GCSE Physics What is colour? Data table of wavelengths and data table of frequencies of colours of the visible spectrum the order of the colours of the visible spectrum in terms of wavelength and frequency IGCSE/GCSE Physics revision notes

GCSE level Physics exam revision notes on colour

Visible spectrum and colour: 2. What is colour? Data table of wavelengths & frequencies for the colours of the visible spectrum

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

2. What is colour?

From our point of view, colour is what we perceive when we are looking at objects.

It represents the range of frequencies-wavelengths that the human eye can detect.

Our retina is sensitive to red, green and blue and their various proportions to make up the rest of the colours we experience.

Other animals do not necessarily see the same colours as we do.

Some animals cannot detect the full range of the visible spectrum and some can detect ultraviolet like any other colour, which we cannot.

White light is a mixture of all the different colours.

The actual colours we see, or what an instrument detects, depends on the interaction of the light on the surface of an object.

For more on the structure and function of the eye (school biology notes)

Different colours arise due to the absorption, reflection and transmission of the different wavelengths of the light rays.

Different surfaces absorb, transmit or reflect the different wavelengths of visible light in different ways.

Advanced non-gcse note: Many of the differences in colour are due electronic changes caused by the photons hitting the surface, or being transmitted through the material e.g. the colours of transition metal compounds (GCSE chemistry notes).

Even the size of solid particles can affect the 'shade' of a colour and sometimes a material in a very finely divided form can have a completely colour than the bulk material.

If you want to forge a Van Gogh you will have trouble getting the correct shade for his famous yellow coloured sunflowers! You need the right particle size of the chrome yellow pigment.

Selected technical data on the colours of the visible spectrum

The figures quoted for wavelength and frequency are 'typical mid-range' for that colour.

Narrow bands of wavelengths/frequencies would look the same colour to us.

Visible colour ir and uv for comparison	wavelength (nm)	frequency in 10¹⁴ Hz	What you see via your eye!	Photon energy in kJ/mol	wavenumber in 10⁴ cm^-1
infrared (invisible to us)	1000	3.0	invisible to us	120	1.00
RED	700	4.3		171	1.43
ORANGE	620	4.8		193	1.61
YELLOW	580	5.2		206	1.72
GREEN	530	5.7		226	1.89
BLUE	470	6.4		254	2.13
INDIGO	445	6.8		285	2.26
VIOLET	420	7.1		343	2.38
near ultraviolet (invisible)	300	10	invisible to us	400	3.33
far ultraviolet	200	15	invisible to us	600	5.00
				for doc b's reference only - ignore!	for doc b's reference only - ignore!

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

Key points for COLOUR - colours - wavelengths and frequencies

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-friendly summary of the key concepts around colour and visible light tailored for students preparing for GCSE/IGCSE Physics across WJEC, CCEA, CIE, AQA, Edexcel, and OCR:

What Is Colour?

Colour is how we perceive different wavelengths of visible light.
Each colour corresponds to a specific range of wavelengths and frequencies.
Opaque objects appear coloured because they reflect certain wavelengths and absorb others.
White objects reflect all visible wavelengths equally.
Black objects absorb all visible wavelengths.
See other sections on the visible spectrum and colour of objects

What Is Visible Light?

Visible light is the part of the electromagnetic spectrum that can be detected by the human eye.
It lies between infrared and ultraviolet radiation.
It consists of seven colours: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV).
These colours form a continuous spectrum.

Frequencies and Wavelengths of Visible Light

Colour	Wavelength (nm)	Frequency (THz) (1 THz is 10¹² Hz)
Red	~620-750	~400-484
Orange	~590-620	~484-508
Yellow	~570-590	~508-526
Green	~495-570	~526-606
Blue	~450-495	~606-668
Indigo	~425-450	~668-706
Violet	~380-425	~706-789

Tip: Wavelength and frequency are inversely proportional — as one increases, the other decreases.

Colour Filters and Appearance

Filters absorb some wavelengths and transmit others.
A red filter transmits red light and absorbs all others.
An object appears black under a filter if it reflects a colour that the filter blocks.
See other sections on the visible spectrum and colour of objects

Required Practical Knowledge

Investigate reflection and refraction using ray boxes and transparent blocks.
Use colour filters to observe how objects appear under different lighting.
Understand specular vs. diffuse reflection.
See reflection, visible light, ray box experiments, ray diagrams, mirror uses
See refraction and diffraction, prism investigations, ray diagrams explained

Exam Tips for Students

Use the correct terminology: e.g., “transmit,” “absorb,” “reflect.”
Draw ray diagrams to show how light behaves with mirrors, prisms and filters (links above).
Revise the EM spectrum and know where visible light fits.
Practice past paper questions from your specific exam board.
Remember units: wavelength in nanometres (nm), frequency in terahertz (THz).

Keywords, phrases and learning objectives for data on visible light and colour - order of colours and trend in wavelengths and frequency

Know what we mean by colour i.e. the colours we observe of the visible region of the electromagnet spectrum.

Know the order of the colours of the visible spectrum in terms of wavelength and frequency.

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