Question

The cut part of the sphere is coated outside with silver or similar material. What kind of mirror does it form?
A. Convex mirror
B. Concave mirror
C. Plane mirror
D. None

Answer 1

Hint: In order to solve this question we need to understand convex and concave mirrors. A convex mirror are those mirrors which are diverging in nature, when a parallel beam of light falls on a convex mirror then it would diverge that light such that it appears to come from a point known as focal point. Concave mirrors are those mirrors which are converging in nature, when a parallel beam of light falls on a concave mirror then it would converge that light such that it appears to come from a point known as focal point.

Complete answer:
When a sphere is cut at various angles, say from a diagonal or chord, then many curved surface forms. To make a mirror we must apply silver or any material on one side so that the parallel rays following on it do not get refracted and it only reflects from the surface opposite to coating.

When coating is done outside of a curved surface then parallel rays get reflected only from inside and due to geometry of that curved surface, rays converge to a point known as focal point, such curved surfaces or mirrors are known as concave mirrors.

So the correct option is B.

Note: It should be remembered that if the coating is done inside the curved surface then by geometry, it would diverge all rays falling on it, such that it appears to diverge from a point known as focal point, such a mirror is known as convex mirror. Concave mirror always forms an inverted image while convex forms the erect image.