Question

A square wire of side 3.0 cm is placed 25 cm away from a concave mirror of focal length 10 cm. What is the area enclosed by the image of the wire? (The square wire is placed such that the centre of the wire on the axis of the mirror with its two sides normals to the axis):

• A. 4.0 cm2
• B. 4.5 cm2
• C. 9.0 cm2
• D. 20.25 cm2

Answer 1

Answer: (A)

4.0 cm2

Answer 2

$\text{Magnification =}\frac{\text{size of image}}{\text{size of object}}$ Given, size of object = 3 cm $\text{Magnification}=\frac{f}{u-f}$ where, $f$ is focal length and u is object distance. $\therefore$ $m=\frac{10}{25-10}=\frac{10}{15}$ $\therefore$ Size of image $=m\times$ size of object $=\frac{10}{15}\times 3=2\,cm$ Area of image $={{(side)}^{2}}$ $={{(2)}^{2}}=4\,c{{m}^{2}}$