Question

The near point and far point of a person are 40 cm and 250 cm respectively. Determine the power of the lens he/she should use while reading a book kept at distance 25 cm from the eye.

• A. 2.5 D
• B. 5.0 D
• C. 1.5 D
• D. 3.5 D

Answer 1

The correct option is C 1.5 D

The lens should be such that it shifts the image of object at 25cm from eye to the near point of the defected person.

Hence the lens would follow the following lens equation,

$\frac{1}{f}=P=\frac{1}{v}-\frac{1}{u}$

$=\frac{1}{-0.4}-\frac{1}{-0.25}$

$=1.5D$