Reflection and refraction of light

Reflection and refraction of light are two physical phenomena that a ray of light can experience. In reflection, the light ray bounces off a surface, while in refraction the light ray that passes from one medium to another changes its angle of propagation.

Reflection of lightRefraction of light
DefinitionOptical phenomenon where the light beam bounces when it meets a material.Optical phenomenon where the light beam changes direction when passing through a medium of different density.
Components (edit)Incident
ray Reflected ray
Reflective surface
Normal line
Angle of incidence
Angle of reflection
ray Refracted ray
Surface between media
Normal line
Angle of incidence
Angle of refraction
HalfIt occurs in the same mediumIt occurs on the border between two media of different density
  • The normal and the incident and reflected rays are in the same plane
  • Angle of incidence = angle of reflection
  • The normal and the incident and refracted rays are in the same plane
  • The refractive index of medium 1 times the sine of the angle of incidence is equal to the refractive index of medium 2 times the sine of the refractive angle:

1 . you (α 2 ) =n 2 . you (α 2 )

  • The speed of light propagation does not change
  • The frequency of the light wave does not change
  • The intensity of the reflected beam is lower
  • The speed of the propagation of light changes.
  • It depends on the refractive index of the medium.
Solar oven
Gem shine
Solar halo
Double image in aquariums
Discontinuous straw

What is light reflection?

The reflection of light is the phenomenon that occurs when we have the sensation that a ray of light is bouncing off a surface.
What actually happens is that the light beam is returned when it collides with a medium other than the one it is traveling, as would happen when a ball is kicked against a wall.

In the reflection of light you can distinguish the original ray or incident ray and the ray that is returned or reflected ray . At the point where the incident and reflected rays meet, an imaginary line is drawn perpendicular to the surface, known as the normal .

Between the incident ray and the normal the angle of incidence is formed, and between the normal and the reflected ray the angle of reflection is formed. Thus, the direction in which the 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 the same in 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 light ray when it is returned. 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 equal to 30 ° C, the angle of reflection is equal to 30 ° C. If the light is incident perpendicularly, the angle of incidence and the angle of reflection are equal to 0 ° C, so the light will be reflected reversing the direction of propagation.

Examples of light reflection

Reflection of light occurs in nature in many situations and with various applications.

Solar Furnace

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 French National Center for Scientific Research built a solar furnace in Odeillo to study the properties of materials in high solar temperature environments. This oven is based on the concentration of solar rays by reflection, reaching 1000 kilowatts per square meter.

Mirror imaging

A mirror is a smooth surface where light beams bounce off and an image is formed by the reflection of light. 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 varied 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, the light enters the diamond at such an inclination that the rays are reflected inside the crystal, bouncing the rays against the internal faces.

hello solar

Sometimes we can see a diffuse circle that surrounds the sun. This is produced 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 looks bent when we put it in water. The ray of light is deflected when passing to a different medium than the one it came from.

The refraction of light occurs at the separation surface of media of different density such as air and water, or air and glass, which affects the speed of propagation of light. The deviation of the propagation direction will be greater the greater 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. While between the refracted ray and the normal, the angle of refraction is formed.

Each medium has an index of refraction ( n ) which is the relationship between the speed of propagation of light in a vacuum (c) and the speed of propagation of light in that medium (v):

= 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 speed of propagation, and vice versa. Thus, for glass, water and plastic it is greater than 1; it has no units, since it is a relationship between speeds.

Refraction of light can occur simultaneously with reflection. For example, if light falls on one face of a glass block, 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 that are summarized in:

  • First law : the incident ray on the separation surface of two media, the normal to the surface at the point of incidence and the refracted ray are in the same plane.
  • Second law : the refractive indices n 1 and n 2 , the angle of incidence α 1 and the angle of refraction α 2 are related by the following expression:

1 . you (α 2 ) =n 2 . you (α 2 )

When the light is incident perpendicularly (angle of incidence equal to 0) there is no deflection of the light, that is, the incident ray follows its linear path.

Examples of the refraction of light

The refraction of light explains many of the phenomena we encounter in our day to day life. Let’s look at some examples.

The discontinuous straw

When a straight object, such as a pencil or straw, is inserted into a glass of water or other liquid, it appears to break.

Double image in water tanks

Water has a different refractive index than air. So 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. For this, 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.

You may also be interested in natural phenomena .

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