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
- – 30 cm
- – 20 cm
- – 40 cm
- – 60 cm
Here, size of object = O = + 10.0 mm = + 1.0 cm (as, 1 cm = 10 mm)
Size of Image size = I = 5.0 mm = 0.5 cm
Image distance, v = − 30 cm (as image is real)
Let, object distance = u
Focal length, f =?
The correct option is B.