A sealed discharge tube contains a dilute vapor of a single-element gas

PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation

Problem

A sealed discharge tube contains a dilute vapor of a single-element gas. When the gas is exposed to monochromatic light of wavelength 250 nm250\,\text{nm}, electrons are barely liberated from ground-state atoms. Fundamental constants: c=3.00×108 m s−1c = 3.00\times10^{8}\,\text{m\,s}^{-1}, h=6.63×10−34 J sh = 6.63\times10^{-34}\,\text{J\,s}, 1 eV=1.60×10−19 J1\,\text{eV}=1.60\times10^{-19}\,\text{J}. (a) Determine the binding energy of a ground-state atom of this gas in both joules and electron-volts. (b) Calculate the minimum photon frequency required to ionize a ground-state atom of the gas. (c) In a separate experiment the gas is first excited so that its electrons are 1.50 eV1.50\,\text{eV} below the ionization limit. Determine the longest wavelength light that can now ionize an atom in this excited state.

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