Question

A square of side 3 cm is located at a distance 25 cm from a concave mirror of focal length 10 cm. The centre of square is at the axis of the mirror and the plane is normal to axis of mirror. The area enclosed by the image of the square is

• A. $4\, cm^2$
• B. $6\, cm^2$
• C. $16\, cm^2$
• D. $36\, cm^2$

Answer 1

Answer: (A)

$4\, cm^2$

Answer 2

Linear magnification, $m = \frac{I}{O}=\frac{f}{u-f}$ $= \frac{10}{25-10}$ $m = \frac{10}{15}=\frac{2}{3}$ Areal magnification $=m^2 = \frac{4}{9}$ $$ Area of image $= \frac{4}{9} \times$ area of object $= \frac{4}{9} \times (3)^2 = 4\, cm^2$