Photon as Electromagnetic Wave

We know that when an atom absorbs a photon with exactly the right energy, an electron will jump to a higher level. A photon, a particle of light, can be thought of as an electromagnetic wave with a particular oscillation frequency. Different photons have different frequencies along the electromagnetic spectrum. A low energy photon will have a lower frequency than a high energy photon. The precise energy of that photon defines the frequency of the oscillation in an atomic clock.