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Colours come from light interacting with eye light receptors. Colour is the visual attribute of objectsThe study of colour is referred to as chromatics. This study includes the humans ability to see colour, the origin of colour in materials, colour theory and the physics of radiation in the human visible range. 

Most light sources are mixtures of various wavelengths of light. Many sources can produce a spectral of colours as the eye cannot distinguish them from single wavelength sources. Most human colour perception can be created by mixing a combination of three colours called primaries. These colours are red, yellow, and blue.

Colour Wavelength interval Frequency Interval
red ~ 700-635 nm ~ 430-480 THz
orange ~ 635-590 nm ~ 480-510 THz
yellow ~ 590-560 nm ~ 541-540 THz
green ~ 560-490nm ~ 540-610 THz
blue ~ 490-450 nm ~ 610-670 THz
purple ~ 450-400 nm ~ 670-750 THz


A rose coloured mineral specimen is given to you for identification. It has a conchoidal fracture, no streak, and a non-metallic lustre. It can be scratched with a steel file, but not with glass or a pocket knife blade. It has no streak. Its mass is 53 grams. You place it in water and it displaces a volume of 20 cubic centimetre

Convex Lens Colour

A convex lens is placed on a flat glass plate and illuminated from above with monochromatic red light. When viewed from above, concentric bands of red and dark are observed. What does one observe at the exact center of the lens where the lens and the glass plate are in direct contact? a. a bright spot that is some color other