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 10 mm long awl pin is placed vertically in front of a concave mirror

Q. 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:  -20 cm

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