Posted by Anonymous on Monday, March 23, 2009 at 11:39am.
1) A convex lens with a focal lenght of 4.0cm is placed 20.0cm from a concave lens with a focal lenght of 5.0cm. Find the position of the image when the object is placed 12.0c, in front of the convex lens.
2) A double concave lens has a refractive index of 1.5 radii of curvature of 10.0cm and 15cm. Determine its focal length.
Thank you for helping in advance!

Physics: Lenses  drwls, Monday, March 23, 2009 at 2:49pm
1) Use the position of the image formed by the first lens as the location of the object for the second lens.
For the distance of the image from the first lens, di, use
1/12 + 1/di = 1/4
1/di = 2/12
di = 6
That means the first image is 20  6 = 14 cm in front of the concave lens, which has a negative focal length. For the location of the final image, di', use
1/14 + 1/di' = 1/5
2) For this problem, use the "lens maker's formula". If it is not in your textbook, you can find it at
http://scienceworld.wolfram.com/physics/LensMakersFormula.html
Both of the "1/R" terms will be negative. The focal length will be negative.

Physics: Lenses  Anonymous, Monday, March 23, 2009 at 3:20pm
Thank you drwls for your help!
Answer This Question
Related Questions
 physics  A 15.0cm object is placed 60.0cm from a convex lens which has a focal ...
 PHYSICS PLEASE HELP ASAP  When an object is placed 55.0cm from a certain ...
 physics  Because a concave lens cannot form a real image of a real object, it ...
 Physics  An object is placed 30mm in front of a lens. An image of the object is...
 physics (mirror)  a diverging mirror of 52.0 focal lenght produces a virtual ...
 Physics  A 5.0cm tall object is placed 16cm from a convex lens with a focal ...
 Physics  A simple camera telephoto lens consists of two lenses. The objective ...
 Physics ( optics)  A simple camera telephoto lens consists of two lenses. The ...
 physics  a convex mirror has a focal length of 10.0cm. what is the image ...
 Physics  A simple camera telephoto lens consists of two lenses. The objective ...
More Related Questions