Question

Double convex lenses are to be manufactured from a glass of refractive index 1.5 v with both faces of the same radius of curvature what is the radius of curvature required if the focal length is to be 20 cm

Answer 1

given : Rμ=1.55R1=RandR2=−Rf=20cmμ=1.55R1=RandR2=−Rf=20cm

1f=(μ−1)[1R1−1R2]1f=(μ−1)[1R1−1R2]

=> 120120=(1.55−1)(1R+1R)=(1.55−1)(1R+1R)

=1.10R=1.10R

R=20×1.1=22cmR=20×1.1=22cm

Answer : 22cm