. A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find


A lens forms the image of an object placed at a distance 15 cm from it, at a distance 60 cm in front of it. Find: (i) the focal length, (ii) the magnification, and (iii) the nature of image.

 

Best Answer

Given,

Object distance, u = – 15 cm

Image distance, v = – 60 cm

(i) Lens formula is,

1 / v – 1 / u = 1 / f

∴ 1 / – 60 – 1 / – 15 = 1 / f

∴ 1 / f = 1 / 15 – 1 / 60

∴ 1 / f = 3 / 60

∴ f = 60 / 3

∴ f = 20 cm

For a lens, magnification is

m = v / u

∴ m = – 60 / – 15

∴ m = +4

(iii) The nature of the image is erect, virtual and magnified.

 

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