Question

A lens form the image twice of its size ad real and inverted which focal length is 15 cm .Find the position and nature of the image formed

Answer 1

Consider variables u = object distance, v= image distance



Consider variables u = object distance (in cm), v= image distance (in cm)

Given,

-u + v = 100 ......eq (1)

Magnification = v /u = -3 (real and inverted image)

                  v = -3u ........eq (2)

Focal length 1/f = 1/v - 1/u  ......eq (3)

Substitute eq (2) in eq (1), we get u = -25 cm

eq (2) v = -3 u = - 3 *- 25 = 75 cm

Substitute eq (2) in eq (3), we get  f = - 3 u/4  = -3 * -25/4 = 18.75 cm.

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