1 . A light source of wavelength, ( ? ), illuminates a metal and ejects photoele
ID: 2303372 • Letter: 1
Question
1. A light source of wavelength, (?), illuminates a metal and ejects photoelectrons with a maximum kinetic energy of 1.4 eV. A second light source of wavelength (?/2) ejects photoelectrons with a maximum kinetic energy of 5.5 eV. What is the work function of the metal? __________eV
2. How much total kinetic energy will an electron-positron pair have if produced by a 2.35 MeV photon? _________MeV
I just want the answer with the correct signs, please check the answer to make sure it is right. Thank you
Explanation / Answer
1) The maximum kinetic energy of the source is K1 = 1.4 eV
The wavelength of the second source is lambda / 2
The maximum kinetic energy of the source is K2 = 5.5 eV
From the equation of photo electric effect for the first source
hc / lambda = W + K1
And for the second source
2hc/lambda = W + K2
From the above two equations we get
2(W+ K1) = W + K2
2W + 2K1 = W + K2
W = K2 - 2K1
= 5.5eV - 2 * 1.4 eV
= 2.7 eV
--------------------------------
2) The electron an positron have the same mass-energy = 0.511 MeV.
Ephoton = 2(melectron/positron)c2+ KE
2.35 MeV = 2(0.511MeV) + KE
KE = 1.328 MeV
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.