The focal length of a concave mirror is 30cm.Find the position of the object in the front of the mirror so that the image formed is 3 times the size of the object.
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Answer:
1/v + 1/u = 1/f
Let the image be real. v is -ve. u is -ve. f is -ve.
v = 3 u as magnification m = -v / -u = v/u
1/(-3u) + 1/(-u) = 1/(-f)
-4/3u = 1/(-30) => u = 40 cm that is 40 cm infront of the mirror.
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Let the image be virtual. so v/u = -3
v is +ve u is -ve f is -ve
v = 3u
1/3u - 1/u = -1/f
-2/3 u = -1/30 u = 20 cm that is 20 cm in front of mirror.
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