Plane Mirrors: Reflection and Image Formation

by Yuvi K - December 17, 2023

Introduction to Plane Mirrors

A plane mirror is a flat, smooth, highly reflective surface that forms an image of the object when light rays are incident upon its surface. These mirrors are made of glass or metal, and can produce a virtual, upright, and enlarged or diminished image depending on the distance of the object from the mirror. Plane mirrors are used for a variety of purposes such as in making ivories, medical imaging, astronomy, and consumer goods.

Reflection in Plane Mirrors

When light from an object is incident on a plane mirror, it is reflected by the mirror in the same direction as the incident light. This phenomenon of reflection is a physical property of light where the angle of incidence (कोण) equals the angle of reflection (वापसी कोण). In other words, the angle between the incident light and the normal line (नियमित रेखा) that is perpendicular to the mirror’s surface is equal to the angle between the reflected light and the normal line.

Image Formation in Plane Mirrors

When light is incident on a plane mirror, it reflects off the mirror and forms a virtual image. This image has the same size, but opposite orientation, as the object. For example, if an object is placed in front of a plane mirror, the image formed has the same width and length, but is inverted (upside down). The following diagram illustrates an object and its corresponding image:

When light is incident on the plane mirror, the reflected rays undergo reflection at the reflecting surface according to the law of reflection. This law states that the angle of incidence is equal to the angle of reflection, which also means that the angle between the incident ray and the normal line is equal to the angle between the reflected ray and the normal line. A virtual image is formed at the same side of the reflecting surface as the object, and can be seen if the object is placed at the right distance from the mirror.

The size of the image depends on the distance between the object and the plane mirror. For instance, when the object is placed very close to the mirror, the image is enlarged, but when the object is far away, the image is diminished. The following table shows how the size of the image changes according to the distance of the object from the mirror:

Conclusion

Plane mirrors are flat, highly reflective surfaces that form virtual images of the objects when light rays are incident upon them. The law of reflection states that the angle of incidence equals the angle of reflection, which also means that the angle between the incident ray and the normal line is equal to the angle between the reflected ray and the normal line. The size of the virtual image formed by a plane mirror depends on the distance between the object and the mirror, and can be enlarged or diminished.