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# Msols - Physics 17 Fall 2009 T Tomboulis MIDTERM SOLUTIONS...

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Unformatted text preview: Physics 17 Fall 2009 October 30, 2009 T. Tomboulis MIDTERM SOLUTIONS 1. [10 points ] The electron in a hydrogen atom is initially in the second excited state state ( n = 3). 1. What is the longest wavelength of light it could absorb? 2. Suppose the electron absorbs a 17 eV photon. What is the kinetic energy of the ejected electron? 1. hf = hc λ = | E i- E f | , so the longest wavelength will result from the smallest possible ( E f- E i ) difference, i.e. transition to the next level n = 4: 1 λ = 13 . 6 eV c h 1 3 2- 1 4 2 = R 1 3 2- 1 4 2 which gives: λ = 144 7 1 R = 1875 × 10- 9 m 2. Ground state energy E 1 =- 13 . 6 eV. Electron in n = 3 level: E 3 =- 13 . 6 3 2 eV. E ∞ = 0. So electron gets enough energy to be ejected with K.E.: K = 17 eV- 13 . 6 3 2 eV = 15 . 49 eV 1 FALL 09, PHYS 17 Midterm Solutions 2. [10 points ] (A) A particle is confined in a box of equal edge lengths L , L 2 in the x , y and z directions, respectively. Estimate the energy of the particle. How will your estimate change if L is reduced to 10- 2 L ?...
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Msols - Physics 17 Fall 2009 T Tomboulis MIDTERM SOLUTIONS...

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