Rainbow:

Rainbow: rainbow is the coloured display in the form of an arc of a circle hanging in the sky observed during or after a little drizzle appearing on the opposite side of sun. Rainbow is formed due to dispersion of sun light by the suspended water droplets.

Rain bow is of two types: (i) primary rainbow (ii) Secondary rainbow

Primary rainbow is formed due to two refractions and one total internal reflection of light falling on the raindrops. In the primary rainbow, the red clour is on the convex side and violet on the concave side, primary rainbow has an angular width of 2˚ at an average angle of elevation of 41˚.

Secondary rainbow is formed due to two refractions and two internal reflections of light falling on rain drops. The order of colour on the secondary rainbow is in the reverse order and has an angular width of 3.5˚ at an average elevation of 52.75˚. Secondary rainbow is less intense than primary rainbow.

Theory of Colours: Colour is the sensation perceived by the rods in the eye due to light.

Primary Colours: The spectral colours blue, green and red are called primary colours because all the colours can be produced by mixing these in proper proportion.

Blue + Red + Green = white

Secondary Colours: the colour produced by mixing any two primary colours is called a secondary colour. There are three secondary colours yellow, magenta and cyan as

Green + Red = Yellow     Red + Blue = Magenta     Blue + Green = Cyan

When the three secondary colours are mixed, white colour is produced

Yellow + magenta + Cyan = White