# Homework Help: Two Lenses Problem

1. Sep 23, 2012

### HarryHo90sHK

1. The problem statement, all variables and given/known data

Extracted from NSS Physics at Work Book 3A, a textbook published by Oxford University Press.
An object O is placed at distance u from the optical centre of convex lens A. The focal length of the lens is f1, where f1 > u. An image I' is formed.
(b) Another convex lens B is added in contact with lens A. The focal length of lens B is f2. The lenses are thin, such that the distance between the two optical centres is small compared to the object distance and the image distance. The image I' is acting as the object for lens B.
(i) What is the relation between the object distance u' for lens B and the image distance v' for lens A?
(ii) Hence write the equation which relates the image distance v with v' and f1.

2. Relevant equations

Lens Formula: 1/f = 1/u + 1/v

3. The attempt at a solution

Unable to find the solution.

(b) (i) u' = -v'
(b) (ii) 1/f2 = 1/-v' + 1/v

5. My question is...

What is the ray diagram with lenses A and B exactly like?

Last edited: Sep 23, 2012