Question

A concave
lens of focal length 20cm forms
an image is em from the lens. How far is
the object placed from the dens ? Draw the ray
diagram.​

Answer 1

Step by step explanation:

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

(∴ image formed by concave lens is virtual)

Using mirror formula:

=> -1/u + 1/v = 1/f

=> -1/u - 1/10 = -1/20

=> -1/u = -1/20 + 1/10

=> -1/u = 1/20

=> u = -20

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

Ray Diagram: Please refer to the image attached above.

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