What are Spherical Mirrors?

A Spherical Mirror is a mirror whose reflecting surface is curved, not straight. It may be curved either inwards, or outwards. In general, there are two types of spherical mirrors, namely, Concave Mirror and Convex Mirror.

Table of contents:

• ● What are concave mirrors
• ● What are convex mirrors
• ● Components of a spherical mirror

Concave Mirrors →❫

A spherical mirror, whose reflecting surface is curved inwards, is called a Concave Mirror.

Those type of mirrors converge light rays to a point. So, they are also known as converging mirrors.

A Concave Mirror

Dentists use concave mirrors to get a view of the inside condition of one's teeth. Solar coockers use concave mirrors to accumulate light at one point where we can place food for cooking.

Convex Mirrors →❪

A spherical mirror, whose reflecting surface is curved outwards, is called a Convex Mirror.

Light rays falling on a convex mirrors are diverged by the mirror; so, convex mirrors are also known as diverging mirrors.

A Convex Mirror

Convex mirrors are used in vehicles for getting the side-view. They are also used for security watch where large field of view is captured in the mirror.

Take the example of a spoon. The side of the spoon that holds food is similar to a concave mirror; the opposite side may be referred to as a convex mirror.

A spherical mirror, concave or convex, has different components like Pole, Principal Focus, Center of Curvature etc. Take a short tour with two different animations to identify them.

Components of a Spherical Mirror

Note : The following definitions are applicable to both concave and convex mirrors.

Center of Curvature :

A spherical mirror is a small part of a sphere. Obviously, it has a center. This center point is called the Center of Curvature (C) of the mirror. In case of a concave mirror, the reflecting side faces towards the Center of Curvature. For a convex mirror, the reflecting side faces opposite to the Center of Curvature.

Pole :

The centre or mid-point of the reflecting surface of a spherical mirror is known as the Pole (P) of the mirror.

Radius of Curvature :

We know that a spherical mirror is a small part of a sphere. The radius of that sphere is called the Radius of Curvature of the mirror.
It may also be defined as the distance between the Pole and the Center of Curvature of the mirror.

Principal Axis :

The imaginary line that connects the Center of Curvature and the Pole is known as the Principal Axis of the mirror.

Principal Focus (Focal point):

When parallel rays fall on the reflecting surface of a Concave mirror, reflection happens, and the reflected rays meet at a certain point. This point is known as the Principal Focus (F) of the mirror.

Note: For a convex mirror, reflected rays diverge, so virtual rays seem to meet at a point behind the mirror, which is the Principal Focus of the convex mirror. It is also known as the Focal Point of the mirror. Please check animations.

Focal Length :

The distance between the Principal Focus and the Pole of a spherical mirror is called the Focal Length (f) of the mirror.
Focal Length is actually half of the Radius of Curvature;
i.e., f   = ½ R  or,  R = 2f  

For reflection rules of concave and convex mirror, check the next page.

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