Final answer:
A candle placed 20 cm from a concave mirror with a focal length of 10 cm will form a real, inverted, and reduced image between the focal point and the center of curvature.
Step-by-step explanation:
When a candle is placed on the principal axis of a concave mirror at a distance of 20 cm and the focal length of the mirror is 10 cm, we can determine the nature of the image formed by using the mirror equation:
1/f = 1/do + 1/di
Where f is the focal length, do is the object distance, and di is the image distance. Since the object is placed beyond the focal point, the rays after reflection from the mirror will converge to form a real, inverted, and reduced image on the same side as the object. This type of image can be projected onto a screen and is located between the focal point and the center of curvature of the mirror.