Question

An object is kept in front of a concave mirror of focal length 20 cm. The image is three times the size of the object. Calculate two possible distances of the object from the mirror.

Answer 1

m=I/O...(I is the size of image.....and O is the size of object)
=} given...image= 3 times size of object
=}I=3O
value of m= I/O=3O/O= 3/1
and m is also equal to -(v/u)
where v is the distance of image and u is the distance. of object)
so, -3/1= -(v/-u)
-3u=v
so according to formula...1/f=1/u+1/v
-1/20=1/u-1/3u
-1/20=2/3u
-40/3=u

so object is 40/3 cm in front of the mirror.....
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