#### Question

A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.

#### Solution

Refractive index of glass, μ=1.55

Focal length of the double-convex lens, f=20 cm

Radius of curvature of one face of the lens =R_{1}

Radius of curvature of the other face of the lens =R_{2}

Radius of curvature of the double-convex lens = R

∴ R_{1}=R and R_{2}=-R

The value of *R* can be calculated as:

`1/f=(mu-1)[1/R_1-1/R_2]`

`1/20=(1.55-1)[1/R+1/R]`

`1/20=(0.55)[2/R]`

`therefore R=22 cm`

Hence , the radius of curvature of the double-convex lens is 22 cm

Is there an error in this question or solution?

Solution A Double Convex Lens is Made of a Glass of Refractive Index 1.55, with Both Faces of the Same Radius of Curvature. Find the Radius of Curvature Required, If the Focal Length is 20 Cm. Concept: Reflection of Light by Spherical Mirrors.