Acell phone is placed 25 cm in front of a diverging lens with focal length of magnitude 20 cm. how far is the image of this phone from the lens? a) 9 cm b) 20 cm c) 11 cm d) 100cm

option (c)

Explanation:

distance of object, u = - 25 cm

focal length, f = - 20 cm

Let the distance of image from the lens is v.

Use lens equation

1 / f = 1 / v - 1 / u

1 / (-20) = 1 / v + 1 / 25

- 1 / 20 - 1 / 25 = 1 / v

1 / v = (-25-20) / (20 x 25)

1 / v = - 45 / 500

v = - 500 / 45 = - 11.11 cm

v = 11 cm

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