Question

If white ray falls on the system as shown in the given diagram, then how many colours will we see after all dispersions have happened?

• A. Only 1 white ray
• B. 7 different colours
• C. Only red colour
• D. Only violet colour

Answer 1

The correct option is B

7 different colours

After passing through the first prism, white light will split into its constituent 7 colours.
Since the base of the next prism is in opposite direction, it will recombine all the seven colors and form the single white light again. This emergent ray is parallel to the incident ray.
When this white light ray is incident on the third prism, it will again disperse into 7 different colours from the 3rd prism. Finally, we will have all the 7 colours.