$A$ 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

Which liquid fills the space behind the cornea?

$A$ 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?

$A$ $14$ year old student is not able to see clearly the questions written on the blackboard placed at a distance of $5\, m$ from him.
$(a)$ Name the defect of vision he is suffering from.
$(b)$ With the help of labelled ray diagrams show how this defect can be corrected.
$(c)$ Name the type of lens used to correct this defect.

$A$ student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw a ray diagram for the correction of this defect.

$A$ person suffering from an eye defect uses lenses of power $-1 \,D$. Identify the eye defect. Draw a suitable diagram to illustrate how this type of lens corrects the defect. Give the nature of the corrective lens to be used. Also,calculate the focal length of the corrective lens.