The inside portion of a hollow metal sphere of diameter 20 cm is polished. The portion will therefore form a
A
Concave mirror of focal length 5cm.
B
Concave mirror of focal length 10 cm.
C
Convex mirror of focal length 10 cm
D
Convex mirror of focal length 5cm
Verified Correct Answer: A.
Physical Principles & Numerical Solution
Diameter = 20cm
The radius of curvature, R = 10cm
But, focal length, f = \(\frac{R}{2} = \frac{10}{2}\) = 5 cm.
Because the inside portion is polished, light reflects off the hollow, caved-in interior. A mirror that reflects light from its inner surface is concave.
Source: WAEC / JAMB / NECO Classroom Archive (Record #72066)