The radius of curvature of each surface of a double convex lens is 15 cm and the refractive index of the medium of the lens is 1.5. What is the focal length of the lens ?

15 cm

The correct answer is Option (4) → 15 cm

$\frac{1}{f}=(n-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$ [Len's maker formula]

Given,

$R_1=15cm$

$R_2=-15cm$

$n=1.5$

$∴\frac{1}{f}=(1.5-1)\left(\frac{1}{15}-\frac{1}{-15}\right)$

$\frac{1}{f}=\frac{1}{15}$

$f=15cm$