Question

The focal length of an equiconvex lens is greater than the radius of curvature of any of the surfaces.Then the refractive index of the material of the lens is

• A. greater than 0 but less than 1.5
• B. greater than 1.5 but less than 2.0
• C. greater than 2.0 but less than 2.5
• D. greater than 2.5 but less than 3.0

Answer 1

The correct option is A greater than 0 but less than 1.5

$\frac{1}{f}=(\mu -1)\left(\frac{2}{R}\right)$

$f>R$

$\frac{f}{R}>1$

$\frac{R}{F}=(\mu -1)2$

$\frac{R}{F}<1\Rightarrow (\mu -1)2<1$

$\mu -1<1/2$

$\mu <3/2$