A spherical mirror forms diminished virtual image of magnification 1 / 3. Focal length is 18 cm. The distance of the object is

Question

A spherical mirror forms diminished virtual image of magnification 1 / 3. Focal length is 18 cm. The distance of the object is (A) 18 cm (B) -36 cm (C) 48 cm (D) infinite

Tardigrade Admin · Accepted Answer

Clearly, the given mirror is a convex mirror. As m=(f/f-u) ⇒ (1/3)=(18/18-u) or 3 × 18=18-u or u=-2 × 18 cm or u=-36 cm

Q. A spherical mirror forms diminished virtual image of magnification $1/3$ . Focal length is $18 c m$ . The distance of the object is

18 cm

-36 cm

48 cm

infinite

Clearly, the given mirror is a convex mirror.
As $m = \frac{f}{f - u}$
$\Rightarrow \frac{1}{3} = \frac{18}{18 - u}$
or $3 \times 18 = 18 - u$
or $u = - 2 \times 18 c m$
or $u = - 36 c m$

Q. A spherical mirror forms diminished virtual image of magnification 1/3. Focal length is 18cm. The distance of the object is