por What is the refraction of light?
The light refraction It is the optical phenomenon that occurs when light falls obliquely on the separation surface of two media, liquid or gas, with different refractive index. When this happens, the light changes its direction and its speed.
Refraction occurs, for example, when light passes from air to water, since it has a lower refractive index. It is a phenomenon that can be perfectly appreciated in the pool, when observing how the shapes of the body under water seem to deviate from the direction they should have.
It is a phenomenon that affects different types of waves, although the case of light is the most representative and the one that has the greatest presence in our day to day.
The explanation of the refraction of light was offered by the Dutch physicist Willebrord Snell van Royen (1580-1625), who established a law that has come to be known as Snell’s law.
Another of the scientists who paid special attention to the refraction of light was Isaac Newton (1643-1727). To study it he created the famous glass prism. In the prism, light enters it through one of its faces, refracting and decomposing into different colors. In this way, through the phenomenon of light refraction, he proved that white light is made up of all the colors of the rainbow.
elements of refraction
The main elements that must be considered in the study of light refraction are the following:
The incident ray, which is the ray that falls obliquely on the separation surface of the two physical media.
The refracted ray, which is the ray that crosses the medium, changing its direction and speed.
The normal line, which is the imaginary line perpendicular to the surface of separation of the two media.
The angle of incidence (i), which is defined as the angle between the incident ray and the normal.
The angle of refraction (r), which is defined as the angle formed by the normal with the refracted ray.
One must also consider the refractive index (n) of a medium, which is the quotient of the speed of light in a vacuum and the speed of light in the medium.
n = c/w
In this regard, it should be remembered that the speed of light in a vacuum takes the value of 300,000,000 m/s.
Refractive index of light in different media
The refractive indices of light in some of the most common media are:
Laws of refraction
Snell’s law is often referred to as the law of refraction, but the truth is that it can be said that there are two laws of refraction.
first law of refraction
The incident ray, the refracted ray and the normal are in the same plane of space. In this law, also deduced by Snell, reflection also applies.
second law of refraction
The second law of refraction, or Snell’s law, is determined by the following expression:
n1 sin i = n2 sin r
Being n1 the refractive index of the medium from which the light comes; i, angle of incidence; n2 the refractive index of the medium in which the light is refracted; r, the angle of refraction.
Fermat’s principle
From the principle of minimum time, or Fermat’s principle, both the laws of reflection and the laws of refraction, which we have just seen, can be deduced.
This principle states that the real trajectory followed by a ray of light that travels between two points in space is the one that requires the shortest time to travel.
Consequences of Snell’s Law
Some of the direct consequences that can be deduced from the previous expression are:
a) if n2 >n1 ; sin r < sin i let r < i
So when a A ray of light passes from a medium with a lower refractive index to one with a higher refractive index. refractive index, the refracted ray approaches the normal.
b) if n2
So when a A ray of light passes from a medium with a higher index of refraction to one with a lower index. the refracted ray moves away from the normal.
c) If the angle of incidence is zero, then the angle of the refracted ray is zero.
Limit angle and total internal reflection
Another of the important consequences of Snell’s law is what is known as limit angle. This is the name given to the angle of incidence that corresponds to a refraction angle of 90°.
When this happens, the refracted ray moves flush with the separation surface of the two media. This angle is also called the critical angle.
For angles greater than the limit angle, the phenomenon called total internal reflection occurs. When this occurs, no refraction occurs, since the entire light beam is internally reflected. Total internal reflection only occurs when going from a medium with a higher refractive index to a medium with a lower refractive index.
One application of total internal reflection is the conduction of light through the optical fiber without loss of energy. Thanks to it, we can enjoy the high data transfer speeds offered by fiber optic networks.
experiments
A very basic experiment to observe the phenomenon of refraction consists of introducing a pencil or a pen into a glass full of water. As a result of the refraction of light, the submerged part of the pencil or pen appears slightly broken or deviated with respect to the trajectory that one would expect it to have.
You can also try a similar experiment with a laser pointer. Of course, it is necessary to pour a few drops of milk into the glass of water to improve the visibility of the laser light. In this case, it is recommended that the experiment be carried out in low light conditions to better appreciate the path of the light beam.
In both cases, it is interesting to try different angles of incidence and observe how the angle of refraction varies as they change.
Causes
The causes of this optical effect must be found in the refraction of light that causes the image of the pencil (or the beam of light from the laser) to appear deviated underwater with respect to the image we see in the air.
The refraction of light in everyday life
The refraction of light can be observed in many situations of our day to day. Some we have already named, others we discuss below.
One consequence of refraction is that pools appear to be shallower than they really are.
Another effect of refraction is the rainbow that occurs when light is refracted when passing through the water droplets present in the atmosphere. It is the same phenomenon that occurs when a beam of light passes through a prism.
Another consequence of the refraction of light is that we observe the sunset of the Sun when several minutes have passed since it actually happened.
https://youtu.be/nE4ZPDHOQWg
References
Light. Retrieved from en.wikipedia.org.
total internal reflection. Retrieved from en.wikipedia.org.
Light. Retrieved from en.wikipedia.org.