Question

A luminous object is placed 20 cm from the surface of a convex mirror. A plane mirror is set so that the virtual images formed in the two mirrors coincide. If the plane mirror is at a distance of 12 cm from the object, then the focal length of the convex mirror is –

• A. 10 cm
• B. 5 cm
• C. 20 cm
• D. 40 cm

Answer 1

Answer: (B)

5 cm

Answer 2

u = – 20, v = 4 Ž $\frac { 1 } { \mathrm { f } }$ = – $\frac { 1 } { 20 }$ + $\frac { 1 } { 4 }$ Ž f = 5 cm