# Optics Problem

dlaszlo88
I have this Physics Problem which I am not to sure where to start it from. The problem is:

A real inverted image I of an object O is formed by a certain lens. The object-image speration is d = 0.40m, measured along the central axis of the lens. The image is just half the size of the object. There is a figure to this problem and its an object O larger than image I. I is a smaller and inverted, the lens has to go in between the object and image.

They ask you what kind of lens must be used to produce this image? I know that it should be a converging lens.
Then they ask How far from the object must the lens be placed and what is the focal length of the lens.

I think that the intial step is to look at the lateral magnification which is 1/2 But from there I am stuck. In order to find part C I know it will be easy just the second part is giving me a hard time. Any help will be greatly appreciated.

amcavoy
Is this problem from the Halliday / Resnick / Walker book?

dlaszlo88
Yes that is my textbook

well, the problem gives you the distance from image to object.

the problem also gives you the magnification (sign and all!).

use the appropriate equation for magnification...

and now you can reduce the problem to a simple algebraic equation to find the distances from the object to the lens and the image to the lens.

(remember that "p" is the distance from the object to the lens and "q" is the distance from the image to the lens.)

and once you have those two distances, you can find the focal length, no problem, using the correct equation. ...you should be able to do this! 