Photons always propagate With speed c. but light appears to travel at a speed different from c in dense media .how can we account for this phenomenon
This phenomenon can be explained by the fact that photons can interact with the atoms and molecules in the medium, resulting in a delay in their propagation. This delay can be seen as a slowing down of the effective speed of light in the medium.
When light travels through a medium, it encounters atoms and molecules that form the medium. These particles can absorb and re-emit the photons as they pass through, causing a delay in their propagation. This delay manifests itself as a reduction in the effective speed of light in the medium, which is known as the refractive index of the medium.
The refractive index is a measure of how much a medium slows down the speed of light. It can be expressed as the ratio of the speed of light in a vacuum to its speed in the medium, n = c/v. The higher the refractive index of a medium, the slower light will travel through it.
Thus, the apparent slowing down of light in dense media can be explained by the interaction of photons with the atoms and molecules in the medium, resulting in a delay in their propagation, and a lower effective speed of light in the medium.
The phenomenon you are referring to is called "slowing down of light" or "speed reduction of light in dense media." This can be accounted for by considering the interaction of light with the atoms or molecules in the medium.
In a vacuum, photons always propagate at the speed of light, denoted as "c," which is approximately 299,792,458 meters per second. However, when light enters a dense medium, such as glass or water, it interacts with the atoms or molecules making up the medium.
These atoms/molecules have charged particles, such as electrons, which are involved in the absorption and re-emission of light. When light interacts with these charged particles, it induces a temporary oscillation of the charges. As a result, the photons are absorbed and re-emitted multiple times, causing a delay in their propagation through the medium.
This absorption and re-emission process leads to a decrease in the effective speed at which the photons pass through the medium. It gives the perception of light traveling slower than it does in a vacuum. This reduced speed is often denoted as "v" and can be significantly lower compared to the speed of light in a vacuum.
Quantitatively, the speed of light in a medium can be related to the speed of light in a vacuum by the refractive index (n) of the medium. The relationship is given by:
v = c/n
where "v" is the speed of light in the medium, "c" is the speed of light in a vacuum, and "n" is the refractive index of the medium.
This phenomenon is a result of the intricate interaction between photons and the particles in the medium. It is important in various optical phenomena, such as refraction, where light changes direction when passing from one medium to another, and is fundamental to the operation of lenses, prisms, and other optical devices.