# Resonate frequency of an object?

Below is a paragraph taken from the web site, physicsclassroom.com:

It is often useful to think of these electrons as being attached to the atoms by springs. The electrons and their attached springs have a tendency to vibrate at specific frequencies. Similar to a tuning fork or even a musical instrument, the electrons of atoms have a natural frequency at which they tend to vibrate. When a light wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational motion. (This is merely another example of the resonance principle introduced in Unit 11 of The Physics Classroom Tutorial.) If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it into vibrational motion.

Can the above be right? Wouldn't the vibrational frequencies of the electrons in atoms be just non classical? How could there be a natural frequency of the electrons that matches a light wave with the same natural frequency if one is non classical (the electron) and the other is classical (the light wave)?

Perhaps they have this all wrong and resonance just refers to vibrational frequencies of molecules matching specific light wave frequencies. But that idea seems unlikely since molecules just vibrate within the infra-red range. For example, I've heard that the human body has a resonant frequency around 68 Hz. I've heard all objects have a resonant frequency.

What is meant by the resonant frequency of an object?

• The classical model of electrons bound by elastic forces can be used to derive the dependency of the refractive index of a dielectric material from the frequency of the em radiation going through it. It may happen that classical and semiclassical models give results that are not that far off from what you can get from an experiment. Doing everything quantumechanically might not be the aim of a website like physicsclassroom. – Peltio Jun 24 '15 at 20:49
• Peltio -- But aren't orbitals inside an atom stationary; i.e. no real vibration (perhaps only that of a non classical type)? Just confused how those same orbitals could simultaneously have a classical vibration. – adam3033 Jun 24 '15 at 21:19
• @adam3033 - You need to keep in mind the old saying: All models are wrong, but some are more useful than others. The behavior of electrons as modeled by springs IS classical modeling. And for some purposes, such as the absorption of light by electrons, the classical model works pretty well. The quote which is giving you trouble is simply trying to provide an easy conceptual framework for the classical model. The concept of (sort of) stationary orbitals is very much non-classical. Don't try to mix the two - you'll just get a headache. – WhatRoughBeast Jun 25 '15 at 3:06
• WhatRoughBeast -- Definitely see what you're saying. Would the best way to describe it, though, be that even though electrons absorb it, the electron, itself, isn't that classical vibration? Just absorbs? – adam3033 Jun 25 '15 at 4:04