$A$ person is advised to wear spectacles with concave lenses. What type of defect of vision is he suffering from?

$A$ 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.

What is meant by the near point of the eye?

What is the eye lens made of?

What is the far point of a person with normal vision?

$(a)$ How does the sky appear from the surface of the moon?
$(b)$ What is the cause of the blue colour of the ocean?