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

Question

Quizplus · Accepted Answer

The 21-cm radio photon is produced by the hyperfine transition in which the electron in the hydrogen atom flips its spin from being parallel to the proton's spin to being antiparallel. This is a very low-energy transition and is not related to the electron changing energy levels in terms of its orbit around the nucleus.

What Quantum Transition Occurs Inside a Hydrogen Atom to Produce