Question

A concave mirror has a focal length of $ 5\,cm $ . When an object is placed at a distance of $ 15 \,cm $ from the mirror, where is the image formed?

• A. 10 cm in front of the mirror
• B. 7.5 cm behind the mirror
• C. 2.5 cm in front of the mirror
• D. 7.5 cm in front of the mirror

Answer 1

Answer: (D)

Here, $f=-5\, cm$
$u=-15 \,cm $
$v=?$
From the mirror formula $\frac{1}{f}=\frac{1}{y}+\frac{1}{v}$
$\frac{1}{-15}+\frac{1}{v}=-\frac{1}{5}$
$\frac{1}{v}=\frac{1}{-5}+\frac{1}{15} $
$v=-7.5 \,m$
The image is formed at $7.5\, cm$ in front of the mirror.