Question

A lens of focal length 15 cm forms an erect image three times the size of the object. The distance between the object and image is:; (a) 20 cm (b) 16 cm; (c) 24 cm (d) 36 cm

Answer 1

Answer:

The correct answer will be option a 20 cm

Explanation:

According to the problem the focal length, l is 15 cm

which forms the image three times larger i.e magnification,m = 3

let the object distance is d and image distance is u

we know that

m = u/d

=> 3= u/d

=>u= 3d

The formula to find the distance:

1/u- 1/d= 1/l

1/3d- 1/d= 1/15

=> 3d= - 30

=>d = -10

now u= 3d

         = 3 x (-10)

          = -30

Therefore the distance between the image and object is (30 -10)= 20 cm

Answer 2

Explanation:

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