$A$ person has to use a concave lens in his spectacles. Which defect of vision is he suffering from?

What is the method of obtaining various colors by mixing primary colors in appropriate proportions called?

$A$ glass slab is placed over a page on which the word $VIBGYOR$ is printed with each letter in its corresponding colour. $(i)$ Will the image of all the letters be in the same place? $(ii)$ If not, state which letter will be raised to the maximum. Give a reason for your answer.

Why can you not see an object clearly if it is placed very close to your eye?

Which part of the eye controls the amount of light entering the eye?

The twinkling of stars is due to atmospheric: