What is long-sightedness (hypermetropia)?

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

The eye defect known as $Presbyopia$ is corrected by using a $........$ lens.

Write the value of the near point of distinct vision for a normal eye.

$A$ person cannot see objects farther than $12\, m$ from the eye clearly. Name the defect of vision he is suffering from and the lens that should be used for correction of this defect. Illustrate with the help of a diagram,how this lens will correct the defective vision?

Why does the clear sky appear blue? How would the sky appear in the absence of Earth's atmosphere?