Question

how does a prism separates the seven constituents colours of a white light

Answer 1

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in a material medium light rays of different colours propagate with different speed.
in glass, the speed of violet colour is minimum while that of red colour is maximum.
Hence a ray of red colour bends minimum towards the base of the prism while a ray of violet colour bands the maximum.
thus, white light splits into its constituent colours - from red to violet. this makes prism separate the seven constituent colour.

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hope it will help you :^)

Answer 2

These colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersion.