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:
[tex]\frac{1}{q}=\frac{1}{f}-\frac{1}{p}=\frac{1}{20 cm}-\frac{1}{40 cm}=\frac{1}{40 cm}\\q = 40 cm[/tex]
