A convex lens made of glass (µ = 1.5) has both radii of curvature 20 cm each. A point object is placed on the principal axis at a distance of 40 cm from the lens. The distance of the image from the lens is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 40 cm
According to len's Maker formula -
$\frac{1}{f}=(μ-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$
$⇒\frac{1}{f}=(1.5-1)\left(\frac{1}{20}-\frac{1}{20}\right)=\frac{1}{20}$
$⇒f=20cm$
On using the lens formula
$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$
$⇒\frac{1}{20}=\frac{1}{v}-\frac{1}{-40}⇒v=40cm$