Name the part of the human eye that helps in changing the focal length of the eye lens.

Which of the following is true for the eye defect known as hypermetropia (farsightedness)?

$A$ student cannot read properly from the blackboard while sitting on the front desk in a large classroom. However,he can read clearly while sitting on the last desk of the classroom.
$(a)$ Draw ray diagrams to illustrate the formation of the image of the blackboard writing by his eye lens when he is seated at the $(i)$ front desk,$(ii)$ last desk.
$(b)$ Name the defect of the eye from which the student is suffering.
$(c)$ Name the type of lens that would enable him to see the blackboard writing clearly when seated at the front desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.

$A$ bifocal lens consists of both concave and convex lenses. Bifocal lenses are required by a person suffering from $.............$.
$P$ - Myopia (nearsightedness)
$Q$ - Hypermetropia (farsightedness)
$R$ - Presbyopia

$A$ student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?

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.