Question

An object is placed somewhere in front of concave mirror. The focal length of the mirror is $10.0cm$. The image for this object CANNOT be formed in which of the following locations?

• A. $25.0cm$ in front of the mirror
• B. $20.0cm$ in front of the mirror
• C. $15.0cm$ in front of the mirror
• D. $5.0cm$ in front of the mirror
• E. $10.0cm$ behind the mirror

Answer 1

The correct option is D $5.0cm$ in front of the mirror

Given : $f=-10$ cm

Let the object is placed at a distance $x$ from the pole of mirror i.e $u=-x$.

Using mirror formula : $\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

$\therefore$ $\frac{1}{v}+\frac{1}{-x}=\frac{1}{-10}$ $⟹v=\frac{10x}{10-x}$

For option D : $v=-5.0$ cm

$\therefore$ $-5.0=\frac{10x}{10-x}$ $⟹x=-10$ cm (not possible)

Hence option D is correct.