Question

Point object O is placed on the principal axis of a convex lens of focal length $20cm$ at a distance of $40cm$ to the left of it. The diameter of the lens is $10cm$. If the eye is placed $60cm$ to the right of the lens at a distance $h$ below the principal axis, then the maximum value of $h$ to see the image is :

• A. $0$
• B. $5cm$
• C. $2.5cm$
• D. $10cm$

Answer 1

The correct option is C $2.5cm$

For the refraction of the point object from the lens,

$\frac{1}{v}-\frac{1}{-40}=\frac{1}{20}$

Hence , $v=40cm$

Figure clearly suggests that for the eye to be able to see the image,

$\frac{40cm}{5cm}=\frac{20cm}{h}$

Hence, $h=2.5cm$