If the eye is kept very close to a coverging lens (focal length `= 10 cm`) and at the optical centre of the lens and an object is kept at distance 'd' of the object from the lebs so that its image can be seen clearly by the defect free eye is :
.

Options

A. 10 cm
B. 25 cm
C. `(50)/(3) cm`
D. `(50)/(7) cm`

Answer

D

Explanation

Using, `(1)/(v)-(1)/(u)=(1)/(F) rArr (1)/(d) +(1)/((-d'))=(1)/(F)`
(where d' is the image of the object from the lens, which behaves as the object for the eye)
`rArr (1)/(d) =(1)/(F) +(1)/(d')`
For minimum d,d' should be minimum which is equal to 25 cm for eye.
Substituting ,
`rArr (1)/(d)=(1)/(25)+(1)/(10)=(10+25)/(250) =(7)/(50)`
`rArr d =(50)/(7)`