Raindrop Elevation & Colour

$0.00

Clear

Description

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

Raindrop Elevation & Colour

Look carefully at the diagram at the top of the page. Now check out the following questions (and answers)!

  1. Does light undergo refraction as it enters a raindrop?
  2. Does light undergo dispersion as it enters a raindrop?
  3. Are rainbow colours spectral colours?
  4. What happens when light undergoes refraction?
  5. Is magenta a spectral colour?

About the diagram

Introducing the diagram! Read back and forward between the image at the top of the page and the explanation below!

About the diagram
  • This diagram deals with how a single raindrop can contribute to the formation of a primary rainbow.
  • The diagram shows that a single falling raindrop appears red then orange, yellow, green, blue and finally violet as it falls towards the ground.
  • It is the elevation of a droplet relative to the rainbow axis and observer that determines its colour at any moment as it falls.
  • Notice that the diagram shows a ray of white light entering the top half of the raindrop and reflecting once off the interior surface before exiting towards the observer. This is always the case if a raindrop is part of a primary bow.
  • So this is the sequence:
    • At its largest angular distance from the axis, a raindrop appears red to an observer as it enters into the outer edge of the primary bow.
    • Moments later, as that same raindrop falls, and its angular distance decreases, it changes colour, first from red and finally to violet. The diagram shows the moments at which it appears red, yellow and blue.
    • As it falls further and its angular distance reduces below 40.70 it exits the inside edge of the bow.
    • The droplet is now almost invisible but continues to contribute a little to a scattering of white light that fills this area within the arcs with a light glow.
Overview of raindrops

An idealized raindrop forms a sphere. These are the ones that are favoured when drawing diagrams of both raindrops and rainbows because they suggest that when light, air and water droplets interact they produce predictable and replicable outcomes.

  • In real-life, full-size raindrops don’t form perfect spheres because they are composed of water which is fluid and held together solely by surface tension.
  • In normal atmospheric conditions, the air a raindrop moves through is itself in constant motion, and, even at a cubic metre scale or smaller, is composed of areas at slightly different temperatures and pressure.
  • As a result of turbulence, a raindrop is rarely in free-fall because it is buffeted by the air around it, accelerating or slowing as conditions change from moment to moment.
  • The more spherical raindrops are, the better defined is the rainbow they produce because each droplet affects incoming sunlight in a consistent way. The result is stronger colours and more defined arcs.
Real-life raindrops
  • Raindrops start to form high in the atmosphere around tiny particles called condensation nuclei — these can be composed of particles of dust and smoke or fragments of airborne salt left over when seawater evaporates.
  • Raindrops form around condensation nuclei as water vapour cools producing clouds of microscopic droplets each of which is held together by surface tension and starts off roughly spherical.
  • Surface tension is the tendency of liquids to shrink to the minimum surface area possible as their molecules cohere to one another.
  • At water-air interfaces, the surface tension that holds water molecules together results from the fact that they are attracted to one another rather than to the nitrogen, oxygen, argon or carbon dioxide molecules also present in the atmosphere.
  • As clouds of water droplets begin to form, they are between 0.0001 and 0.005 centimetres in diameter.
  • As soon as droplets form they start to collide with one another. As larger droplets bump into other smaller droplets they increase in size — this is called coalescence.
  • Once droplets are big and heavy enough they begin to fall and continue to grow. Droplets can be thought to be raindrops once they reach 0.5mm in diameter.
  • Sometimes, gusts of wind (updraughts) force raindrops back into the clouds and coalescence starts over.
  • As full-size raindrops fall they lose some of their roundness, the bottom flattens out because of wind resistance whilst the top remains rounded.
  • Large raindrops are the least stable, so once a raindrop is over 4 millimetres it may break apart to form smaller more regularly shaped drops.
  • In general terms, raindrops are different sizes for two primary reasons,  initial differences in particle (condensation nuclei) size and different rates of coalescence.
  • As raindrops near the ground, the biggest are the ones that bump into and coalesce with the most neighbours.

Some key terms

Move to the next level! Check out the following terms.

Colour

Things appear coloured to an observer because colour corresponds with a property of light that is visible to the human ...
Read More

Dispersion

Dispersion (or chromatic dispersion) refers to the way that light, under certain conditions, separates into its component wavelengths and the ...
Read More

Internal reflection

Internal reflection takes place when light travelling through a medium such as water fails to cross the boundary into another ...
Read More

Observer

A human observer is a person who engages in observation by watching things. In the presence of visible light, an ...
Read More

Reflection

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

Refraction

Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the interface between ...
Read More

Spectral colour

A spectral colour is a colour evoked in normal human vision by a single wavelength of visible light, or by ...
Read More

White light

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities ...
Read More

All images are free to download

Download diagrams: Slides


All our DIAGRAMS are available for download as slides and we are working on creating illustrations.

All slides share common specifications:

  • Titles: Slides have titles.
  • Backgrounds: Black.
  • Size: 1686 x 1124 pixels (3:2 aspect ratio).
  • Slides are available in two file formats: JPG, AI (Adobe Illustrator).

Our Slides are optimized for viewing on-screen.
Our Illustrations are optimized for printing on A4 pages in portrait format.

Download diagrams: Illustrations


All our DIAGRAMS are available for download as slides and we are working on creating illustrations.

All illustrations share common specifications:

  • 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.
  • All Illustrations are available in two file formats: JPG, AI (Adobe Illustrator).

Our Illustrations are optimized for printing on A4 pages in portrait format.
Our Slides are optimized for viewing on-screen.

Download agreement

Download Agreement


Before downloading or cutting and pasting from lightcolourvision.org we ask you to agree to the following terms:

  1. All information, images and other assets displayed or 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 how the material can be used.
  4. Please contact ric.lightcolourvision@gmail.com before considering any use not covered by the terms of the agreement above.

If you are a student, educator or researcher you might also like to read our posts Copyright: Credit where credit’s due and Citation and bibliographies before copying and pasting material into essays, assignments or other academic work. They include advice on avoiding plagiarism and how to credit other people’s words, images and assets before submitting your work for marking or assessment. If you are confused, just ask a friendly teacher, librarian, or other member of academic staff.

File types: JPG


Download the image on this page as a JPG file:

  • All JPG images available for download are 1686 x 1124 pixels (3:2 aspect ratio).
  • Text on JPG images with white backgrounds is styled as Calibri 24pt Italic.
  • If the image you need is not exactly what you want, download it as an AI (Adobe Illustrator) file and edit it.
  • All the images in our RESOURCE LIBRARY were created in Adobe Illustrator AS vector drawings.

Did you know:

  • JPG stands for Joint Photographic Experts Group who created the standard.
  • The JPG file extension is used interchangeably with JPEG.
  • JPG files can be compressed for use on websites.
  • JPG files can be placed or pasted directly into MS Office documents.

File types: AI


Download the image on this page as an AI (Adobe Illustrator) file:

  • All .AI images available for download are 1686 x 1124 pixels (3:2 aspect ratio).
  • All the images in our RESOURCE LIBRARY were created in Adobe Illustrator AS vector drawings.
  • Vector drawing can be scaled up or down without any loss of quality.

Did you know:

  • AIl .AI (Adobe Illustrator) files downloaded from this website can be re-edited using Adobe Illustrator for your own personal use.
  • You can 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 for all written material on this website.

Cut and copy text

If you are cutting/copying text please do a spell-check to make sure the material matches the spelling in your own document.

Downloading diagrams

The original versions of all our diagrams use English (UK) spelling.

  • Download .AI (Adobe Illustrator) versions of diagrams to change the spelling or language used for titles, labels etc.
  • When downloading .JPG versions, look out for .JPG (UK) or .JPG (US) in the download dialogue box.
  • We are adding American English (US) versions of diagrams on request. Just contact us and let us know what you need.
  • Read our Download Agreement during the download process for information on Copyright.
  • Please contact us if you can help us to produce diagrams in other languages.

Find out more


Like to know more?

Please contact kiaora.lightcolourvision@gmail.com if you have questions about any aspect of this project.