Question

A physics book is located $25.0cm$ in front of a convex mirror. The (virtual) focal length of the mirror is $20.0cm$.
Where is the image of the book formed, relative to the mirror?

• A. $100.0cm$ in front of the mirror
• B. $11.1cm$ in back of the mirror
• C. $5.0cm$ in front of the mirror
• D. $100.0cm$ in back of the mirror
• E. $11.1cm$ in front of the mirror

Answer 1

The correct option is B $11.1cm$ in back of the mirror

Given : $u=-25.0$ cm $f=20.0$ cm

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

$\therefore$ $\frac{1}{v}+\frac{1}{-25.0}=\frac{1}{20.0}$ $⟹$ $v=+11.1$ cm

Thus image is formed at $11.1$ cm behind the mirror.