a concave mirror of focal length 18 cm forms an erect image, three times the size of the object. how far is the object from the mirror?
singnarsingh:
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given concave mirror
magnification = +3 (since the object is erect)
f = -18 (since focal length of concave mirror is negative)
u =?
m = -(f/u-f)
m = -(-18/u-(-18) )
3 = - ( -18/u+18 )
3 = 18/u+18
3(u+18) = 18
3u + 54 = 18
3u = 18-54
3u = -36
u = -12
the object is 12 cm far from mirror
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