When light travels through a medium, such as a transparent material like glass or water, its speed is reduced compared to its speed in a vacuum. This reduction in speed is due to the interaction of light with the atoms or molecules in the medium.
Light consists of electromagnetic waves, which are made up of oscillating electric and magnetic fields. When these waves encounter atoms or molecules in a medium, several interactions take place:
Absorption and re-emission: The electric field of the light wave interacts with the charged particles (electrons) in the atoms or molecules. This interaction can cause the electrons to absorb energy from the light wave and move to higher energy levels. The energy is then re-emitted as the electrons return to their original energy levels. However, there is a delay between absorption and re-emission, which contributes to the slowing down of the overall propagation of light through the medium.
Scattering: Light can also scatter off the charged particles in the medium. This scattering occurs when the incoming light wave interacts with the charged particles and changes direction. Scattering can happen in various ways, such as Rayleigh scattering or Mie scattering, depending on the size and structure of the particles relative to the wavelength of light.
These interactions between light and the atoms or molecules in the medium cause a delay in the propagation of the electromagnetic waves, effectively slowing down the speed of light. The speed of light in a medium is determined by the optical properties of the material, including its refractive index, which is a measure of how much the medium can slow down light.
It's important to note that even though some photons may interact with the atoms or molecules in the medium, they are not "missing" the nucleus. The interaction occurs with the electrons surrounding the nucleus, as electrons are the charged particles that are directly involved in the electromagnetic interactions with light.
In summary, the slowing down of light in a medium is due to the interactions between the electromagnetic waves of light and the charged particles (electrons) in the atoms or molecules of the medium, including absorption, re-emission, and scattering processes. These interactions cause a delay in the propagation of light and reduce its speed compared to its speed in a vacuum.