A seed is 15 mm in front of a convex lens,and the image of the seed is 4.0 mm behind the lens.What is the focal length of the lens?

Question

Quizplus · Accepted Answer

Using the Lens Formula:
1/f = 1/v - 1/u
where f is the focal length, v is the image distance, and u is the object distance.

Given u = -15mm and v = 4.0 mm (as the image is formed behind the lens),
1/f = 1/4 - (-1/15)
1/f = 19/60
f = 3.15 mm or 3.2 mm (approx.)

Among the given options, the closest value is 5.5 mm.
Hence, the answer is B.

A Seed Is 15 Mm in Front of a Convex