Question

Reena and Vani find a discarded plastic lens lying on the beach. The girls discuss
what they learnt in Physics and argue whether the lens is a converging or diverging
one. When they look through the lens, they notice that the objects are inverted, If an object 25 cm in front of the lens forms an image 20 cm behind the lens,
what is the focal length of the lens?

Answer 1

Explanation:

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Answer 2

Answer:

11.1cm

Explanation:

Length of the Object = (u) = -25 cm  (Given)

Length of the Image = (v) = +20 cm  (Given)

According to the lens formula,

1/v - 1/u = 1/f

1/20 - 1/-25 = 1/f

1/f = 1/20 + 1/25

1/f = 500/45

f = 11.1

Thus, the focal length of the length is 11.1cm

Since the lens focal length is positive and the image created is reversed, we may assume that the lens is either a convex lens or a converging lens.