Question

A small fish, 4 cm below the surface of a lake, is viewed through a thin converging lens of focal length 30 cm held 2 cm above the water surface. Refractive index of water is 1.33. The image of the fish from the lens is at a distance of :

• A. 10 cm
• B. 8 cm
• C. 6 cm
• D. 4 cm

Answer 1

The correct option is C 6 cm

We have the equation,

$\frac{1}{v}-\frac{1}{u}=\frac{1}{30}$

$⟹\frac{1}{v}-\frac{1}{-5}=\frac{1}{30}$

$⟹\frac{1}{v}=\frac{1}{30}-\frac{6}{30}$

$⟹\frac{1}{v}=-\frac{5}{30}$

$v=-6cm$

So, the image is formed at a distance of $6cm$ from the lens.