PUC Karnataka Science Class 12Department of Pre-University Education, Karnataka
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# 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. - PUC Karnataka Science Class 12 - Physics

#### 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 =R1

Radius of curvature of the other face of the lens =R2

Radius of curvature of the double-convex lens = R

∴ R1=R and R2=-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

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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.
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