Question

if a magnification of -1 is to be obtained using a concave mirror of a focal length 6 cm, then what should be the position of object​

Answer 1

magnification "m"=-2times. 40+2u=-20. so if you object be placed at the distance of 30 cm then the two times magnified image will be obtain.

Answer 2

Given:

Required magnification, $m=-1$

Focal length of the mirror, $f=-6cm$

To Find:
Position of the object

Solution:

Let us assume the object is placed at a distance, $u$ from the mirror such that the image is formed at a distance of $v$.

Now, in case of mirrors,

    $m=-\frac{v}{u}$

⇒ $-1=-\frac{v}{u}$

⇒  $u=v$

Using mirror formula,

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

⇒ $\frac{1}{u} +\frac{1}{u} =-\frac{1}{6}$

⇒ $\frac{2}{u} =-\frac{1}{6}$

⇒ $u=-12cm$

Hence, the object must be placed 12cm in front of the mirror.