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 School-college Physics Notes: Visible spectrum-colour 2. What is colour?

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

Doc Brown's Physics exam study revision notes

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.

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


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

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