J 10 626 . 6 E 19 9 8 34 × = × = Ans: The definition of an eV is the energy gained by an electron accelerated by a potential of 1 V. Therefore it is equal to one V times the charge of the electron, E = 1 V × 1.6·10 -19 C. Hence 1 eV = 1.6·10 -19 Joules
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Dr. P. Lucas U of A MSE 110 Problem 3 The energy of an Argon ion laser photon is 2.41 eV. What is its frequency? (5 pts) [Answer in Hz (s -1 )] eV J s J eV h E 19 34 10 6 . 1 10 626 . 6 41 . 2 = = ν Hz 10 82 . 5 sec 10 82 . 5 14 1 14 × = × = ν Ans: E=h ν hence
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