Refraction and reflection of light

The light rays can experience two physical phenomena: refraction and reflection. In the first, the ray of light that passes from one medium to another modifies its angle of propagation; in the second the ray of light bounces off the surface.

DefinitionRefraction occurs when light passes from one medium to another, undergoing a deviation in the same transferReflection of light occurs when the light beam bounces off the surface
ExamplesStick or straw in the water (cut or fold effect), double image in a fish tankMirror, kaleidoscope, solar halo

What is the refraction of light?

Refraction occurs when light passes from one medium to another, something that happens regularly even if we do not pay attention . It is precisely the phenomenon that explains why a straight object is bent when we introduce it to water and that many phenomenalist philosophers led him to declare that the senses were deceiving! What happens is that the rays undergo a deviation when it passes to a different medium than the one it comes from.

Then refraction occurs when there is a modification of the media where light propagates, with different densities such as air and water, air and glass, which affects the speed of propagation of light. The deviation of the direction of propagation will be greater the greater the difference in speed in the same in the two media.

In refraction, the incident and refracted rays can be distinguished. An angle of incidence is formed between the first and the normal line; while between the refracted and the normal line the angle of refraction is formed.

Of course, there are refractive indices and if there are indices we can mention a mathematizable formula. That (n) is the relationship between the speed of propagation of light in vacuum (C) and the speed of propagation of light in that medium (V): n = c / v.

The refractive index is inversely proportional to the speed of light in the medium; This means that the higher the refractive index, the lower the speed of propagation.

Laws of refraction

The laws of refraction explain how this phenomenon occurs. The physicist and mathematician Christaan ​​Huygens was the one who deduced them.

  • 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 n1 and n2, the angle of incidence α 1 and the angle of refraction α 2 are related in the following formula: 1 . sin (α  ) = n 2 . sin (α 2 ) .

An important case to clarify is that when the light falls perpendicularly, with an angle of incidence that would be 0, there is no light deviation; that is, the incident ray follows its linear path.

Examples of refraction

The refraction of light can be perceived in multiple daily phenomena. Some of them are mentioned below.

Straw in glass of water

This is a typical case of refraction and also an observable, everyday experimentation. You can see the difference between the part of the straw in the air and the part that goes into the water, giving rise to a cutting or bending effect.

The double image

The wonder of light rays: since the refraction is different in water than outside, double images can be produced (something evident in any fish tank).

What is light reflection?

The reflection of light is a phenomenon that occurs when we have the sensation that the ray of light is bouncing off the surface . What happens here is that the light ray is returned when it collides with a different moving medium.

In reflection there is a clear distinction: the original or incident ray and the returned or reflected ray. There is a point where both rays meet, drawing an imaginary line perpendicular to the surface that is known as normal.

Between the incident ray and the normal line is the angle of incidence; between the reflected ray and the normal the angle of reflection. Thus, the direction in which light is reflected depends on the shape of the reflecting surface and the direction of the incident beam.

Although light has a wave frequency and a speed that is the same in both the incident and reflected rays; however, the intensity of the reflected light is lower than the incident light.

Laws of reflection

The laws of reflection of light are those deductions that explain the propagation of the ray of light when it is returned.

  • First law:  the incident ray, the normal of 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, as shown in the drawing above, are equal. Therefore, if one angle is 30 °, the other is also 30 °. Like refraction, if light is incident perpendicularly, the angle of incidence and reflection will be equal to 0 °. The light will be reflected reversing the direction of propagation.

Reflection examples

The reflection of light also occurs in many everyday phenomena, both natural and artificial. Here are some examples of them.

hello solar

This diffuse circle around the sun, enigmatic for many, is an example of light reflection. Reflection of sunlight occurs on the surface of water droplets floating in the atmosphere.

Internal reflection

This is a reflection that can be seen in gemstones, such as diamonds. The light enters the diamond with a certain inclination, causing the rays to reflect inside the crystal: that is, they bounce off its multiple internal faces.


A kaleidoscope, very entertaining for children, is an instrument that consists of interior mirror tubes and pieces of colored glass. As it is rotated, different patterns are obtained, which is an effect of the solar reflection inside the toy itself.


And we finish the examples with one of the most massive objects that in the past had all their share of mystery, such as mirrors. These by definition is a smooth surface where the light beams bounce and an image is formed by the effect of the reflection of the light.

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