White light passes through a sealed tube containing low-pressure sodium vapor
PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
White light passes through a sealed tube containing low-pressure sodium vapor, producing dark lines at the same wavelengths as the bright yellow doublet observed when the tube is excited electrically. Which of the following best explains this coincidence?
(a) Sodium atoms absorb photons that have enough energy to ionize the atoms, so those wavelengths are removed from the beam.
(b) Sodium atoms absorb photons whose energies exactly match allowed electronic transitions, and the same transitions emit photons of those wavelengths when the atoms later de-excite.
(c) Frequent collisions between sodium atoms scatter yellow light out of the beam, leaving dark lines that coincide with the light the atoms fluoresce.
(d) The sodium atoms absorb the yellow photons and dissipate their energy as heat through atomic vibrations rather than re-emitting them, so only those wavelengths are missing.