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 10cm

Correct answer is C

Concave Mirror: It is a spherical mirror whose outer surface is polished and inner or concave side is reflecting surface.

Convex Mirror: It is a spherical mirror whose inner surface is polished and outer side or convex side is the reflecting surface.

f = \(\frac{m}{4}\) = f = \(\frac{d}{4}\)

f = \(\frac{20}{4}\) = 5cm