If light is an electric and (magnetic field), how can it be absorbed?

Question

I was wondering how light or any electromagnetic radiation can be "absorbed" if it consists of electric and magnetic fields. For example if there is a charge at point A, and the light reaches point A, it will cause that charge to move depending on the value of the electric field. However, why wouldn't this electric field continue on and influence others particles everywhere else? For example, if you have a static charge creating an electric field, then if you put a charge at point A it will feel its effects and then if you bring a charge at another location B it will also feel its effects, namely it will not have been absorbed. Please shed some light on this. Thanks

edit: Does this mean the electron that absorbs this light moves in such a way that it creates an electric field of its own canceling the initial one? Or am I way off?

Answer 1

The situation with an incoming wave accelerating a charged particle (an electron) is the classical process known as Thomson scattering.

The electric field of the incoming wave exerts a (Lorentz) force on the electron. (Usually the magnetic component of the Lorentz force is ignored because the magnitude of ${\bf v} \times {\bf B}$ is small compared with ${\bf E}$ unless the electron is forced to move relativistically.)

Because the electron is accelerated in phase with the incoming EM wave, it oscillates and emits electromagnetic radiation as a classical oscillating electric dipole. Crucially, this radiation does not have to be emitted in the same direction as the incoming wave - in fact the electric field amplitude of the emitted radiation is azimuthally symmetric and scales as $\sin \theta$ in the polar direction (ie. no emitted field in the polarisation direction of the incoming electric field).

The net effect is to take energy out of the incoming "beam" and scatter it out of the original EM wave direction - a process that would be viewed as "absorption" by someone trying to view the original EM radiation.

You then compare this with static charge situations, but of course if they are static, then the charged particles are not accelerating and therefore cannot take energy out of the existing fields and turn it into electromagnetic radiation. In reality, if the charges are free to move in a vacuum, then the thought experiment you proposed would not happen like that. When you introduce another charged particle it will accelerate any other charged particles and energy will be taken out of the (pseudo-static) electric field.