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
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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.
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