Question

Suppose white light going through a prism is split into its constituent colours and half of them are blocked by a piece of paper. Now, the remaining colours are kept in front of an identical inverted prism. What will happen?

• A. The remaining colours combine to give white light.
• B. The remaining colours combine to give a different coloured light.
• C. The colours get further dispersed.
• D. The light goes through unchanged and unhindered.

Answer 1

The correct option is B The remaining colours combine to give a different coloured light.

White light is a spectrum of colours. So, combining the same spectrum of colours will give back white light. This can be done with an inverted prism.
The prism can be used to split any light into its contituent spectrum, not only white light. The prism can also be used to combine a spectrum of colours to give a different coloured light.

So, blocking half the colours coming out of the first prism leaves a smaller portion of the spectrum which will give a different coloured light on recombining going through the second or inverted prism.