Question

A square wire of side 3cm is placed 25cm away from a concave mirror of focal length 10cm. What is the area enclosed by the image of the wire ? The centre of the square lies on the principal axis and perpendicular to the axis.

GIVE BRIEF EXPLANATION

Answer 1

u = -25 cm

f = - 10 cm

Using mirror formula,

1/f = 1/u + 1/v

-1/10 = -1/25 + 1/v

v = - 50/3

Magnification m,

m = - v/u = - [(-50/3)/(-25)] = -2/3

m = I/O = - 2/3

Length and breath both change in the same proportion.

Area of the object A_O = 3 x 3 = 9 cm²

A_I/A_O = (-2/3)²

A_I = (4/9) x 9 = 4 cm²