Solving a Focal Length Puzzle: Find the Image Location and Size

[lilkrazyrae]

A converging lens has a focal length of 25cm. A 1.00cm tall object is placed 15.0cm in front of the lens. Find the image location and size, and describe it. Draw a ray diagram.

Ok so I get 1/p + 1/q = 1/f rearranged for q=pf/p-f which equals -37.5, so the object is 37.5cm behind the lens. and then m=-q/p=2.50cm. The h'=mh(i)=2.50*1.00=2.50cm tall. This all works out

BUT the ray diagram doesn't make the image at 37.5cm behind the lens. Some one help please!

 

[mukundpa]

Did you learned the sign conventions? what is the sign of the object distance?

 

[Andrew Mason]

This is double posted. See: https://www.physicsforums.com/showthread.php?t=118823

AM