What quantum transition occurs inside a cool hydrogen atom to produce a 21-cm radio photon?
A) The electron combines with the proton in the nucleus to become a neutron,producing energy.
B) An electron reverses the direction of its motion in orbit around the proton.
C) An electron in the ground atomic state reverses its direction of spin with respect to that of the proton.
D) An electron falls from the level n = 100 to the level n = 99 in the atom.

Question

Quizplus · Accepted Answer

The 21-cm radio photon is produced when an electron in the ground state of a hydrogen atom undergoes a transition to an excited state with a different spin orientation. Specifically, the electron flips from having its spin aligned with the proton to having its spin anti-aligned with the proton. This transition corresponds to a change in energy of the atom, and the release of a photon with a wavelength of 21 cm.

What Quantum Transition Occurs Inside a Cool Hydrogen Atom to Produce