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School-college Physics Notes: Visible spectrum-colour 1.

GCSE level Physics exam revision notes on colour

Visible spectrum and colour: Part 1. Reminder - using the dispersion of light by a prism to display the 'rainbow' colours (colors) of the visible spectrum

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[KEY POINTS and learning objectives for this page, after initial notes]

INDEX of physics my notes: The visible spectrum and colour of objects

1. Reminder - using the dispersion of light by a prism to show the visible spectrum

This experiment was described on the Refraction to produce the visible light spectrum notes page.

The higher the frequency and the shorter the wavelength, the more the visible light ray is refracted.

In the 1660s the famous scientist Isaac Newton proved that white light 'contained' all the colours from violet to red.

The experiment was quite simple, having dispersed the colours with one triangular prism (left to right in the above diagram) he then used a second inverted triangular prism to recombine all the colours and reproduced the original white light (right to left on the above diagram).

That's genius for you - all you have to do is think up a really simple experiment that nobody else had though of!

If you disperse sunlight with a prism or diffraction grating, this is what the solar spectrum looks like.

The wavelengths of visible light range from ~700 nm down to ~400 nm - remember this is only one small part of the whole of the electromagnetic spectrum (EM radiation).

INDEX of my physics notes: The visible spectrum and colour of objects

Key points for COLOUR - the visible spectrum and colour

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA & CIE GCSE physics 9-1 level science examinations.

A comprehensive and exam-board-aligned summary revision guide on how to show that visible light is made up of a spectrum of different colours, tailored for GCSE/IGCSE Physics students across WJEC, CCEA, CIE, AQA, Edexcel, and OCR.

Visible Light and the Spectrum

Core Concept

White light (like sunlight) is not a single colour-it's a mixture of all the colours in the visible spectrum. This can be demonstrated using a glass prism.

Required Practical: Splitting White Light

How to Show the Spectrum

  • Apparatus: Ray box, white light source, glass prism, screen
  • Method:
    1. Shine a narrow beam of white light through a glass prism.
    2. The light refracts (bends) as it enters and exits the prism.
    3. On the screen, a spectrum of colours appears: Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV).
  • Explanation:
    • Each colour has a different wavelength.
    • Red has the longest wavelength and is refracted the least.
    • Violet has the shortest wavelength and is refracted the most.
    • This process is called dispersion.

Typical Exam Board Content

Key Points to Know
Understand refraction and dispersion; describe how a prism splits white light into a spectrum.
Explain how different wavelengths refract by different amounts; describe the visible spectrum.
Define white light as a mixture of colours; explain dispersion using a prism.
Required practical: investigate refraction and dispersion; describe the order of colours.
Know that visible light is part of the EM spectrum; explain how a prism shows the spectrum.
Describe how white light is split into colours; understand specular versus diffuse reflection.

Student Tips

  • Mnemonic: Remember the colour order with ROYGBIV.
  • Sketch it: Practice drawing a labelled diagram of light entering and exiting a prism.
  • Link it: Connect this to the electromagnetic spectrum-visible light is just one part!
  • Common Mistake: Don’t say colours are “created” by the prism-they’re separated, not made.
  • Exam Gold: Use terms like refraction, wavelength, and dispersion to score higher marks.

Real-World Examples

  • Rainbows: Natural dispersion of sunlight by water droplets.
  • CDs/DVDs: Show rainbow colours due to diffraction and interference.
  • Spectrometers: Used in science to analyse light from stars and chemicals.

Keywords, phrases and learning objectives for visible light and colour

Reminder to know using the dispersion of light by a prism you can display the 'rainbow' colours (colors) of the visible spectrum 

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INDEX of my physics notes: The visible spectrum and colour of objects

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