A child is able to read his book comfortably but is unable to read the matter written on the blackboard at a certain distance.

(i) Name the defect of vision he's suffering from.

(ii) With the help of labeled ray diagrams show :

    $\left(a\right)$ the above-mentioned defect of vision.

    $\left(b\right)$ correction of the above-mentioned defect using a suitable lens.

Study the diagram below and answer the following question :

(i) Name the defect of vision depicted in the diagram.

(ii) List two causes of the said defect.

(iii) Draw a ray diagram for the correction of the above defect using an appropriate lens.

$\left(a\right)$ Ravi kept a book at a distance of $10 \mathrm{cm}$ from the eye of his friend Hari. Hari is not able to read anything written in the book. Explain why? 

$\left(b\right)$ A lens of focal length $5 \mathrm{cm}$ is being used by a student in the laboratory as a magnifying lens. His least distance of distinct vision is $25 \mathrm{cm}$. What magnification is the student getting? 

$\left(a\right)$ A student is suffering from myopia is not able to see distinctly the objects placed beyond $5 \mathrm{m}$. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain :

$\left(i\right)$ why the student is unable to see distinctly the objects placed beyond $5 \mathrm{m}$ from his eyes?

$\left(ii\right)$ the type of corrective lens used to restore proper vision and how this defect is corrected by the use of this lens

$\left(b\right)$ If, in this case, the numerical value of the focal length of the corrective lens is $5 \mathrm{m}$, find the power of the lens as per the new cartesian sign convention.