Mirror and its Types

Spherical Mirrors:

On the basis of the direction of curvature there are two types of spherical mirrors.

  • Concave mirrors:A concave mirror is the spherical mirror in which light is reflected from the concave surface or bent in surface.
  • Convex mirrors: A convex mirror is a spherical mirror in which light is reflected from the spherical surface which is outward in curvature or bulged outwards.

Before going to study the images formed by spherical mirrors, we have to study the basic geometrical terms related to spherical mirrors as discussed below

(a) Pole of the spherical mirror:

Pole of the spherical mirror is the center point on the reflecting surface of spherical mirror.

It is denoted by P.

(b) Center of curvature of the spherical mirror:

The spherical reflecting surface has its own center i.e. center of sphere which is called as center of curvature of spherical mirror.

It is denoted by C.

In case of concave mirror it lies towards the reflecting surface.

In case of convex mirror it lies opposite to the reflecting side of spherical mirror.

(c) Radius of curvature of spherical mirror:

Radius of curvature is the radius of spherical reflecting surface forming the spherical mirror.

It is denoted by R.

(d) Principal axis of spherical mirror:

The line joining the distance between the pole and the center of curvature of spherical mirror is called as principal axis of spherical mirror.

Principal axis is always perpendicular to the spherical mirror at its pole.

(e) Principal focus or Focal point of the spherical mirror:

Consider the parallel beam of light is incident on the reflecting surface of a concave mirror as shown in fig

After reflecting from the concave surface, all this rays meet at a same point on the principal axis. The point at which all the rays meet on the principal axis is called as principal focus or focal point of the concave mirror.

Similarly, in case of convex mirror, the reflected rays coming from reflecting surface of convex mirror are appears to come from a common point behind the reflecting surface on principal axis as shown in fig

This common point on principal axis is called as principal focus or focal point of the convex mirror.

The principal focus or focal point is represented by F.

a) Concave mirror                                    b) Convex mirror

f) Focal length of the spherical mirror:

The distance between the principal focus and the pole of the mirror is called as the focal length of the spherical mirror.

It is denoted by f.

g) Aperture of the spherical mirror:

The diameter of the reflecting surface of spherical mirror is called as aperture of spherical mirror.

In fig. XY represents the aperture of spherical mirror.

The spherical mirrors having radius of curvature greater than aperture shall considered for study.

R=2f represents the relation between radius of curvature and focal length.

It concludes that focal point is the center or midpoint of the radius of curvature of spherical mirror.

Questions:

  • What are difference and similar points in case of concave & convex mirrors?
  • What is mean by virtual image & real image?
  • The reflection of light depends on which properties of the spherical mirrors?
  • Have you observed which mirrors are we using in daily life & for what kind of purpose we are using them?

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