Refraction & Dispersion of White Light

$0.00

The diagram illustrates chromatic dispersion:


Description

Refraction & Dispersion of White Light

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
Refraction refers to the way light changes both direction and speed as it travels from one transparent medium into another.
Yes! Light separates into different colours during the course of refraction.
Yes! Refraction occurs as light crosses the boundary between transparent media with different refractive indices.
Yes! Light travels faster in air than in either glass or water.

About the diagram

Overview of this page

An overview of refraction

  • Refraction refers to the way that light (electromagnetic radiation) changes speed and direction 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.
  • Refraction is the result of the differences in the optical density of transparent media. Gases have a very low optical density whilst diamonds have a high optical density.
  • 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 reflection.
  • As light travels across the interface between different media it changes speed.
  • Depending on the media through which light is refracted, its speed can either increase or decrease.

An overview of 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 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 spectral colours – ROYGBV.
  • 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.
  • 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.

An overview of refraction and wavelength

  • 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 new 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.

The diagram

The diagram shows an incident ray of white light approaching the boundary between air and glass.

  • As the ray crosses the boundary into the glass it bends towards the normal (the dotted green line).
  • Refraction is towards the normal because the ray travels from air, the faster, less optically dense medium with a smaller refractive index into the glass, a slower, more optically dense medium with a higher refractive index.

A familiar example of dispersion is when white light strikes a prism and a rainbow of colours become visible to an observer.

  • As light enters a prism it separates into its component wavelengths which an observer perceives as bands of colour.
  • Colour is not a property of electromagnetic radiation, but a feature of visual perception experienced by an observer in the presence of different wavelengths of light.

Remember:

  • In the right conditions, all transparent media cause incident light to change direction and to disperse into their component colours.
  • When light is refracted and changes direction, the angle is determined by the refractive index of the medium it enters.
  • Refractive index (n) is equal to the speed of light in a vacuum (c) divided by the speed of light in the medium (v)
  • Light travels at 299.792 kilometres per second in a vacuum.
  • Only a narrow range of wavelengths that form the full electromagnetic spectrum are visible to the human eye.
  • The wavelengths that we can see are known as the visible spectrum.
  • The presence of different wavelengths of light around us results in the colours we see in the world.

Refractive index

  • The refractive index (also known as the index of refraction) of a transparent medium allows the path of refracted light through a transparent medium to be calculated.
  • The refractive index is a ratio calculated by dividing the change in the speed of light in a vacuum by its speed as it travels through a specific medium.
  • The refractive index of a medium can be calculated using the formula:

n = refractive index, c = speed of light in a vacuum, v = speed of light in a transparent medium

  • When light travels through a vacuum, such as outer space, it travels at its maximum speed of 299,792 kilometres per second.
  • When light travels through any other transparent medium it travels more slowly.
  • Refractive indices describe the ratio between the speed of light in a vacuum and the speed of light in another medium.
  • Most transparent media have a refractive index of between 1.0 and 2.0.
  • Whilst the refractive index of a vacuum has the value of 1.0, the refractive index of water is 1.333.
  • The ratio between them is therefore 1:1.333
  • A simple example of a ratio is of mixing concrete using 1 part of cement to 2 part of sand. The ratio is expressed as 1:2.
  • If we divide the refractive index for light travelling through a vacuum (1.0) by the refractive index for glass (1.333) we find that light travels at 75% of the speed of light in a vacuum.

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.

Some key terms

In physics and optics, a medium refers to any material (plural: media) through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.

  • Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
  • The properties of the medium, such as its density and composition, influence how light propagates through it.
  • Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
  • Examples of Mediums:
    • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
    • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
    • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.
  • The permittivity (electrical response) and permeability (magnetic response) of a medium determine how light interacts with it. These properties influence factors like:
    • Refraction: Bending of light as it travels from one medium to another with different densities.
    • Reflection: Bouncing back of light when it encounters a boundary between mediums.
    • Absorption: Light being captured and converted into other forms of energy (like heat) by the medium.
  • In physics and optics, a medium refers to any material through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.
  • Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
  • The properties of the medium, such as its density and composition, influence how light propagates through it.
  • Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
  • Examples of Mediums:
    • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
    • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
    • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.

The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time.

Reflection takes place when incoming light strikes the surface of a medium, obstructing some wavelengths which bounce back into the medium from which they originated.

Reflection takes place when light is neither absorbed by an opaque medium nor transmitted through a transparent medium.

If the reflecting surface is very smooth, the reflected light is called specular or regular reflection.

Specular reflection occurs when light waves reflect off a smooth surface such as a mirror. The arrangement of the waves remains the same and an image of objects that the light has already encountered become visible to an observer.

Diffuse reflection takes place when light reflects off a rough surface. In this case, scattering takes place and waves are reflected randomly in all directions and so no image is produced.

Optical density is a measurement of the degree to which a refractive medium slows the transmission of light.

  • The optical density of a medium is not the same as its physical density.
  • The more optically dense a medium, the slower light travels through it.
  • The less optically dense (or rare) a material is, the faster light travels through it.
  • A vacuum has the least optical density and so light travels through it at a maximum speed of 299,792 kilometres per second.
  • Optical density accounts for the variation in refractive indices of different media.

https://en.wikipedia.org/wiki/Absorbance

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of the wave.

The angle of refraction measures the angle to which light bends as it crosses the boundary between different media.

  • The angle of refraction is measured between the bent ray and an imaginary line called the normal.
  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • Snell’s law is a formula used to describe the relationship between the angle of incidence and the angle of refraction when light crosses the boundary between transparent media, such as water and air or water and glass.

In physics and optics, a wave diagram uses a set of drawing conventions and labels to describe the attributes of light waves including wavelength, frequency, amplitude and direction of travel.

The angle of incidence measures the angle at which incoming light strikes a surface.

  • When light is travelling towards something it is said to be incident to that surface or object.
  • The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
  • Incident light may have travelled from the Sun or a man-made source or may have already been reflected off another surface such as a mirror.
  • When incident light strikes a surface or object it may undergo absorption, reflection, refraction, transmission or any combination of these optical effects.
  • The angle of incidence measures the angle at which incoming light strikes a surface.
  • The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
  • See this diagram for an explanation: Reflection of a ray of light
  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • If the boundary between the media is curved, then the normal is drawn at a tangent to the boundary.

The angle of incidence refers to the angle at which incoming light strikes a surface and is measured between a ray of incoming light and an imaginary line called the normal.

  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • The angle at which incident light from the Sun or a light bulb strikes a surface can affect the outcome. For instance, when incident light hits a mirror, the angle of incidence determines the angle of reflection.

Diagrams are free to download

Downloads: Slides or Illustrations


DOWNLOAD DIAGRAMS
  • SLIDES are optimized for viewing on-screen.
  • ILLUSTRATIONS are optimized for printing on A4 pages in portrait format.
SLIDES
  • Slides are available in JPG and AI (Adobe Illustrator) file formats.
  • Titles: Slides have titles.
  • Backgrounds: Black.
  • Size: 1686 x 1124 pixels (3:2 aspect ratio).
ILLUSTRATIONS
  • Illustrations are available in JPG and AI two file formats.
  • Titles: No titles.
  • Backgrounds: White.
  • Size: 1686 x 1124 (3:2 aspect ratio). So all illustrations reproduce at the same scale when inserted into Word documents etc.
  • Labels: Calibri 24pt Italic.

File formats: JPG & AI


DOWNLOAD THE DIAGRAM ON THIS PAGE AS A JPG FILE
  • JPG (JPEG) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
  • If a JPG diagram doesn’t fit your needs, you can download it as an AI (Adobe Illustrator) file and edit it yourself.
  • JPG files can be placed or pasted directly into MS Office documents.
DOWNLOAD THE DIAGRAM ON THIS PAGE AS AN AI file
  • All AI (Adobe Illustrator) diagrams are 1686 x 1124 pixels (3:2 aspect ratio).
  • All our diagrams are created in Adobe Illustrator as vector drawings.
  • Save as or export AI files to other formats including PDF (.pdf), PNG (.png), JPG (.jpeg) and SVG(.svg) etc.

Spelling: UK & US


We use English (UK) spelling by default here at lightcolourvision.org.

COPY & PASTING TEXT
  • After copy/pasting text please do a spell-check to change our spelling to match your own document.
DOWNLOAD DIAGRAMS
  • Download AI versions of diagrams to change the spelling or language used for titles, labels etc.
  • We are adding American English (US) versions of diagrams on request. Just contact us and let us know what you need.
  • When downloading JPG versions of diagrams, look out for JPG (UK) or JPG (US) in the download dialogue box.

Download agreement


DOWNLOAD AGREEMENT

Light, Colour, Vision & How To See More (https://lightcolourvision.org) : Copyright © 2015-2022 : MediaStudies Trust.

Unless stated otherwise the author of all images and written content on lightcolourvision.org is Ric Mann.

ALL RIGHTS RESERVED

No part of this website may be copied, displayed, extracted, reproduced, utilised, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical or otherwise including but not limited to photocopying, recording, or scanning without the prior written permission of MediaStudies Trust.

EXCEPTIONS

Exceptions to the above statement are made for personal, educational and non-profit purposes:

Before downloading, cutting and pasting or reproducing any information, images or other assets found on lightcolourvision.org we ask you to agree to the following terms:

  1. All information, images and other assets displayed and made available for download on the lightcolourvision.org website are copyright. This means there are limitations on how they can be used.
  2. All information, images and other assets displayed or made available for download are solely and exclusively to be used for personal, educational and non-profit purposes.
  3. When you find the resources you need, then part of the download process involves you (the user) ticking a box to let us (at lightcolourvision.org) know we both agree on how the material can be used.
  4. Please contact [email protected] before considering any use not covered by the terms of the agreement above.

The copyright to all information, images and all other assets (unless otherwise stated) belongs to:

The Trustees. MediaStudies Trust
111 Lynbrooke Avenue
Blockhouse Bay
Auckland 0600
New Zealand
[email protected]

We love feedback

Your name and email address will be used solely to provide you with information you have specifically requested. See our privacy policy at https://lightcolourvision.org/privacy/.


We welcome your feedback 🙂









    Note: The feedback form records the URL of the current page


    Thank you so much for your time and effort