Prism is a block of glass with triangular cross section.when a white light is pass through the prism it splits into 7 colours b/c white light is consist of & colours. The light waves are refracted as they enter the prism and leave the prism.The shorter the wavelegnth of light the ore it is refracted.
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actually the white light we is composed of seven colors and when light passes through a prism it got spits into seven colors.