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The focal length of the concave mirror is 30cm.find the position of the object in front of the mirror so that the image is 3 times the size of the object

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by vickyjangam5

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by vickyjangam5

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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.

v = 3 u as magnification m = -v / -u = v/u

1/(-3u) + 1/(-u) = 1/(-f)

-4/3u = 1/(-30) =>

===========================================

Let the image be virtual.

v is +ve u is -ve f is -ve

v = 3u

1/3u - 1/u = -1/f

-2/3 u = -1/30