Question

A square wire of side 3.0 cm is placed 25 cm infront of concave mirror of focal length 10 cm with its centre on the axis of the mirror and its plane normal to the axis. The area enclosed by the image of the wire is –

• A. 7.5 cm²
• B. 6.0 cm²
• C. 4.0 cm²
• D. 3.0 cm²

Answer 1

Answer: (C)

4.0 cm²

Answer 2

Area of image = m² × A₀

= $\left( \frac { f } { f - u } \right) ^ { 2 }$ × 3² = $\left( \frac { - 10 } { - 10 + 25 } \right) ^ { 2 }$ × 9 cm²

= $\frac { 4 } { 9 }$ × 9cm² = 4.0 cm²