06.
Double convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces having the same radius of curvature. What is the radius of curvature required if the focal length of the lens is to be 20 cm?
Suggested solution:
m = 1.55, R1 = R and R2 = -R, f = 20 cm
or
\ R = 40 x 0.55 cm = 22 cm 