Question

an object is placed at 60 cm from a concave lens. The image is formed at a distance of 20 cm from the optical center. Find the focal length of the lens? Is the lens coverging or diverging?
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Answer 1

Since the lens is concave the object distance and the image distance, both will be negative.

Given that:

u = -60 cm

v = -20 cm

We know that:

1/f = 1/v - 1/u

=> 1/f = -1/20 + 1/60

=> 1/f = (-3+1)/60

=> 1/f = -2/60

=> 1/f = -1/15

Thus, f = -15 cm

Since the lens if concave, it is a diverging lens

Thanks!

Answer 2

Answer:

your answer is -15......