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[Q10] (5 + 5 = 10 Points) The visible spectrum of electromagnetic wave approximately, which spans between 350 nm to 750 nm, falls on a metallic surface. The work function for this metallic surface is 2.55 eV. Find the followings: (a) The spectral range that will successfully eject photoelectrons from the metallic surface. (b) The speed of the ejected electrons. 2

Answer 1

Amin 1240 eN nm no minimum wavelength of photon is Amen = 350nm .: Maximum energy of a phoston is Emas he Emax 350nm Emax = 3.543eV Mascimum wavelength of phalon is Amaziz 7Somm Corresponding energy of that photon és Emon Imas Emin = 1.653 eV @ Work function of metal is 140=2. 2.55eu If cut off wave. elength is dc then, Xc he 2.55et ~486.3 nm > maximum wavelength 1240 Nam 750 nm 1240 ex nm Aca of a photon which can eject election from the metal So, spectral range is (x=350nm to &=486.3nm Maximeum kinetic energy b of ejected electron is kiemas = 1 me on max Emax to
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» Umax = 34.88x1010 2 Uman 2 where, o mare is maxe mum speed of ejected electron. t me vimax = (3.543 —2,55)V 3x9.11x10 3" ophone 0.993x1.6x1519 = 2x0.993x1-6*10-19 9.11% 103 Umane = (J34.88x105 m/s Timax = 5.9x105m/s So, speed of ejected electron lie befroeen omis to 5.9x105 m/s.