Question

Ryan Bologna has a lens of unknown focal length which produces an image with an image distance of -5.0 cm.  What is the unknown focal length if the object is 10.0 cm from the lens?  What kind of lens is this?

Answer 1

Answer

By lens formula

$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$

$\frac{1}{f}=\frac{1}{10.0}+\frac{1}{-5.0}=-10m$

Focal length is negetive so it is concave lenses or diverging lense.