An object is placed at a distance of 18 cm in front of a mirror. If the image is formed at a distance of 4…
An object is placed at a distance of 18 cm in front of a mirror. If the image is formed at a distance of 4 cm on the other side, then focal length, nature of the mirror and nature of image are respectively
3.14 cm , concave mirror and real image
3.14 cm , convex mirror and real image
5.14 cm , convex mirror and virtual image
5.14 cm , concave mirror and virtual image
Solution
For a spherical mirror,
$\mathrm{u}=-18 \mathrm{~cm}, \mathrm{v}=4 \mathrm{~cm}$
$\therefore$ By mirror formula,
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}=\frac{1}{4}+\frac{1}{-18} \Rightarrow f=\frac{36}{7} \mathrm{~cm}=5.14 \mathrm{~cm}$ Also, $\mathrm{f}=+\mathrm{ve}$. So, mirror is convex and virtual image is formed.