# Draw a ray diagram

1. Apr 26, 2006

### 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 doesnt make the image at 37.5cm behind the lens. Some one help please!

Sorry to double post but I thought maybe someone here could help me!

2. Apr 26, 2006

### Andrew Mason

The - sign means that the image is not behind the lens. When the object is inside the focal length you get a virtual image. A virtual image appears to be an image on the same side as the object.

The rays through the lens do not converge on the other side. Project the rays back in front of the lens. They will converge on the virtual image which you can see by looking back through the lens toward the object.

AM