Electromagnetic Radiation
An atom receives a burst of energy which may come in a flush of heat. An electron absorbs the energy bit, boosting it to a higher orbital, farther from the nucleus. But the electron cannot hold that position for more than a fraction of a second, and so it falls back to its original shell.
An electron losing energy, as happens when dropping to a lower orbital shell, results in releasing that energy as a photon. How much energy a released photon has depends upon how far the electron dropped between orbitals. That determines the photonic wavelength.
In this case, wavelength is spatial period of an energy wave: the point-to-point distance between wave repetitions. Mathematically, wavelength (l) is the spatial period of a sine wave.
The energy of a single wavelength is a product of its mass, angular frequency, and amplitude (height). The mass of a wave defines its momentum.
The wavelength gives the angular frequency, which is the rate of change in the wave. The shorter the wavelength, the higher its frequency and greater its energy.
Electromagnetic radiation is a wave of radiant energy. The photon is its quantum poster child.
