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Note On Primary and Secondary Colours

Primary and Secondary Colours: Red, green and blue colours are primary colours. When they are mixed equally, white light is produced. Others such as yellow, magenta, and cyan are called secondary colours.

The adding of primary colours to produce other colours is known as additive colour mixing.

Red and blue produce magenta

Red and green produce yellow

Blue and green produce cyan

Secondary colours are magenta, yellow and cyan while complimentary colours are colours which can be added to get white.

Red and cyan produce white

Blue and yellow produce white

Green and magenta produce white

Colour triangle

primary and secondary colours

Colours of objects

Colour of an opaque object is due to selective reflection, when white light falls on an object, it absorbs all colours except its characteristics colour which it reflects. A red object appears red because it absorbs all other colours except red which it reflects. If a red object is viewed in green or blue light it will appear dark because this light do not contain red. But in yellow light it will look red.

Questions on primary and secondary colours

(1) The angle of deviation of light of various colours passing through a triangular prism increases in the order

A. blue → green → red

B. red → green → blue

C. green → violet → blue

D. blue → red → green

Red is the least deviated while violet is the most deviated. From ROYGBIV, Red – Orange -Yellow – Green- Blue – Indigo – Violet. B is the correct answer

(2) Disperson of white light is the ability of white light to

A. Penetrate air, water and glass

B. Move in a straight line

C. Move around corners

D. Separate to its component Colours

The separation of colours by prism is referred to as dispersion. D is the right answer

(3) When a red rose flower is observed in blue light, what colour does the observer see?

A. Yellow   B. Red   C. Blue     D. Magenta.

Red and blue produce magenta. D is the right answer

(4) Which of the following is a secondary colour?

A.Blue       B. Orange     C. Red         D. Green.

Blue, red, and green are primary color except orange. B is the right answer

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