Question

Show your works and units for full credits 1. If the wavelength of a red light photon in vacuum is a = 680 nm, what is the energy of the photon in units of eV? (1 eV = 1.6 x 10-19 and Planck constanth 6.63 x 104 ) E- 2. What is the wavelength of a laser light beam that has the photon energy of 3.12 x 10-20 ? 2 3. If an electron moves a speed of 0.34c, then what is the non-relativistic de Broglie wavelength? (me=9.11 x 100 kg) 2- 4.. If the position of an electron in an atom is measured to an accuracy of 0.015 nm, what is the electron's minimum uncertainty in momentum? AP- 5. The work function for platinum is 6.35 V. (a) ir light of energy 1.25 x 10- is incident on platinum, what is the maximum kinetic energy of the ejected photoelectrons? Give the answer in units of joules. (b) Calculate the corresponding (non-relativistic) de Broglie wavelength of photoelectrons (m. = 9.11 x 1031 kg) KE..

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Answer 1

h (3.) de Broglie wavelength = mv here mis rest mass for non- relativistic 31 kg. rest mass of e me = • 9.11 x 10 moving velocity v = a. 34 c. d h me v 6.63 x 1034 9.11x10-31 x 0.34 X 3x108 1= 0.8 x 10 11 da 8x1010 m. d = 80 nm

2. (4.) By heisenberg Uncentainty principle ANWAR & h multiply sign. whe 2x 4 reduced plank constant. 0.015 nm here uncertainty in position Ax = 0.015 x 109 m. Лх = 1,5 x 10-11 ox. Ap = h 2T 1,5 x 10" x (ap) : 6.68x1034 9x3.14 Ap = 6.68 x 10²34 2 x 3.14 X 1,5 1011 -23 Др 0.7 x 10 Kg ms.' y uncertainty in momentum,

(5.) Einsteing photo lectric theory By this theory if a photonic energy of frequency v is incident the condition of ejection of photo on a metal then electron will be . v> Vo photon energy a work function here photon energy ho= 1.25 x 10 19 J. and work foundion wo = 6.35 x 1,6x1019 J. since Wosho work function > photon energy there will be no ejection of e. KEmar = O d = - (not found) ple uprote

(1) wavelength of red light photon d = 680 nm. 1 = 680 x 10 9 m. h = 6.63 x 10 34 Jos Energy of photon in space (vaccum) E ho - hc 0-34 6.63 x 10 680 x 10 9 x 3 x 108 E a 2.9 x 1019 J -19 lev IT 1.68 10 J. +19 IJE en 1 1.6 xlo E. 1019x lot19 N 2.9 1.6 E. 2,9 ev 1.6 LE 1.81 N

(2) photon energy = hu where v = I can be written as. beam. frequency of vi * where c = speed of light di wave leath of beam, he 3. 12 x 10 19 J. f = he 3.12 x 1019 La 6.63 x 1034 x 3 x168 3,12 x 1019 de -7 6.3 x 10 d= 0.063 nm