A man has a concave shaving mirror or focal length 0.2 m. How far should the mirror be held from his face in order to give an image of two fold magnification?

Question

A man has a concave shaving mirror or focal length 0.2 m. How far should the mirror be held from his face in order to give an image of two fold magnification? (A) -0.1 m (B) 0.2 m (C) 0.3 m (D) 0.4 m

Tardigrade Admin · Accepted Answer

As, m =(f/f-u) ⇒ 2=(-0.2/-0.2-u) or 2=(0.2/0.2+u) or 0.4+2 u=0.2 Or 2 u=0.2-0.4=-0.2 Or u=-0.1 m

Q. A man has a concave shaving mirror or focal length $0.2 m$ . How far should the mirror be held from his face in order to give an image of two fold magnification?

-0.1 m

0.2 m

0.3 m

0.4 m

As, $m = \frac{f}{f - u}$
$\Rightarrow 2 = \frac{- 0.2}{- 0.2 - u}$
or $2 = \frac{0.2}{0.2 + u}$
or $0.4 + 2 u = 0.2$
Or $2 u = 0.2 - 0.4 = - 0.2$
Or $u = - 0.1 m$

Q. A man has a concave shaving mirror or focal length 0.2m. How far should the mirror be held from his face in order to give an image of two fold magnification?