Question

An object, located 80.0 cm from a concave lens, forms an image 39.6 cm from the lens on the same side as the object. What is the focal length of the lens?

Answer 1

-78.4 cm

Step-by-step explanation:

We can solve the problem by using the lens equation:

`(1)/(f)=(1)/(p)+(1)/(q)`

where

p is the distance of the object from the lens

q is the distance of the image from the lens

f is the focal length

Here we have

p = 80.0 cm

q = -39.6 cm (negative, because the image is on the same side as the object , so it is a virtual image)

Substituting, we find f:

`(1)/(f)=(1)/(80.0 cm)+(1)/(-39.6 cm)=-0.0128 cm^(-1)`

`f=(1)/(0.0128 cm^(-1))=-78.4 cm`