Question

A convex lens is made of a material having refractive index 1.2. Both the surfaces of the lens are convex. If it is dipped into water $(\mu =1.33).$ It will behave like

• A. a convergent lens
• B. a divergent lens
• C. a rectangular slab
• D. a prism.

Answer 1

The correct option is B a divergent lens

Applying Lens' maker formula;
$\frac{1}{f}=(\frac{{\mu }_2}{{\mu }_1}-1)(\frac{1}{R_I.}-\frac{1}{R_2})$
${\mu }_1$ is the R.I of water here;
We get;
$\frac{1}{f}=(\frac{1.2}{1.3}-1)(\frac{1}{R}-\frac{1}{R})$
We see f is -ve.
Hence, it will behave as a divergent lens.