A concave lens produces an image 20 cm from the lens for an object placed 30 cm from the lens. Find the focal length of the lens.

Asked by Srishti Mallick | 4th Dec, 2013, 10:04: PM

Expert Answer:

For concave lens:
u = -30 cm, v = -20 cm (as it always forms a virtual image)
 
From the lens formula, we have
 

Answered by Romal Bhansali | 5th Dec, 2013, 09:37: AM

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