When introducing the Bohr atom it is a good idea to review standing waves for the students, for example with Rudnick's String [1]. You can show how the string resonates for various harmonics as the driving frequency is changed.
Another demonstration puts standing waves on a circular wire loop - standing waves around a circle. A mechanical wave driver controlled by a function generator shakes the loop at the bottom and it resonates with an odd number of antinodes on the circle at the frequencies:
Number of antinodes | Frequency (Hz) |
3 | 18 |
5 | 65 |
7 | 140 |
9 | 237 |
Links:
[1] https://demoweb.physics.ucla.edu/node/278