Question # 16 from chapter 3 in "Introduction to Optics" by Pedrotti,
second edition.

A plano-convex lens having a focal length of 25.0 cm is to be made
with glass of refractive index 1.520. Calculate the radius of
curvature of the convex side of this lens

Hello again al3in, I decided to learn a little more about optics.

http://cvu.strath.ac.uk/courseware/msc/jbaggot/lenses/lenses.html

This is a basic equation used to calculate the focal length of a lens
given the radius of curvature of the lens and the refractive index of
the lens relative to the medium. It is only an approximation and works
best for thin lenses.


1/f = (n-1)(1/R1 - 1/R2)    where n is the refractive index of the lens 

For a plano-convex lens R2 is flat. Therefore, 1/R2 is 1/infinity or zero.

The formula then becomes:

1/f = (n-1)(1/R1)

Plugging in your values:

1/25cm = (1.520 - 1)(1/R1)

1/25cm = 0.52 / R1

R1 = 25cm x 0.52 = 13cm

Hope this makes sense to you, Redhoss

Perfect answer. Thanks alot.