# A converging lens of focal length f = 8.96 cm forms a sharp image for two positions of the lens

aeroboi
Homework Statement:
The distance between an object and its image is fixed at 40.0 cm. A converging lens of focal length f = 8.96 cm forms a sharp image for two positions of the lens. What is the distance between these two positions?
Relevant Equations:
f=(s*s')/(s+s')
s'=(sf)/(s-f)
I am aware that the object would be to the left of the lens and the image would be to the right, but I don't understand what it is mean by " A converging lens of focal length f = 8.96 cm forms a sharp image for two positions of the lens." I don't understand where the two positions would be and why two positions are produced.

I'd appreciate any help visualizing this and a push for an approach. Thanks!

Homework Helper
Gold Member
It means that if you fix the distance between the object and the image (##s+s'##) there are two possible choices for the values of ##s## and ##s'##.

aeroboi
It means that if you fix the distance between the object and the image (##s+s'##) there are two possible choices for the values of ##s## and ##s'##.
Ok... but isn't that distance just 40cm (as stated in the problem statement)?