WAEC - Physics (2024 - No. 33)

The inside portion of a hollow metal sphere of diameter 20 cm is polished. The portion will therefore form a

Concave mirror of focal length 5cm.

Concave mirror of focal length 10 cm.

Convex mirror of focal length 10 cm

Convex mirror of focal length 5cm

Diameter = 20cm

The radius of curvature, R = 10cm

But, focal length, f = \(\frac{R}{2} = \frac{10}{2}\) = 5 cm.

When the inside portion of a hollow metal is polished, the outside is the reflecting surface. This forms a convex mirror.