A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is
A. -30 cm
B. -20 cm
C. -40cm
D. -60 cm
Answer:B
A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is
A. -30 cm B. -20 cm C. -40cm D. -60 cm