Question

An object (O) is placed in a medium M of refractive index 5/3. A convex lens of focal length 15 cm is placed in front of the object as shown in the figure. Determine the position of the image formed by the lens.

• A. 15 cm
• B. 20 cm
• C. 30 cm
• D. 60 cm

Answer 1

The correct option is D 60 cm


we will observe object at apparent position and we know that $\nu =\frac{realdepth}{apparentdepth}$
Hence $apparentdepth=\frac{10}{5}/3=6cm$
So total $u=-20cm$
and focal length of lens $=15cm$(given)
By Lens formula
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}+\frac{1}{20}=\frac{1}{15}$
$\frac{1}{v}=\frac{1}{15}-\frac{1}{20}=\frac{5}{15/20}$
$v=60cm$