Question

by using two prism how do we get white light?

Answer 1

By using one prism, you will get a spectrum. Now take another prism and place inverted to first prism so again you will get white light.

Discovery by Issac Newton...

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Answer 2

Place the glass prism in such manner that the sunlight through the window falls on one side of the prism and then on the white wall. You can see that thelight reflected on the wall has several colors. The prism splits the white lightinto seven different colors.

Now place an other prism as shown in the image and we will have the combination of all the colours and giving us white back again.