• Written By Rumela_M
  • Last Modified 11-04-2024

General Terms Related to Spherical Mirrors


General terms related to spherical mirrors: A mirror with the shape of a portion cut out of a spherical surface or substance is known as a spherical mirror. Concave and convex mirrors are two kinds of spherical mirrors available. The first mirrors used by humans were probably pools of water, according to the History of Spherical Mirrors in Human Civilization. Polished stone objects were the first known studied and created mirrors. 

Chinese people habitually utilised silver-mercury amalgams to create spherical mirrors around 500 AD. Famous scientist Claudius Ptolemy used curved, polished iron mirrors in several of his studies. This article will discuss the two types of spherical mirrors and essential terminologies related to the spherical mirror.

Types of Spherical Mirror

Spherical mirrors can be of the following two types: 

  • Concave Mirror: In these mirrors, the inner hollow (cave-type) surface reflects the picture while the outer bulged surface is silvered. These mirrors are frequently used as shaving mirrors, in telescopes, and by dentists. Concave mirrors create distorted, enlarged, and virtual images.
  • Convex Mirror: In these mirrors, the image is reflected at the outside (convex) surface while the interior surface is silvered. These mirrors, which are also known as the fish eye or diverging mirrors, are widely used in automobiles. Convex mirrors create distorted, illusory, and erect pictures.

There are various jargons that are unique to each subject. We cannot fully understand an idea or chapter, if we are unaware of the definitions of subject-related terms. One such subject is the spherical mirrors. Below are the terminologies that candidates need to become familiar with in order to fully comprehend the concept of spherical mirrors:

  • Centre of Curvature (C): The imaginary hollow glass sphere is at the centre of the spherical mirror’s centre of curvature, which is typically represented by the letter C. A concave mirror has its centre of curvature in front of it, while a convex mirror has its centre of curvature towards the back.
  • Principal Axis: The straight line that passes through the pole P and the centre of curvature C of a spherical mirror, which is created on both sides, is referred to as the major axis of a spherical mirror.
  • Aperture: The area of a mirror from which light is reflected is called the aperture. The aperture or linear aperture of a mirror is indicated by the diameter of its reflecting surface. A mirror’s size is represented by its aperture.
  • Principal Focus (F): The term ‘principal focus’ describes a point on a concave mirror’s principal axis where all incident rays parallel to the axis and those close by actually meet or converge after being reflected off the mirror. A point on a convex mirror’s major axis known as the principal focus is where all incident rays parallel to the axis and nearby appear to spread out or diverge after being reflected off the mirror. The letter F designates a spherical mirror’s principal focus. A concave mirror consistently rests in front of the concave mirror and has a real focus. The virtual focus of a convex mirror is always located behind the convex mirror.
  • Focal Length (f): The distance between the principal focus (F) and the mirror’s pole (P) is referred to as the focal length of either a concave or a convex mirror. The letter ‘f’ stands for the focal length in both instances, and f equals PF.

Note: The principal focus ‘F’ will perfectly reside at the midpoint of the pole P and the centre of curvature C if a spherical mirror has a small aperture. A convex or concave mirror’s focal length is, therefore, equal to half of its radius of curvature.

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