# Chromatic Dispersion in a Prism

\$0.00

In this diagram a ray of incident light strikes one of the three rectangular surfaces at an angle so that it exits from the middle of another.

• The light source used produces white light which is focused into a narrow beam.
• As the ray enters the prism the angles of incidence and refraction are the same.
• When the light exits the prism the angles of incidence and refraction are the same.
SKU: N/A Category:

## Description

#### Chromatic Dispersion in a Prism

###### TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
Every wavelength of light is affected to a different degree by the refractive index of a material and as a result changes direction by a different amount when passing from one medium (such as air) to another (such as glass or water).
Yes! Light separates into different colours during the course of refraction.
Chromatic dispersion refers to the way that light separates into its component wavelengths (and so colours), under certain conditions.
Yes! Every wavelength of light is affected to a different degree by the refractive index of a transparent medium and as a result, changes direction by a different amount when passing from air to glass or glass to air.
Yes! Chromatic dispersion takes place as light crosses the boundary between one transparent medium and another if it has a different refractive index.

Have you already checked out An Introduction to Reflection, Refraction and Dispersion?

It is the opening page of our Reflection, Refraction and Dispersion Series and contains masses of useful information. This is the table of contents:

Overview

Let’s start off by reviewing what the terms refraction and dispersion refer to and sort out exactly what a prism is.

Refraction

• When light crosses the boundary between two different transparent media it undergoes refraction.
• The effect of refraction is that light changes speed and its direction of travel.
• The change in speed can be calculated if the refractive index is known.
• The index of refraction can be calculated if the speed of light in a vacuum and the speed of light in the medium is known.
• The refractive index of a medium is calculated using the formula: Where n = refractive index, c = speed of light in a vacuum, v = speed of light in a transparent medium.
• The amount that the path of a ray of light bends when it changes direction is calculated using the Law of refraction (also known as Snell’s law).

Chromatic dispersion

Chromatic dispersion is often simply called dispersion.

• Whenever you see a rainbow of colours in a patch of oil, in the edge of a sheet of glass or a crystal, it is caused by dispersion.
• White light, containing all wavelengths of the visible spectrum, disperses into a rainbow of colours.
• Dispersion takes place because the refractive index of any transparent medium is different for each wavelength of light.
• The diagram at the top of the page shows that in certain circumstances when white light strikes a prism, a rainbow of colours become visible to an observer.

Prism

In the field of optics, a prism is made of glass or other transparent material with flat, polished surfaces.

• Prisms are generally made from crown or flint glass depending on their intended use.
• Flint glass prisms are often used for experimental purposes to study the refraction and dispersion of light.
• A triangular prism consists of two triangular ends and three rectangular faces.
• If white light is to be refracted or dispersed by a prism into its component colours a narrow beam is pointed towards one of the rectangular faces.
• Dispersive prisms are used to break up light into its constituent spectral colours.
• Reflective prisms are used to reflect light, in order to flip or invert a light beam.
• Triangular reflective prisms are a common component of cameras, binoculars and microscopes.

Crown glass

Crown glass is a type of optical glass made without lead or iron and used in the manufacture of lenses and other tools and equipment concerned with the visible part of the electromagnetic spectrum.

• Crown glass produces low levels of chromatic dispersion which is of particular concern in the manufacture of lenses.
• Dispersion is unavoidable but a well-designed lens is able to reorganize light so that, in the end, all wavelengths converge at the same point and so produce a sharp image with a high degree of colour accuracy.

Flint glass

Flint glass is made from a combination of silicon dioxide (SiO2) and lead or potassium.

• Flint glass typically has a higher refractive index value than crown glass which means that dispersion is more evident.
• Flint glass absorbs most ultraviolet light but comparatively little visible light and is often used in telescope lenses.

The diagram

In this diagram a ray of incident light strikes one of the three rectangular surfaces at an angle so that it exits from the middle of another.

• The light source used produces white light which is focused into a narrow beam.
• As the ray enters the prism the angles of incidence and refraction are the same.
• When the light exits the prism the angles of incidence and refraction are the same.
• The light source and prism are arranged on a suitable surface, such as a piece of paper so that the dispersed colours are visible to an observer.
• Remember that light is only visible when either its source is in view or when transmitted light strikes a surface, in this case, the paper.
• The human eye sees white when all the colours that make up visible light are combined together and strike a neutral coloured surface that reflects all wavelengths equally.

Remember that:

• The incident white light is refracted towards the normal as it enters the prism because the optic density of glass is greater than air.
• On entry to the prism, a small amount of dispersion takes place.
• As the dispersed colours exit the prism they are refracted away from the normal because the optic density of air is less than air.
• On exiting the prism, the amount of dispersion of each colour is more pronounced.
• The amount that light bends as refraction and dispersion take place depends on:
• The type of glass.
• The composition of wavelengths produced by the light source.
• The angle of incidence of the light.
• The refractive index of the glass for each wavelength.

#### Some key terms

An additive colour model explains how different coloured lights (such as LEDs or beams of light) are mixed to produce other colours.

• Additive colour refers to the methods used and effects produced by combining or mixing different wavelengths of light.
• The RGB colour model and HSB colour model are examples of additive colour models.
• Additive colour models such as the RGB colour model and HSB colour model can produce vast ranges of colours by combining red, green, and blue lights in varying proportions.
• An additive approach to colour is used to achieve precise control over the appearance of colours on digital screens of TVs, computers, and phones.

Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the interface between one transparent medium and another.

• As light travels from a fast medium such as air to a slow medium such as water it bends toward the normal and slows down.
• As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from the normal and speeds up.
• In a diagram illustrating optical phenomena like refraction or reflection, the normal is a line drawn at right angles to the boundary between two media.
• A fast (optically rare) medium is one that obstructs light less than a slow medium.
• A slow (optically dense) medium is one that obstructs light more than a fast medium.
• The speed at which light travels through a given medium is expressed by its index of refraction.
• If we want to know in which direction light will bend at the boundary between transparent media we need to know:
• Which is the faster, less optically dense (rare) medium with a smaller refractive index?
• Which is the slower, more optically dense medium with the higher refractive index?
• The amount that refraction causes light to change direction, and its path to bend, is dealt with by Snell’s law.
• Snell’s law considers the relationship between the angle of incidence, the angle of refraction and the refractive indices (plural of index) of the media on both sides of the boundary. If three of the four variables are known, then Snell’s law can calculate the fourth.

The perception of colour by an observer results from properties of light that are visible to the human eye. The visual experience of colour is associated with terms like red, blue and yellow.

• The observation of colour depends on:
• The range and intensity of wavelengths of visible light emitted by a light source, and the various media and materials it encounters on its journey to the retina of a human eye
• Optical phenomena such as absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission.
• Predispositions of an observer, such as their personal and social experience, health and state of mind.
• A light source is a natural or man-made object that emits one or more wavelengths of light.
• Natural light sources include:
• The Sun is the most important natural light source in our lives and emits every wavelength of light in the visible spectrum.
• Celestial sources of light include other stars, comets and meteors.
• Other natural sources of light include lightning, volcanoes and forest fires.
• There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
• Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps
• Tungsten lights: These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
• Halogen bulbs: These are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
• Fluorescent lights: These are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. Fluorescent lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
• LED lights: An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor. An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.
• Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.

An observer perceives bands of colour when visible light separates into its component wavelengths and the human eye distinguishes between different colours.

• The human eye and brain together translate light into colour.
• When sunlight is dispersed by rain and forms a rainbow, an observer will typically distinguish red, orange, yellow, green, blue and violet bands of colour.
• Although a rainbow contains electromagnetic waves with all possible wavelengths between red and violet, some ranges of wavelengths appear more intense to a human observer than others.

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

• The angle of refraction is measured between a ray of 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.
• See this diagram for an explanation: Refraction of a ray of light
• If the boundary between the media is curved, the normal is drawn perpendicular to the boundary.

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

As light crosses the boundary between two transparent media, the law of refraction (Snell’s law) states the relationship between the angle of incidence and angle of refraction of the light with reference to the refractive indices of both media as follows:

When electromagnetic radiation (light) of a specific frequency crosses the interface of any given pair of media, the ratio of the sines of the angles of incidence and the sines of the angles of refraction is a constant in every case.

• Snell’s law deals with the fact that for an incident ray approaching the boundary of two media, the sine of the angle of incidence multiplied by the index of refraction of the first medium is equal to the sine of the angle of refraction multiplied by the index of refraction of the second medium.
• Snell’s law deals with the fact that the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes across the boundary from one medium to another.
• Snell’s law can be used to calculate the angle of incidence or refraction associated with the use of lenses, prisms and other everyday materials.
• When using Snell’s law:
• The angles of incidence and refraction are measured between the direction of a ray of light and the normal – where the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
• The wavelength of the incident light is accounted for.
• The refractive indices used are selected for the pair of media concerned.
• The speed of light is expressed in metres per second (m/s).

Visible light is the range of wavelengths of electromagnetic radiation perceived as colour by human observers.

• Visible light is a form of electromagnetic radiation.
• Other forms of electromagnetic radiation include radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
• Visible light is perceived by a human observer as all the spectral colours between red and violet plus all other colours that result from combining wavelengths together in different proportions.
• A spectral colour is produced by a single wavelength of light.
• The complete range of colours that can be perceived by a human observer is called the visible spectrum.
• The range of wavelengths that produce visible light is a very small part of the electromagnetic spectrum.

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 wavelength of an electromagnetic wave is measured in metres.
• Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves,  forms a band of wavelengths on the electromagnetic spectrum.
• The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
• Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
• The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.

• 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

• 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.
• 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 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.

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.

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