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Unformatted text preview: Prepared by Girma 1 Physics 214 Spring 2006 Solution to Homework ] 11 Problem 1. In the Bohr atomic model, the electron in hydrogen atom revolves around the nucleus containing the proton. Its total energy, when moving with speed v at a distance r from the proton, is then the sum of the kinetic and the potential energies, E = 1 2 mv 2 k e 2 r , (1) where m is mass of the electron, e is charge of the electron and k = 1 / (4 π² ) is Coulomb’s constant. The Coulomb force by the proton on the electron is central and causes centripetal motion, k e 2 r 2 = mv 2 r . (2) Bohr then postulated that the angular momentum of the electron should be quan tized as mvr = n ~ , (3) where n = 1 , 2 , 3 , ··· and ~ = h/ 2, h being Planck’s constant. Combining (2) and (3) gives quantized radii and velocities, r n = n 2 ~ 2 kme 2 and v n = ke 2 n ~ . (4) Putting these in the energy given by (1) gives quantized energies, E n = mk 2 e 4 2 n 2 ~ 2 = E 1 n 2 , where E 1 = mk 2 e 4 2 ~ 2 . (5) Putting in the numbers, E 1 = mk 2 e 4 2 ~ 2 = 9 . 11 × 10 31 kg (8 . 99 × 10 9 N.m 2 /C 2 ) 2 (1 . 60 × 10 19 C ) 4 2(1 . 05 × 10 34 J.s ) 2 = 2 . 19 × 10 18 J = 2 . 19 × 10 18 J × 1 . 60 × 10 19 eV 1 J = 13 . 6 eV. (6) When the hydrogen atom makes a transition from a higher energy level E n 2 to a lower energy level E n 1 , it emits a photon of energy hf = E n 2 E n 1 = ⇒ h c λ = E 1 ( 1 n 2 1 1 n 2 2 ) = ⇒...
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This note was uploaded on 09/25/2008 for the course PHYS 2214 taught by Professor Giambattista,a during the Spring '07 term at Cornell.
 Spring '07
 GIAMBATTISTA,A
 Energy, Work

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