Question

An object is 40 cm in front of a convex lens with a focal length of 20 cm. What is the position of the image using ray tracing?

Answer 1

Answer:

40 cm behind the lens

Explanation:

Please refer to the attached picture for the ray tracing, where

f is the focal length

p is the location of the object

q is the location of the image

Each tick in the picture corresponds to 20 cm, so we can observe that

p = 40 cm

f = 20 cm

q = 40 cm

Also, q is inverted, real and same size as the object.

The location of the image, q, can also be verified by using the lens equation:

$\frac{1}{q}=\frac{1}{f}-\frac{1}{p}=\frac{1}{20 cm}-\frac{1}{40 cm}=\frac{1}{40 cm}\\q = 40 cm$