Question

A convergent (biconvex) lens is placed inside a jar filled with a liquid. The lens has focal length $20cm$, when in air and its material has a refractive index of $1.5$. If the liquid has a refractive index of $1.6$, the focal length of the lens while in the jar is

• A. $-110cm$
• B. $-130cm$
• C. $-160cm$
• D. $-180cm$

Answer 1

The correct option is C $-160cm$

focal length in liquid $\frac{(1.5-1)f_{air}}{\left(\right(1.5/1.6)-1)}=-160cm$

Option C is correct.