# What is absorption of an electromagnetic wave?

Can any one explain the absorption/transmission/reflection of electromagnetic waves in the wave form? It is generally said that the atom absorbs/reflects/transmits photon. But can this phenomena be explained in the wave form of EMR?

• I am seriously looking for the answer in atomic level i.e the interactions of the electrons and nucleus dipole with the EMR. Can absorption be explained as the result of the in-phase dipole interaction and transmission as a result of partially out of phase interaction and reflection as a result of 180 degree out of phase interaction between atomic dipole and EMR? – Rams May 14 '14 at 16:10
• What type of answer are you looking for when you say explain in "wave form"? Have you only studied classical mechanics? – user6972 May 14 '14 at 17:13
• All my search for the basic concept behind the absorption and reflection ended with the explanation that the electron absorbs the photon and excites and release the photon. But i am looking for an explanation that would explain me how does the electron absorb a varying magnetic field? is my intuitive understanding that the electron proton dipole rotates in the varying magnetic field thereby producing phase/out of phase EM fields which is observed as absorption/reflection true? – Rams May 15 '14 at 15:02
• the field is related to the charge in motion. Electrons have their own EM fields and so do photons. How these interact (classically) is how the reflection/absorption process is modeled. This is a very broad topic and the answer that would "satiate" you could take years depending on your level of math and if you want to move beyond classic descriptions. The topics suggested by Ján Lalinský are a good start. If you have a more specific question then, come back and ask. – user6972 May 15 '14 at 22:28
• Here's a short youtube video of the Lorenz and Drude models which are a basic intro to the concept so you can get an idea of where you are on the learning curve before jumping into the more modern theories. youtube.com/watch?v=MBH5-oHqzp4 – user6972 May 15 '14 at 22:35

## 1 Answer

But can this phenomena be explained in the wave form of EMR?

Yes, these phenomena are usually described and explained using continuous EM field both in macroscopic and microscopic theory. The simplest thing of this kind is perhaps calculation of index of refraction and absorption coefficient based on calculation of expected average electric moment of atoms/molecules in EM field from the Schroedinger equation. If the field oscillates, so does average electric moment and the derived polarization. This is part of the theory of optical spectra of molecules.

• Thanks Jay for some insights. It would be grateful if i were provided with some exhaustive article that would satiate me of my yearn to know it. – Rams May 15 '14 at 17:12
• Search for these keywords - the Lorentz-Drude classical theory of dispersion, index of refraction, quantum theory of dispersion, time-dependent perturbation theory, oscillator strengths. I do not really know of any especially appropriate article - most of this stuff is in good textbooks on EM theory and in older books on wave mechanics (new books seem to skip or skim through this). Schroedinger explains dispersion in gases and their emission lines in his papers in book Collected papers on wave mechanics, Blackie and Son, 1928, papers II and IV. – Ján Lalinský May 15 '14 at 20:22
• Sokoloff discusses these things in his book Quantum Mechanics, 1966, sec. 14.F. For macroscopic theory of dispersion/absorption, Jackson's book Classical electrodynamics is OK. – Ján Lalinský May 15 '14 at 20:23
• @JánLalinský you should edit your answer with the updates as comments get removed over time. – user6972 May 15 '14 at 22:30
• @JánLalinský: Thanx that was useful. I could go through the video with good comprehension. So i look forward to read it though, for the theory. Turning to stack exchange was helpful. Atcually i have imagined an electron rotating that would create a rotating dipole which produces varying EM fields. So it is more about electron cloud rather than electron itself. I think we are far away from assuming a physical electron motion – Rams May 16 '14 at 17:49