Question

A $4.5cm$ object is placed perpendicular to the axis of a convex mirror of focal length $15cm$ at a distance of $12cm$ . The size of the image is

• A. 6.0 cm
• B. 4.5 cm
• C. 3.0 cm
• D. 2.5 cm

Answer 1

Answer: (D)

Here, $u=-12cm,f=15cm$
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$\frac{1}{v}=\frac{1}{f}-\frac{1}{u}$
$\frac{1}{v}=\frac{1}{15}+\frac{1}{12}$
$\frac{1}{v}=\frac{5+4}{60}$
$v=\frac{60}{9}cm$
Now,
$\frac{I}{O}=\frac{u}{v}$
$\frac{4.5}{O}=\frac{12}{60/9}$
Length of object
$=\frac{4.5\times 5}{9}=2.5cm$