Question

S
Problem-2 : The focal length of a concave mirror
is 30 cm. Find the position of the object in front of
the mirror so that the image is three times the size of
the object.
Sol.​

Answer 1

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.

Explanation:

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