Question

An object is placed at a distance of $10cm$ from a convex lens of power $5D$. Find the position of the image :

• A. - 20 cm
• B. 30 cm
• C. 20 cm
• D. - 30 cm

Answer 1

Answer: (C)

The focal length of the convex lens
$f=\frac{1}{P}m$
or $f=\frac{1}{5}\times 100cm$
or $f=20cm$
From the relation, we get
$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$
Here, $f=20cm,u=-10cm$
Therefore, $\frac{1}{v}=\frac{1}{u}+\frac{1}{f}$
$=\frac{1}{-10}+\frac{1}{20}$
$=\frac{-2+1}{20}=-\frac{1}{20}$
Hence, $v=-20cm$
Therefore, the image will be formed at a distance of $20cm$ on the same side of the object.