Question

how can we see band of different colours on white paper

Answer 1

Answer:

Put a thin strip of white paper on a dark surface and look at it through a prism. You have to look in a different direction, and due to the differences in the refractive index for the different wavelengths of light, the strip now looks coloured.

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Answer 2

first we ll give out a white light and then put a glass prism in between and put the white paper backside prism.