Introduction to Reflection, Refraction and Dispersion

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An Introduction to Reflection, Refraction and Dispersion

Here are all the diagrams in our Introduction to Reflection, Refraction and Dispersion series

Each one appears on its own page with a full explanation.
AND
Did you know that all our diagrams are FREE to download!

Reflection of a Ray of White Light
Refraction-of-a-Ray-of-White-Light-Towards-the-Normal-80 / 06900-0-A-BL-EN
Refraction of Light Towards the Normal
Refraction of a Ray of White Light Away from the Normal
Reflection and Refraction of a Ray of White Light
Reflection and Refraction at a Curved Boundary
Reflection and Refraction Parallel to the Normal
Reflection and Refraction Parallel to the Normal at a Curved Boundary
Refraction of a Ray of Red Light in Detail
Chromatic Dispersion of a Ray of White Light
Chromatic Dispersion of Red Green and Blue Wavelengths
Refraction and Dispersion of a Ray of White Light
Refraction and Dispersion of Wavelengths of Light
Refractive Index Explained
How to Use the Refractive Index of a Medium
The Law of Refraction Explained
Refraction of Light Away from the Normal
Prism Splits a Ray of Light into Spectral Colours 06700-0-A-BL-EN
Sunlight-reflects-off-a-Fish-in-Water-80 / 07050-0-A-BL-EN
Refraction-Reflection-and-Total-Internal-Reflection-80 / 07100-0-A-BL-EN
Actual and Observed Position of an Object in Water
Refraction-of-Red-Green-and-Blue-Rays-in-a-Raindrop 07200-0-A-BL-EN

To find out more about the diagrams above . . . . read on!

About the Diagrams

There are over two dozen pages in this section so far, and every one features a diagram and full explanation

Choose a page by clicking on an image above.

But don’t forget about the information below. Here is a list of the sections on this page.

Introducing reflection

Types of reflection

Introducing refraction

Calculating the angle of refraction

Introducing chromatic dispersion

Introducing refraction and wavelength

Introducing reflection

  • Reflection takes place when incoming light strikes the surface of a medium and the light bounces off and returns into the medium from which it originated.
  • Reflection is predictable and always obeys three rules (the laws of reflection):
    • The incident ray, the reflected ray and the normal all lie in the same plane.
    • The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes with the normal.
    • The reflected ray and the incident ray always appear on opposite sides of the normal.
  • Reflection takes place when light is neither absorbed by an opaque medium nor transmitted through a transparent medium.

Types of reflection

  • When sunlight strikes window glass, some light is reflected and some is transmitted through the glass into the room beyond.
  • The type of glass made for picture framing is designed to reflect some wavelengths and to transmit others.
  • When light illuminates objects and then goes on to strike a mirror, the reflected image can be seen by an observer.
  • A reflected image contains objects that we recognise and is made up of visible wavelengths of light and their corresponding colours.
  • If a reflecting surface is very smooth, light waves remain in the same order as they bounce off the surface, producing a specular reflection.
  • A diffuse reflection, in which no image is visible, results from light reflecting off a rough surface and light waves scattering in all directions.
  • Reflection is independent of the optical density of the medium through which incident light travels or of the medium it bounces off.

Introducing refraction

  • Refraction refers to the way that light (electromagnetic radiation) changes direction and speed as it travels from one transparent medium into another.
  • Refraction takes place as light travels across the boundary between different transparent media and is a result of their different optical properties.
  • As light travels across the interface between different media (such as between air and glass) it changes speed.
  • Depending on the media through which light is refracted, its speed can increase or decrease.
  • When light is refracted its path bends and so changes direction.
  • The effect of refraction on the path of a ray of light is measured by the difference between the angle of incidence and the angle of refraction.

Remember that:

  • As the speed of light changes so does its wavelength but the frequency and so the colour an observer sees remains the same.
  • The result of the change in direction is that rays either bend towards or away from the normal.
  • The normal is an imaginary line drawn on a ray diagram at right angles (perpendicular) to the boundary between two media.
  • The change between the angle of incidence and the angle of refraction of a ray of light is always measured between the ray and the normal.
  • Whether light bends towards or away from the normal depends on the difference in optical density of the new medium it encounters.
  • An incident ray of light is refracted towards the normal and slows down when it travels from air into glass. Compared with air, glass is a slower, more optically dense medium (with the higher refractive index).
  • An incident ray of light is refracted away from the normal and speeds up when it travels from glass into air. Compared with glass, air is a faster, less optically dense medium (with a lower refractive index).

For an explanation of the refractive index (index of refraction) of a medium see: Refractive Index Explained.

For an explanation of how to use the refractive index of a medium see: How to Use the Refractive Index of a Medium.

For an explanation of the Law of Refraction see: Snell’s Law of Refraction Explained.

Calculating the angle of refraction

  • The direction in which a ray bends, and the precise angle, can be calculated if the type and refractive indices of both media are known.
  • The effect of refraction can be calculated using a neat little equation called the law of refraction (also known as Snell’s law).
  • If three of the variables are known, the law of refraction can be used to calculate the fourth.
  • Tables of refractive indices are available for common materials so that the change in direction of a ray can be calculated.
  • Tables of refractive indices for common materials often provide both the refractive index for white light as well as indices for specific wavelengths.

Introducing chromatic dispersion

  • The term chromatic dispersion (often simply called dispersion) refers to the way that different wavelengths of light separate at the boundary between transparent media during the process of refraction.
  • Dispersion occurs because refraction causes every wavelength of light to alter speed, and at the same time, to bend and change direction by a different amount.
  • Dispersion causes the separate wavelengths present in a ray of light to fan out so that their corresponding colours become visible to an observer.
  • When white light is dispersed, the spread of colours has red on one side and violet at the other.
  • The colours produced by dispersion are the spectral colours – ROYGBV.
  • For dispersion to occur the incident light approaching the boundary between two different transparent media must contain a sufficiently wide range of wavelengths to enable them to separate out so that their associated colours are visible to an observer.

Introducing refraction and wavelength

  • Light slows and changes direction as it travels through a medium other than a vacuum (such as air, glass or water).
  • Every wavelength of light is affected to a different degree when it encounters a medium and undergoes refraction.
  • Every wavelength of light changes both speed and direction by a different amount when it encounters a medium and undergoes refraction.
  • The change in angle for any wavelength of light undergoing refraction within a specific transparent medium can be predicted if the refractive index of the medium is known.
  • The refractive index for a medium is calculated by finding the difference between the speed of light in a vacuum and its speed as it travels through the medium.
  • To understand dispersion we must recognise that the refractive index of a transparent medium must be corrected for different wavelengths of the visible spectrum.

More Information

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Did you know:

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