Final answer:
The focal length of the mirror can be found using the formula 1/f = 1/do + 1/di. Given that the mirror forms an image twice as large as the object, with an object distance of 10 cm, the focal length is found to be 20 cm.
Step-by-step explanation:
The focal length of a mirror can be found using the formula:
1/f = 1/do + 1/di
Given that the image formed by the mirror is twice as large as the object and the object distance (do) is 10 cm, we can substitute the values into the formula:
1/f = 1/10 + 1/di
Since the image is twice as large as the object, the image distance (di) would be -20 cm. Substituting the values into the formula again:
1/f = 1/10 + 1/-20
Simplifying the equation gives:
1/f = 1/10 - 1/20
1/f = 2/20 - 1/20 = 1/20
Therefore, the focal length (f) of the mirror is 20 cm. Hence, the correct answer is c.