Question

the image of an extended object placed in front of a concave mirror is formed at a distance of 40 cm from the object if the image is 3 times bigger than the object the magnitude of focal length of mirror is

Answer 1

Answer:

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Answer 2

Answer:

15cm

Explanation:

Let object distance be u, image distance be v and focal length be f.

The distance between the image and object is = 40 cm

u – v = 40   --(1)

The real image is 3 times bigger than the object, so, magnification,

m = -v/u = -3

v = 3u   --(2)

from (1) and (2)

u = -20 cm

So, v = -60 cm

Now, 1/f = 1/v + 1/u

1/f = -1/60 – 1/20

f = -15 cm

focal length of the mirror is 15 cm.