Q1. Two identical prisms P1 and P2 are placed as shown in the figure. A narrow beam of white light is incident on glass prism P1, as shown in the figure. The emergent beam from prism P1 falls on the second prism P2. The resulting emergent beam from prism P2 on the screen contains:
Explanation
A glass prism disperses white light into its constituent colours because different colours deviate by different amounts. When a second identical prism is placed in the reverse arrangement, it produces the opposite deviation and recombines the separated colours. Therefore the beam reaching the screen is white light again. A VIBGYOR spectrum from top to bottom or bottom to top would be seen if the colours remained separated after the second prism, which is not the case here. No light is also incorrect because the prisms refract and recombine the beam; they do not block it.