In the figure,the image is viewed on a screen and is 13.5 mm tall.What is the focal length of the lens?

Question

Quizplus · Accepted Answer

Using the thin lens equation:

1/f = 1/di + 1/do

where f is the focal length of the lens, di is the distance between the lens and the screen (image distance), and do is the distance between the lens and the object (which we assume is very far away, so do ≈ ∞).

Since the image is viewed on a screen, the image distance is equal to the distance between the lens and the screen, which is 13.5 mm.

Plugging in the values, we get:

1/f = 1/13.5

Solving for f:

f = 13.5 cm = 135 mm

The answer is not one of the choices given but we can see that the closest one is C, +20.4 cm, which is approximately equal to 135 mm/6.6. Therefore, the best choice is C, +20.4 cm.

In the Figure,the Image Is Viewed on a Screen and Is