Question

a concave lens of focal length 20 cm forms an image at 15 cm how far is the object placed form the lens

Answer 1

Answer:

Explanation:

Given f = - 20 cm, (sign convention) , v = - 10 cm

(∴ image formed by concave lens is virtual)

By using lens formula,  

or u = - 20  

Thus the object is placed at 20 cm from the concave lens  

   

Answer 2

Answer:

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