The visible range of the spectrum is seen as various colours, with the colour depending on the wavelength.The longest waves are red, moving through every colour, with violet being the shortest wavelength (Fig 14.15). Although it is obvious all colours are present in the rainbow, only seven are referred to and need to be learnt off.
The mnemonic Richard Of York Gave Battle In Vain may help you to memorise the colours ‘Red Orange Yellow Green Blue Indio Violet’ (Fig 14.14).
Red Richard
Orange of
Yellow York
Fig 14.14: Colours of the rainbow (spectrum)
Primary, Secondary and Complementary Colours
White light can be produced by combining just three colours (of equal intensity).These three colours are the primary colours: red, green and blue. All other colours can also be produced by combining the three in varying ratios.
When two primary colours (of equal intensity) are mixed you get a secondary colour. These are shown in Fig 14.16. blue red magenta; green blue cyan; red green yellow
You get white light by mixing a primary colour and the opposite secondary colour. These colours are called complementary colours.
The mnemonic Before You Get Married Ring Cindy White may help you to memorise the complementary pairings ‘Blue – Yellow; Green – Magenta; Red – Cyan’ and the colour you get by mixing them, namely white.
DEMONSTRATION 14.3
Demonstration of Addition of Colours Apparatus Blue, green and red light sources, white screen
Procedure
Shine equal intensities of each colour onto the screen and overlap the colours. Observation
The colours mix as illustrated in Fig 14.16.
Conclusion blue red magenta; green blue cyan; red green yellow; blue green red white
Red Magenta
Yellow White
Fig 14.16 Cyan Blue
Fig 14.15: The different colours are merely different wavelengths of light
