Electromagnetic waves, such as light, behave differently in vacuum (empty space) compared to when they propagate through matter or materials. The main differences arise due to the interaction of electromagnetic waves with the atoms or molecules present in the medium.
In Vacuum:
- Speed: In vacuum, electromagnetic waves travel at the speed of light, which is approximately 3 x 10^8 meters per second (m/s) in a vacuum. This speed is a fundamental constant of nature denoted by 'c'.
In Matter/Materials:
Speed: When electromagnetic waves propagate through a medium, their speed is generally lower than the speed of light in vacuum. The speed of light in a medium is denoted by 'v', and it depends on the properties of the medium, such as its refractive index. The refractive index of a material is the ratio of the speed of light in vacuum to the speed of light in that material. Thus, the speed of light in a medium is given by v = c/n, where 'n' is the refractive index of the material.
Absorption and Scattering: Matter can absorb or scatter electromagnetic waves as they pass through. The interaction between the waves and the atoms or molecules in the material can lead to energy loss or redirection of the wave's path. This absorption and scattering behavior depends on the nature of the material and the frequency of the electromagnetic waves. Different materials have different absorption and scattering characteristics, which can be utilized in various applications, such as optical filters or lenses.
Refraction: Refraction is the bending of electromagnetic waves as they pass from one medium to another. When light travels from one material to another, its speed changes due to the difference in refractive indices. This change in speed causes the light to bend at the interface between the two materials. The amount of bending depends on the angle of incidence and the refractive indices of the materials involved. Refraction is responsible for phenomena like the apparent bending of a straw in a glass of water.
Dispersion: Materials can cause different frequencies of light to travel at different speeds, resulting in dispersion. Dispersion leads to the separation of white light into its constituent colors when passing through a prism. This effect is due to the dependence of the refractive index on the wavelength (or frequency) of the electromagnetic wave.
These are some of the key differences between the behavior of electromagnetic waves in vacuum and in matter/materials. The interaction of electromagnetic waves with matter gives rise to a wide range of optical phenomena and is the basis for many technological applications.