Is the position of a star as seen by us its true position? Justify your answer.

In the figure,a ray of light $PQ$ is incident normally on one face $AB$ of an equilateral glass prism. What are the angles of incidence at faces $AB$ and $AC$?

What is meant by the least distance of distinct vision? How does this vary between the very young and old people?

$A$ prism causes dispersion of white light while a rectangular glass block does not. Explain.

$A$ person cannot read a book at distances less than $50\, cm$. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams to show the image formation
$(i)$ by defective eye and
$(ii)$ after using corrective lens.

$A$ person needs a lens of power $-2.5 \ D$ for correcting his vision. Name the defect of vision he is suffering from. Which lens will he be using for the correction? Also,find the focal length of the lens.