Mirrors Reflect Light

Light is a form of electromagnetic wave. For all practical purposes, it travels in straight lines. As a result, it casts sharp shadow of objects on its path and causes eclipses.
Smooth surfaces reflect light in such a way that; angle of incidence = angle of reflection
Mirrors form images due to reflection of light. The image formed by a plane mirror is always of the same size as that of the object, erect, virtual and laterally inverted.
Curved mirrors may be used to form real as well as virtual images.

There are two types of curved mirrors

(i)Concave and (ii) Convex.

The geometric center of the mirror is called the pole (P) of the mirror. The center of the sphere of which the mirror is a part is called the center of curvature (C) of the mirror. An axis passing through the pole and containing the center of curvature is called the principal axis of the mirror. The distance between the center of curvature and the pole of the mirror is called the radius of curvature (r) of the mirror.
A set of parallel rays which are parallel to the principal axis after reflection from the concave mirror coverage to a point on the principal axis, or appear to diverge from a point on the principal axis on the other side of the mirror in the case of a convex mirror. The point is called the principal focus (f) of the mirror. The distance between the principal focus and the pole of the mirror is called the focal length (f) of the mirror.

The image formed by a curved mirror when an object is placed in front of it may be located using two of the following three rays of light:
(i) A ray of light parallel to the principal axis after reflection passes through the principal focus.
(ii) A ray of light passing through the principal focus after reflection goes parallel to the principal axis.
(iii) A ray incident normal to the mirror, after reflection retraces its paths and passes through the centre of curvature. When two reflected rays meet or appear to meet corresponds to one end of the image.

In the case of a Concave mirror, when the object is placed between F and P, a magnified, erect and virtual image is formed behind the mirror.

When the object is at F, the reflected rays are parallel to each other, and so the image is formed at infinity.

When the object is between C and F, a real, inverted and magnified image is formed beyond C.

When object is at C, a real inverted image which is of the same size as that of the object is formed at C itself.


When the object is placed beyond C, a real, diminished and inverted image is formed between C and F.

Rays coming from different objects are parallel to each other. Therefore, images of different objects are formed at the focal plane of the Concave mirror.

In the case of a convex mirror; irrespective of the position of the object, a virtual, diminished and erect image is formed behind the mirror. The nature of reflection from a convex mirror allows a large field of view.

When an object is placed at a distance of u, from a mirror of a focal length, f and if the image is formed at a distance v from the mirror,