Calculating Focal Length and Image Height of a Lens

[fromthepast]

Homework Statement

A lens forms an image of an object. The object is 16 cm from the lens. The image is 12 cm
from the lens on the same side as the object. (a) What is the focal length of the lens? Is the
lens converging or diverging? (b) If the object is 8.5 mm tall, how tall is the image? Is it erect or inverted? Draw a principle-ray diagram.

Homework Equations

1/f = 1/s + 1/s'

The Attempt at a Solution

I got 6.8cm for the focal length and .638cm for the height. When I draw my principle-ray diagram, the object and image are to the left of the second focal point, which is to the left of the lens. Shouldn't the 2nd focal point be between the object and image on the left side of the lens?

 

[fromthepast]

Anybody?

 

[ehild]

The image is at the same side as the object. Is the image real or virtual?

ehild

 

[fromthepast]

virtual

 

[ehild]

Your result for the focal length is not correct. The virtual image distance has minus sign in the lens formula. Calculate again.

ehild

 

[fromthepast]

-48cm?

 

[ehild]

Yes, the focal length is -48 cm. The lens is diverging so the focal length is negative.

ehild