How is astigmatism corrected?

The far point of a myopic person is $40 \, cm$. What type of lens should they wear to see distant objects clearly? Calculate the focal length and the power of the lens they should use.

What kind of lens is used in the spectacles of a person suffering from myopia (near-sightedness)?

$(a)$ 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 is meant by the near point of the eye?

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 $AC$?