The inside portion of part of a hollow metal sphere of diameter 20cm is polished. The portion will therefore form a
A
concave mirror of focal length 5cm
B
concave mirror of focal length 10cm
C
convex mirror of focal length 5cm
D
convex mirror of focal length 20cm
Verified Correct Answer: A.
Step-by-Step Mathematical Solution
Since diameter of the sphere = 20cm, then, the radius of curvature = 10cm
Focal length, f = \(\frac{R}{2} = \frac{10}{2}\) = 5cm
The inside of a hollow metal sphere forms a concave mirror.
Source: Myschool Past Questions Archive (Record #588)