# Concave Mirrors

Edited by Sim, Jen Moreau

## Concave Mirror

Is defined as a spherical mirror with a polished inner side.

## Definitions of Special terms

1. 1
Center of Curvature
:
is the center of the hollow spherical mirror. Its radius is called the radius of curvature.It should be noted that the center of curvature (denoted by 'C') of a concave mirror is in front of the mirror whereas that of a convex mirror is behind the mirror.
2. 2
Pole
:
The geometric center of a spherical mirror is called pole or vertex. It is denoted by 'P'.
3. 3
Aperture
:
is the distance between the extreme points (MM') of the mirror OR The diameter of the mirror.
4. 4
Principal Axis
:
The straight line passing through the pole 'P' and the center of curvature 'C' is called the principal axis. AB is the principal axis in the fig.
5. 5
Concave mirrors
:
converge to a point, called the principal focus, that is denoted by 'F'.
6. 6
Focal Length
:
The distance between pole 'P' and the principal focus 'F' is called focal length. It is denoted by 'f'. It is equal to half the radius of curvature. f = r/2 The focal length of a concave mirror is considered as positive.

## Rules for Obtaining Images Formed by a Concave Mirror

When an object is placed in front of a concave mirror, an image is formed. The point of intersection of any of the two rays shows the image point "I" of object "O". The rays which are reflected from a concave mirror follow certain rules as under.

1. 1
A ray coming parallel to the principal axis is reflected through the principal focus of the concave mirror
.
2. 2
The ray of light passing the principal focus becomes parallel to the principal axis after being reflected from the mirror
.
3. 3
A ray of light which is coming through the center of curvature is reflected back along the same path
.
4. 4
A ray of light incident on the pole, at an angle "O" with the principal axis, is reflected by the same angle "O"
.

## IMAGE FORMATION BY CONCAVE MIRROR

The type of images formed by a concave mirror depends on the position of the object to the mirror. If the distance of an object say OO' from a concave mirror is changed, then the nature, size, and location of the image are also changed.

Formation of different images depending on the position of the object are shown below:.

1. 1
First Position
:
(Beyond 'C'). When the object is placed beyond the center of curvature C, then the image will be formed between the focus and the center of curvature; between 'F' and 'C'. This image will be real, inverted and smaller in size.
2. 2
Second Position
:
(at 'C'). When the object is placed at the center of curvature. The image is formed at the center of curvature C and is real, inverted and equal in size.
3. 3
Third Position
:
(Between 'C' and 'F'). When the object is placed between the center of curvature C and focus F, then the image formed will be beyond C. This image will be real, inverted and larger than the object.
4. 4
Fourth Position
:
(at 'F'). When the object is placed at the principal focus, then the image will be real, inverted, larger and at infinity.
5. 5
Fifth Position
:
(between 'F' and 'P'). When the object is placed between the pole and principal focus, then virtual, erect and larger image will be formed.

APA (American Psychological Association)
Concave Mirrors. (2017). In ScienceAid. Retrieved Apr 22, 2018, from https://scienceaid.net/Concave_Mirrors

MLA (Modern Language Association) "Concave Mirrors." ScienceAid, scienceaid.net/Concave_Mirrors Accessed 22 Apr 2018.

Chicago / Turabian ScienceAid.net. "Concave Mirrors." Accessed Apr 22, 2018. https://scienceaid.net/Concave_Mirrors.

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## Article Info

Categories : Physics

Recent edits by: Sim

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