Question

a convex lens dipped in a liquid, whose refractive index is equal to refractive indexof material of lens. then its focal length will-

Answer 1

Focal length Become infinite

Answer 2

Focal length of liquid dipped convex lens will be infinite.

Explanation:

The reason behind is that the convex lens must be having refractive index according to the material made up of, and when it is placed in the liquid of the same refractive index.  

Lens Maker’s formula, $\bold{\begin{array}{l}{\frac{1}{f}=\left(^{\prime} \mu_{2}-1\right)\left(\frac{1}{R_{1}}-\frac{1}{R_{2}}\right)} \\ {\frac{1}{f}=0, f=\infty}\end{array}}$

The focal length of combination becomes infinite, due to the reason that refractive index of combination is the ratio of the refraction caused in the two media whose ratio becomes infinite.