Understanding Light: Electromagnetic Waves, Reflection, and Refraction
The Nature of Light: Electromagnetic Waves
In 1860, Maxwell published his mathematical theory of electromagnetism, which predicted the existence of electromagnetic waves that propagated at the same speed as light.
Therefore, he argued that light and other waves, such as radio waves, consisted of the same phenomenon: electromagnetic waves that differed only in frequency.
Today, we consider an electromagnetic wave to be unique, as it is composed of two disturbances: a vibrating electric field perpendicular to a magnetic field.
The Photon: Particle of Light
Einstein contributed greatly to our understanding of light. He not only proved that the speed of light in a vacuum (approximately 300,000 km/s) cannot be exceeded, but also introduced the idea of light quanta.
The Photoelectric Effect
A curious phenomenon is that electrons on the surface of some metals emerge when light is incident on them. It was discovered that these electrons had an energy that never exceeded a maximum.
Thus, it was argued that the electrons only absorbed a quantum of energy, i.e., a photon, so that increasing the frequency of the incident light results in more electrons being emitted per unit of time, but their energy will not increase because they have all absorbed the same amount: one photon.
Light Reflection
When light falls on an object, it returns to the medium to a greater or lesser extent. This phenomenon is called reflection, and thanks to it, we see things.
Diffuse Reflection
Diffuse reflection is typical of granular substances such as powders. For diffuse reflection, the rays are reflected in different directions due to surface roughness.
Mixed Reflection
Many reflections are a combination of specular and diffuse types. One manifestation of this is an extended reflection that has a dominant directional component that is broadcast in part by surface irregularities.
Mixed reflection is a combination of specular, spread, and diffuse reflection. This mixed type of reflection occurs in most real materials.
Spread Reflection
Spread reflection is one that cannot be associated with Lambert’s Law or the Law of Reflection. The illustration of reflection models below shows a possible model of spread reflection.
Light Refraction
When light passes from one transparent medium to another, there is a change in its direction due to the different speeds of propagation that light has in different materials. This phenomenon is called refraction.
Light Dispersion
When we look at a rainbow, we can see the colors that make up white light.
This phenomenon, known as dispersion, occurs when a light beam is refracted in some composite medium and separates into its constituent colors.
In the case of the rainbow, light is scattered when passing through water droplets.
The cause of dispersion is that the refractive index decreases with increasing wavelength, so that the longer wavelengths (red) deviate less than the shorter ones (blue).
Light Polarization
Light waves are rarely polarized, so that the electromagnetic vibration occurs at all levels. Light that vibrates in one plane is called polarized light.