Where should an object be placed in front of a concave mirror of focal length 20cm so as to obtain a two times magnified virtual image of the object
Answers
Answered by
57
Explanation:
let u be the distance of object fro. the mirror.
f=20cm
m(magnification)=2
since m=-v/u
therefore
v=-2u
now putting values in formula
1/v + 1/u=1/f
-1/2u + 1/u=1/20
therefore
1/2u=1/20
1/u=1/10
u=10cm
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Answered by
2
Since it is 2 times magnified, m = -2
so -v/u = -2
similarly, 1/v + 1/u = 1/f
so 1/v + 1/u = 1/-20
-v/v + -v/u = -v/-20 (multiply throughout by -v)
-1 -2 = v/20
-3 = v/20
v = -60
-2 = -v/u
-2 = 60/u
u = -30
so the object must be placed 30 cm from the mirror.
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