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Photoelectric Effect Photon

The photoelectric effect, from Wikipedia:

The photoelectric effect is the emission of electrons or other free carriers when light falls on a material. Electrons emitted in this manner can be called photoelectrons.
The photoelectric effect description often uses photons:

The photons of a light beam have a characteristic energy proportional to the frequency of the light. In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function (the electron binding energy) of the material, it is ejected. If the photon energy is too low, the electron is unable to escape the material.  ...  Thus, the energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy (equivalent frequency) of the individual photons. It is an interaction between the incident photon and the outermost electrons.

This description is the same as for absorption lines except the spectral line's  description stays with the frequency and intensity but avoids a photon.

A material's absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies. The absorption spectrum is primarily determined by the atomic and molecular composition of the material. Radiation is more likely to be absorbed at frequencies that match the energy difference between two quantum mechanical states of the molecules. The absorption that occurs due to a transition between two states is referred to as an absorption line and a spectrum is typically composed of many lines.

The frequencies where absorption lines occur, as well as their relative intensities, primarily depend on the electronic and molecular structure of the sample. The frequencies will also depend on the interactions between molecules in the sample, the crystal structure in solids, and on several environmental factors (e.g., temperature, pressure, electromagnetic field).

Both of these observations involve a material with defined energy states, a particular frequency of electromagnetic radiation or waves, at a particular intensity, and an observed result for that combination.

Electromagnetic radiation is always a wave. It is the propagation of synchronized perpendicular electric and magnetic fields and the wave has a specific frequency or wavelength and intensity.
A particle nature will arise only in an observation.
In the photoelectric effect a particle is ejected so the scientist is inclined to a particle leading to a photon 'particle' is in the description.
In the analysis of spectral 'lines' there is nothing to infer a 'particle' nature so the description is consistent with frequency and intensity but no photon.

A photon is in the eye of the observer depending whether the observation has a behavior associated with a particle.

I notice photons are mentioned more often, especially in less technical media, simply because it is so much easier than saying a 'specific wavelength at a specific intensity.'

I discussed photons in posts on 03/09 and on 03/10.

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