The reflection and refraction of light are two physical phenomena that can experience a ray of light. In reflection, the ray of light bounces off a surface, while in refraction the ray of light passing from one medium to another changes its angle of propagation.
|Light reflection||Refraction of light|
|Definition||Optical phenomenon where the ray of light bounces when it encounters a material.||Optical phenomenon where the ray of light changes direction as it passes through a medium of different density.|
|Medium||It occurs in the same medium||It occurs at the boundary between two media of different density|
n1. sin (α2) = n2. sin (α2)
Double image in aquariums
What is light reflection?
The reflection of light is the phenomenon that occurs when we have the feeling that a flash of light bounces on a surface.
What actually happens is that the ray of light returns when it collides with a medium other than the one it is moving, as would happen when a ball is stepped on a wall.
In the reflection of the light the original ray or can be distinguished lightning incident and the ray that becomes or lightning reflected. At the point where the incident and reflected rays meet, an imaginary line is drawn perpendicular to the surface known as normal.
The angle of incidence is formed between the incident ray and the normal, and the angle of reflection is formed between the normal and the reflected ray. Thus, the direction in which light is reflected depends on the shape of the reflecting surface and the direction of the incident beam.
Light has a wave frequency and a speed that is equal to both the incident ray and the reflected ray. However, the intensity of the reflected light is lower than the incident light.
Laws of light reflection
The laws of light reflection explain the propagation of the ray of light when it returns. There are two laws:
- First law: the incident ray, the normal to the incident surface and the reflected ray are in the same plane.
Second law: the angle of incidence α and the angle of reflection β are equal. If the angle of incidence is 30 ° C, the angle of reflection is 30 ° C. If the light strikes perpendicularly, the angle of incidence and the angle of reflection are equal to 0 ° C, so the light will be reflected by reversing the direction of propagation.
Examples of light reflection
The reflection of light passes into nature in many situations and with various applications.
In many places sunlight is used for cooking, through solar ovens, designed with polished curved surfaces that reflect and concentrate the rays in a small area.
The National Center for Scientific Research in France built a solar oven in Odeillo to study the properties of materials in environments with high solar temperatures. This furnace is based on the concentration of the sun’s rays by reflection, reaching 1000 kilowatts per square meter.
Formation of images in mirrors
A mirror is a smooth surface where light beams bounce off and an image is formed by the effect of light reflection. The most common mirrors are flat mirrors made from a piece of glass covered on one side with silver or aluminum nitrate.
A kaleidoscope is an optical instrument that consists of a tube with interior mirrors and pieces of colored glass. As the kaleidoscope is rotated, figures of various multicolored patterns are formed, as a result of the reflection of light inside the toy.
Total internal reflection
Total internal reflection is a special reflection that can be observed in gems, such as diamonds. In this case, light enters the diamond with such an inclination that the rays are reflected inside the glass, bouncing the rays against the inner faces.
Sometimes we can see a fuzzy circle around the sun. This is caused by the reflection of sunlight on the surface of water droplets floating in the atmosphere.
What is the refraction of light?
The refraction of light occurs when light passes from one medium to another. It is the phenomenon that explains why a straight object is bent when we put it in water. The ray of light is deflected by moving to a different medium than it is.
Refraction of light occurs on the separating surface of media of different density such as air and water, or air and glass, which affects the speed of light propagation. The deviation of the propagation direction will be larger as well as the difference in the propagation speed in the two media.
In the refraction of light, the incident ray and the refracted ray are distinguished. The angle of incidence is formed between the incident ray and the normal line. Whereas between the refracted and the normal ray the angle of refraction is formed.
Each medium has one refractive index (n) which is the relationship between the speed of light propagation in a vacuum (c) and the speed of light propagation in this medium (v):
n = c / v
The refractive index is inversely proportional to the speed of light in the medium; that is, the higher the refractive index the lower the propagation rate, and vice versa. Thus, for glass, water and plastic is greater than 1; it has no units, as it is a relationship between velocities.
The refraction of light can occur simultaneously with reflection. For example, if light strikes a face of a block of glass, it is reflected and refracted at the glass-air boundary.
Laws of refraction (Snell-Descartes law)
The laws of refraction explain how this phenomenon occurs. It was the physicist and mathematician Christiaan Huygens who deduced these laws which are summarized in:
- First law: the incident ray on the separation surface of two media, the normal on the surface at the point of incidence and the refracted ray are in the same plane.
- Second law: refractive indices n1 in2the angle of incidence α1 and the angle of refraction α2 are related by the following expression:
n1. sin (α2 ) = n2. sin (α2)
When the light strikes perpendicularly (angle of incidence equal to 0) there is no deflection of the light, that is, the incident ray follows its linear trajectory.
Examples of light refraction
The refraction of light explains many of the phenomena we encounter in our daily lives. Let’s look at some examples.
The discontinuous straw
When a straight object, such as a pencil or a straw, is inserted into a glass of water or other liquid, it appears to fail.
Double image in water tanks
Water has a different refractive index than air. Therefore, when we see objects or beings inside an aquarium, we can see more than one image.
The refractive index of a substance is used to indicate the concentration of some compounds. This is why an instrument called a refractometer is used, where a few drops of the solution are placed on a prismatic surface, and the angle of refraction is measured.
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