When a beam of white light is passed through a prism,violet colour bends the most and red colour the least.

Which of the following colors are primary colors?

$(a)$ Explain with the help of a labelled diagram how a combination of two prisms can be used so that incident white light emerges out of the second prism as white light.
$(b)$ Name the scientist who first performed this activity.
$(c)$ Explain the term spectrum in brief.

What are the colors obtained by mixing primary colors called?

$A$ person is unable to read a book clearly when kept at a distance of $25 \,cm$ from his eye. Name the defect. How can it be corrected? Draw ray diagrams for $(i)$ defective eye $(ii)$ corrected eye and explain them.

When red and green light overlap,what color does that region appear?