1. Introduction

In today’s article, we are going to study about ‘ spherical mirror ‘ How beneficial it is and what is theory of concave mirror and convex mirror (spherical mirror). And hence We will also read about some more topics like  reflection of light by spherical mirror, concave mirror, convex mirror,pole, aperture, center of curvature, radius of curvature, focus, focal length, principal axis, sign convention,Relationship between curvature radius (R) and focal length (F) etc given in Detail.  So, take your notebooks in you hand and get ready to study physics in an easy and sorted way.

Reflection of light by spherical mirror

Spherical mirror

If the surface of mirror is Curved then they will be known by the name spherical mirror and they have two types-

  1. Concave mirror
  2. Convex mirror

1) concave mirror

If surface of spherical mirror is polished by one side as shown in fig. A spherical mirror is said to be concave if reflecting surface and center of curvature (center of sphere) is found in the same side then this type of mirror is known as concave mirror and it converge the rays.

2) convex mirror

If reflecting surface and the centre of curvature are found in opposite side then that type of mirror is known as convex mirror. It diverse the rays.

Some important definations

  1. Aperture– the reflecting surface of a spherical mirror is known as aperture of mirror. That is shown in figure by PP’.
  2. Pole– The mid point of reflecting surface is known as pole which which is shown by point “O” in figure.
  3. Center of curvature– It is center point of the sphere of which the mirror is a part. Center of curvature is shown by point C.
  4. Radius of curvature– It is the distance between the pole and center of curvature. Which is given by CO in figure.
  5. Principal axis- It is a line that passing from the centre of curvature and pole is known as principal axis.
  6. Focus– It is a Imaginary point on the principal axis. When incident rays are coming on spherical mirror and parallel to principal axis, then they will go from a fix point F after reflection is known as focus. It is found between principal axis and pole.
  7. Focal length (focus distance)- It is the distance between focus point and pole is known as focal length.
  8. Focal plane- A plane passing from focus and principal axis and this plane will perpendicular to principal axis is known as focal plane.

Sign convention

  1. All distance are measured from pole.
  2. The distance above the principal axis are taken positive and below are taken as negative.
  3. Distance measured in the direction by incident ray are taken positive, which direction opposite of the incident are taken as negative.
  4. The focus distance is positive for convex mirror and negative for concave mirror.

Relationship between curvature radius (R) and focal length (F)-

Consider the concave mirror with C as the centre of curvature, P is pole, F is the focus. The incident ray AB is parallel to the principal axis strike on the mirror at point B. BC is perpendicular on point B.

∠ABC = ∠i angle of incidence

∠CBF = ∠r angle of reflection

Since ABC = ∠BCF i.e. ∠i= ∠i (alternating angle) In ΔBCF =  ∠i= ∠r (by law of reflection) CF= CB.

Since, aperture is small

So BF= FD ∴ CF= FP

∴ F is the centre point of PC so PC= 2PF

R= 2f and

F= R/2


So our article is finished and after completely reading this article, one can easily tell what is spherical mirror. And we have also discussed some more topics spherical mirror, concave mirror, convex mirror,pole, aperture, center of curvature, radius of curvature, focus, focal length, principal axis, sign convention,Relationship between curvature radius (R) and focal length (F) etc

‌So one can say that they got a detailed information about reflection, and basic information about other topics.

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