Spherical Mirrors

We use mirrors every day.

We use them to dress up and to do make up. We look at our own image and correct ourselves.

Basically, any shiny surface can form an image but plane mirrors are capable of forming an image identical to the object in front of it.

Let us have a brief overview of how we see an image in a plane mirror, and then go to other types of mirrors.

Image in a plane mirror

A plane mirror is one whose surface is so smooth that it projects images of objects placed in front of it.

The plane mirror produces an image of the object on the opposite side of the mirror

The distance from the object to the mirror equals the distance from the image to the mirror.

And to add it all, the image formed by a plane mirror is virtual, upright, and of the same shape and size as the object that the mirror is reflecting.

The images that can be captured on a screen like a projector are called REAL images. The images that cannot be capture like the images in a mirror are called VIRTUAL images.

Now let's see other types of mirrors. They have a spherically curved surface. There are two types of spherical mirrors as shown above.

Let us now see how a spherical mirror is constructed.

All types of spherical mirrors are formed by cutting a small fragment of a section of a sphere.

Every sphere has a radius and a center. The radius is called RADIUS OF CURVATURE and the center is called CENTER OF CURVATURE.

The point in the middle P as shown above is called POLE. The line passing through the center of curvature and the pole is called PRINCIPAL AXIS.

The length CP will be the same as the radius. The mid point of the line segment CP is called Focal point(F). The length CF = PF is called FOCAL LENGTH.

If the outer part of the spherical fragment is polished, it is called a concave mirror

If the inner part of the spherical fragment is polished it is called a convex mirror.

In the concave mirror, the inner surface reflects light whereas in the convex mirror the outer surface does.

Concave mirror is called a converging mirror because it converges the light rays to a point after reflection.

Whereas a Convex mirror is called a diverging mirror because it diverges the light rays after reflection.

Revision

All types of spherical mirrors are formed by cutting a small fragment of a section of a sphere.

In the concave mirror, the inner surface reflects light whereas in the convex mirror the outer surface does.

Concave mirror is called a converging mirror because it converges the light rays to a point after reflection.

Whereas a Convex mirror is called a diverging mirror because it diverges the light rays after reflection.

The centre of the sphere of which the spherical mirror is a fragment of is called the Centre of Curvature.

The radius of the sphere, of which the mirror is a part is called the Radius of Curvature for the mirror.

A line going through the center of the mirror, which is perpendicular to the mirror surface is the Principal Axis.

The point on the mirror where the principal axis intersects is called the pole.

The End