Find the focal length of a diffusing (biconcave) lens if the distance from the lens to the object is 12 cm

Find the focal length of a diffusing (biconcave) lens if the distance from the lens to the object is 12 cm, and to the image is 5.5 cm.

To solve the problem, we use the formula:

1 / V + 1 / U = 1 / F, where:

U is the distance from the lens to the object, cm;

V is the distance from the lens to the image.

Accordingly, F = 1 / ((1 / V) + (1 / F)).

We decide:

F = 1 / ((1/12) + (1 / 5.5)) = 1 / 0.265151515 ~ 3.77 cm.

Answer: The focal length of the diffusing lens is ~ 3.77 cm.