JEE Main & Advanced Physics Ray Optics Colours of Objects

Colours of Objects

Category : JEE Main & Advanced

Colour is defined as the sensation received by the eye (rod cells of the eye) due to light coming from an object.

(1) Colours of opaque object : The colours of opaque bodies are due to selective reflection. e.g.

(i) A rose appears red in white light because it reflects red colour and absorbs all remaining colours.

(ii) When yellow light falls on a bunch of flowers, then yellow and white flowers looks yellow. Other flowers looks black.

(2) Colours of transparent object : The colours of transperent bodies are due to selective transmission..

(i) A red glass appears red because it absorbs all colours, except red which it transmits.

(ii) When we look on objects through a green glass or green filter then green and white objects will appear green while other black.

(3) Colour of the sky : Light of shorter wavelength is scattered much more than the light of longer wavelength. Since blue colour has relatively shorter wavelength, it predominates the sky and hence sky appears bluish.

(4) Colour of clouds : Large particles like water droplets and dust do not have this selective scattering power. They scatter all wavelengths alomost equally. Hence clouds appear to the white.

(5) Colour triangle for spectral colours : Red, Green and blue are primary colours.

(i) Complementary colours : Green and Magenta, Blue and Yellow, Red and Cyan.

(ii) Combination : Green + Red + Blue = White, Blue + Yellow = White, Red + Cyan = White, Green + Magenta = White

(6) Colour triangle for pigment and dyes : Red, Yellow and Blue are the primary colours.

(i) Complementary colours : Yellow and Mauve, Red and Green, Blue and Orange.

(ii) Combination : Yellow + Red + Blue = Black, Blue + Orange = Black, Red + Green = Black, Yellow + Mauve = Black

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