An object is kept in front of a concave mirror of focal length 15 cm. The image formed is real and three times the size of the object. Calculate the distance of the object from the mirror.

 

Answers (1)
S safeer

Given that ; f = 15 cm

                   m = +3 (magnification)

                   u = ?

Now, calculating the distance of the object from the mirror (u),

we know, the mirror formula;

\frac{1}{v}+\frac{1}{u}=\frac{1}{f}

Here, m=+3,f=-15\: cm

m=\frac{v}{u}=3\; \; \; \; \therefore v =3u

\frac{1}{f}=\frac{1}{v}+\frac{1}{u}

\frac{1}{-15}=\frac{1}{3u}+\frac{1}{u}

u = -20\; cm

Hence, (u) = 20 is the distance of the object from the mirror.

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