When constructing an energy-level diagram from measured emission wavelengths
PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
When constructing an energy-level diagram from measured emission wavelengths, a student chooses to set the ground-state energy equal to 0eV instead of setting the ionization limit at 0eV. Which of the following best explains why this choice does not affect any physical predictions?
(a) Using the ionization limit as zero would reverse the sign of all photon energies, producing negative photon energies that are not allowed.
(b) The ground state must be the reference because photon energies are always measured relative to the vacuum level.
(c) Only energy differences are physically measurable, so shifting the entire scale by a constant amount leaves all transition energies unchanged.
(d) Choosing the ground state as zero artificially increases all excited-state energies, which would make the calculated wavelengths shorter.