posted by Bob .
A small statue has a height of 3.8 cm and is placed in front of a concave mirror. The image of the statue is inverted, 1.9 cm tall, and located 14 cm away from the mirror. Find the focal length of the mirror.
The image is real (because it is inverted)and the magnification is 1.9/3.8 = 1/2.
The image distance di is half the object distance do. (do = 2 di)
1/di + 1/do = 3/do = 1/f
f = do/3 = 2 di/3 = 9.33 cm
1/28 + 1/14 = 1/9.33