Question

7. An object of 6 cm height is placed at a distance of 8 cm from a
converging mirror. It produces an erect image of size 9 cm. Find the
focal length of the mirror.
​

Answer 1

$\boxed{\bf{\blue{\implies Given:}}}$

• Concave mirror
• u = -8cm
• h = 6 cm
• h' = 9cm
• f = ?

$\boxed{\bf{\red{\implies Solution:}}}$

• Using magnification formula
• $m = - \frac{v}{u} = \frac{hi}{ho}$
• $m = \frac{9}{6} = 1.5$
• $1.5 = \frac{ - v}{ - 8}$
• $\boxed{\bf{v = 8 \times 1.5 = 12cm}}$
• Using Mirror formula

• $\frac{1}{f} = \frac{1}{v} + \frac{1}{u} = \frac{1}{12} - \frac{1}{8}$
• $\frac{1}{f} = \frac{ - 1}{24}$
• $\boxed{\bf{f = - 24cm}}$

$\boxed{\bf{\green{\implies Hope \: it \: helps! }}}$