The following data were collected in a laboratory study of photoionization
PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation
Problem
The following data were collected in a laboratory study of photoionization.
A monochromatic beam of ultraviolet light was directed, one sample at a time, at low-pressure gases of two unknown elements, X and Y. For each element, the longest wavelength capable of liberating an electron from a ground-state atom was measured. The results are summarized below.
• Element X longest ionizing wavelength λX=91.1nm
• Element Y longest ionizing wavelength λY=157nm
Assume each atom is initially in its ground state. Use the following constants where needed: speed of light c=3.00×108ms−1, Planck constant h=6.63×10−34Js, 1eV=1.60×10−19J.
(a) Calculate the binding (ionization) energy of a ground-state atom of element X in electron-volts.
(b) Calculate the binding (ionization) energy of a ground-state atom of element Y in electron-volts.
(c) Rank the two elements according to the magnitude of their binding energies, from greatest to least. Justify your ranking in terms of the photon characteristics required for ionization.
(d) A separate ultraviolet source produces photons of wavelength 75nm. Determine for each element whether these photons will ionize a ground-state atom. Support your answer with quantitative reasoning.