What is light reflection?
The reflection of light consists in the change of direction of the light beam as soon as it reaches a surface and there it bounces, that is, it is reflected. Thanks to this, objects that normally do not emit their own light become visible.
If the surface is highly polished and smooth, like a mirror, the reflection allows an image to form of the object in front of it.
In this way, a person observes his image every morning in the bathroom mirror and this happens because light is a wave, and as such it obeys the law of reflection. The rays of light that come from a source such as the Sun , are reflected on the person and continue towards the mirror, in which they are reflected again and are captured by the eye. examples of reflection of light
The reflection of light also allows you to appreciate the colors of things. When an object is seen of a certain color, it is because it absorbs all the wavelengths except one, which the eye perceives and interprets as having a certain color. This is what happens with the sky, which is blue because that is the wavelength reflected by the molecules that make up the atmosphere.
Waves other than light also experience reflection when they change from one medium to another, for example sound. The effects are perceived in a different way, of course, but the physical principle is common to all these phenomena.
How is the reflection of light produced?
What is observed experimentally is that the light beam is reflected off a polished surface, with an angle of reflection of the same value as the angle of incidence.
The reflected beam has the same wavelength as the incident beam, for this reason the colors of the image are the same as the real object.
On the other hand, the line normal to the surface that passes through the point of incidence P, as well as the incoming and reflected rays are all in the same plane, called the plane of incidence.
The behavior of light described above can be summarized in the two laws of reflection as follows:
1.- The angle of incidence θ i is equal to the angle of reflection θ r :
θ i = θ r
2.- The incident ray, the reflected ray and the normal to the specular surface are all in the same plane (see figure 2).
Types of reflection and examples
Light is reflected to a greater or lesser extent on a surface, but some allow imaging and others do not, it depends on how smooth and polished the surface is. Two types of reflection are distinguished: examples of reflection of light
Specular reflection examples of reflection of light
Specular reflection occurs on flat, well-polished surfaces such as mirrors, highly polished metal surfaces, and calm bodies of water such as lakes.
Stained glass windows
Specular reflection also occurs in smooth and transparent stained glass, but due to transparency, a part of the incident light is transmitted to the other side, making it possible to see what is on the other side. On the other hand, in an ordinary flat mirror almost all the incident light is reflected.
The more normal the incident beam angle (closer to perpendicular), the greater the transmission. On the other hand, if the beam is directed rather grazing, the proportion of reflected light is greater. examples of reflection of light
Reflection in lakes and ponds
Specular reflection is a natural phenomenon that facilitates personal grooming on a daily basis and produces images of great beauty, such as when the sky and mountains are reflected on the quiet surfaces of lakes and ponds.
On optical devices examples of reflection of light
Reflection is also used to make mirrors that are part of a multitude of optical devices: telescopes and microscopes, to name a few, properly redirecting and concentrating light rays.
There are surfaces that, no matter how smooth they seem at first sight and to the touch, when viewed with a microscope, they show irregularities, such as a sheet of paper for example.
The law of reflection θ i = θ r is fulfilled in the same way as it does for specular surfaces, only there is no single normal line, because of the irregularities. This is why the angles of reflection are varied, and light is reflected in many different directions.
Whenever the surface roughness is greater than the wavelength of the incident light, diffuse reflection occurs, otherwise the reflection is specular. examples of reflection of light
The roughness of the surface is estimated by considering the microscopic elevations that it presents: if the distance separating successive elevations is less than one eighth of the wavelength of the incident light, the surface is considered to be polished.
Since most objects do not emit their own light, diffuse reflection is highly desirable to make objects visible from any direction.
The next time the reader is out for a walk, they may observe the following everyday examples of light reflection.
Columns in water bodies
When it comes to the reflection in the water of light sources such as the Sun, the Moon or the lights of the city, the typical columns of light are produced in the water.
It is because the surface of the water, even if it is calm, ripples smoothly, behaving like a set of mirrors instead of just one. These mirrors have changing orientations and each has a slightly different reflected image. examples of reflection of light
Columns on the wet pavement
Columns of light are also formed on the pavement of rain-damp streets, thanks to public lighting, traffic lights and vehicle lights.