Question

An object placed 91 cm in front of a converging lens forms an image 22 cm behind the lens. What is the focal length of the lens?

Answer 1

29.01 cm

Step-by-step explanation

Given:

• The distance from the object to a converging (convex) lens, do = -91 cm

,

• The distance from the image to the lens, di = 22 cm

Find:

• The focal length of the lens, f

The image is behind the lens, so its distance to the lens is positive while the distance from the object to the lens is negative. Using the lens equation,

`(1)/(f)=(1)/(d_o)+(1)/(d_i)`

We can find the focal length,

`f=(1)/((1)/(d_o)+(1)/(d_i))=(1)/((1)/(-91cm)+(1)/(22cm))\approx29.01cm`

Hence, the focal length of the lens is 29.01 cm.