Question

(a) A student suffering from myopia is not able to see distinctly the objects placed beyond `5 m`. Two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain :
(i) Why the student is unable to see distinctly the objects placed beyond `5 m` from his eyes.
(ii) The type of corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If in this case, numerical value of focal length of corrective lens is `5 m`, find the power of the lens as per the new cartesion sign convention.

Answer 1

(a) Two possible reasons:
- The eye ball size might have got elongated.
- The eye lens is more thick than its normal thickness during its power of accomodation.

`f= -5 m" (since lens is concave), "P=? `
`P=(1)/(f)=(1)/(-5)=0.2` Diopter
Power of correcting lens is -0.2 D and this correcting lens is concave lens.