Question

The size of the image of an object, which is at infinity, as formed by a convex lens of focal length
30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convex lens and the
image at a distance of 26 cm from the convex lens, calculate the new size of the image

• A. 1.25 cm
• B. 2.5 cm
• C. 1.05 cm
• D. 2 cm

Answer 1

Answer: (B)

$u=+4$

$f=-20$
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{v}-\frac{1}{4}=\frac{-1}{20}$

$v=+5$

size of image is $\frac{5}{4}\times 2=2.5$

option $B$ is correct