Question

An object is placed in front of a concave mirror of focal length20cm . The image formed is three times the size of the object . Calculate two possible distances of the object from the mirror .

Class - 10th
Chapter - Light , reflection and refraction .

Kindly don't spam ​

Answer 1

$\huge{\blue{\fcolorbox{blue}{lime}{\boxed{\orange{\bf{\underbrace{\overbrace{\fcolorbox{blue}{black}{\underline{\blue{《Answer\: : 》}}}}}}}}}}}$

Hope it helps you...

━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Answer 2

Given:-

Focal length of concave mirror, f = 20cm

And, the image formed is three times the object,

∴ m = 3

To find:-

u, distance of object from the mirror

Solution:-

We have, m = 3

⇒ $\frac{-v}{u} =3$

⇒ -v = 3u

⇒ v = -3u

Now, from mirror formula,

$\frac{1}{v}+\frac{1}{u} =\frac{1}{20}$                                                               (∵f = 20cm)

⇒ $\frac{1}{-3u} +\frac{1}{u} = \frac{1}{20}$

⇒ $\frac{-1+3}{3u} =\frac{1}{20}$

⇒ $\frac{2}{3u} =\frac{1}{20}$

⇒ 3u = 2×20

⇒3u = 40

⇒ u = $\frac{40}{3}$

Hence, the distance of the object from the mirror, u = 40/3 cm