$A$ 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.

(N/A) $(i)$ When the student sits at the front desk,the object is too close. The light rays from the blackboard focus behind the retina,resulting in a blurred image on the retina.
$(ii)$ When the student sits at the last desk,the object is at a sufficient distance. The light rays from the blackboard focus exactly on the retina,resulting in a clear image.
$(b)$ The student is suffering from hypermetropia,also known as long-sightedness.
$(c)$ This defect can be corrected by using a convex lens of suitable focal length. The convex lens converges the light rays before they enter the eye,allowing the image to be formed on the retina.