If light is an electric and magnetic field how can it be absorbed(dont mark as duplicate)? [duplicate]

Question

This question was answered here previously but i am re asking it since it a was no explained in detail I actually want to know the energy stored in electromagnetic waves move to the electron and gets scattered in different direction(Thomson scattering)how cum energy stored in field moves to the electron does the electron create opposite em wave which cancel the original wave so energy is bsorbed or any differnt phenomenan takes place please explain in detail

Answer 1

This is discussed in my answer to the question Cause behind photoelectric effect. That specifically asks how energy is transferred from the light wave to the electron in the photoelectric effect, but the basic mechanism is the same for all types of light absorption.

A light wave has an oscillating electric field - there is also an oscillating magnetic field but this is usually not important in light absorption. If the light wave passes by an electron the oscillating electric field will exert a force on the electron and the electron will oscillate in response. So we have now transferred some of the energy of the light to kinetic energy of the electron.

What happens next depends on the situation. For a light ray passing through a transparent medium the oscillating electron reradiates the light so the energy originally taken from the light is returned to it and the energy of the light ray is unchanged. However the oscillating electron may reradiate the light with a phase lag, which is the reason the medium can have a refractive index greater than one.

Alternatively the energy of an oscillating electron may be transferred into a change in potential energy, which is what happens when an electron in an atom is excited by light. In this case the light produces a transient oscillating charge then a change in the potential energy of electron leaving it in a different atomic orbital.

Answer 2

Yes, in the shadow behind a black screen the field is a superposition of the incident light and the field from the electrons in the material of the screen. We see that the sum is zero, so that induced field must be opposite to the incident field. (This also explains Babinet's principle, that a wire gives the same diffraction patterns as a slit.)

A way to visualize what is happening in the screen classically is to regard the material as a collection of classical Lorentz oscillators: charge masses on a spring with some damping. These oscillators have a resonant frequency. When the frequency of the light is far below resonance, the material is transparent (with a lower phase velocity). When the frequency gets closer to resonance, the amplitude of the induced motion increases, the index of refraction gets higher. But at resonance, the phase changes, and there is absorption.

Answer 3

I actually want to know the energy stored in electromagnetic waves

One has to keep clear the two frameworks, classical and quantum mechanical. Light is a classically described concept using classical Maxwell's equations.

move to the electron and gets scattered in different direction(Thomson scattering)

The electron is a quantum mechanical entity and needs quantum mechanical equations for a correct description.

Classical electromagnetic waves and the energy they carry are an emergent phenomenon. ( a mathematically similar phenomenon is the emergence of thermodynamics from statistical mechanics, but here we have to deal with the quantized state)

This picture may give you an intuition:

It is how a circular polarized classical wave ( the red arrow on the left is the electric field) emerges from the zillions of photons that compose it, in the middle the photon that just has a spin backwards or forwards , energy hν, and mass zero. On the right the wavefunction of the photon is shown, for the relevance to polarization. The wavefunctions add up in superposition, and then the $ψ*ψ$ of the whole ensemble will give the polarization of the classical beam. The spin of the photons, correlated to the left and right polarizations.

So the photon is connected to the electric and magnetic fields through the complex wavefunction

which is a solution of a type of quantized maxwell's equation.

Electrons interact with the incoming photons of the beam in Feynman diagrams of the type :

A Feynman diagram representing the γe→γe process. In the classical limit, this is called Thomson scattering. The quantum version is called Compton scattering, and in the relativistic regime, the result is given by the Klein-Nishina formula.

Collectively the superposition of the individual interactions will build up the observed classical behavior , which is given by the $ψ*ψ$ of the whole ensemble. It is evident, that since the classical descriptions are so successful , the classical solutions are used for most electromagnetic interactions. The quantum mechanical calculations are reserved for few particle interactions and high energy photons.

how come energy stored in field moves to the electron

it is transferred by individual photon scatters

does the electron create opposite em wave

No. In any case Thomson scattering is an elastic scattering as shown above, just directions change of particles (photons and electrons) and the new beam emerging from the scatter has the form of Thomson or Rayleigh scattering. More compicated interactions can occur, changes of energy levels of electrons or molecules on the lattice, but that is another complicated story that is best described with the classical em solutions. One does not use a scalpel( QM) to dig a ditch(classical).