A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double of the other. Find the radii, if the refractive index of the material of the lens is 1.5.
Focal length of double convex lens= f=25 cm
Refractive index of the lens = 
= 1.5
According to the question, radius of curvature of one surface is twice the other surface.
i.e. 
(According to sign convention)
By using the lens makers’ formula;
We get;
Radius = 
& Radius 
1