Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Two Radii Lens

  1. Mar 30, 2005 #1
    A piece of glass has two radii. The left side has a radius of 2 cm and the right has a radii of 4 cm. The two are seperated by 8 cm. There is a point object 1 cm left of the glass, find the position of the image.

    I need to use the equation

    n2-n1/R = n1/do + n2/di, i need to use it twice, once for each radius, and one time it would be negative (the radius).

    1.5-1 / .02 = 1/.01 + 1.5/di

    Solved it and got di=2 cm

    1.5-1/-.04 = 1/.09 + 1.5/di

    Solved it got di to be -12 cm.

    Combined the two to get -12 + 2 = -10 cm..10 cm behind the piece of glass...does this seem right?
  2. jcsd
  3. Mar 30, 2005 #2


    User Avatar

    Staff: Mentor

    For the second surface, the "object" is not the original object, but instead, the image formed by the first surface. So the object distance in the second step is the distance from the second surface to the image that you calculated in the first step. The second image distance is the final image distance (from the second surface).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook