Concave Mirrors

Edited by Sim, Jen Moreau

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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.
    Concave Mirrors 35467.jpg
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  2. 2
    Pole
    :
    The geometric center of a spherical mirror is called pole or vertex. It is denoted by 'P'.
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  3. 3
    Aperture
    :
    is the distance between the extreme points (MM') of the mirror OR The diameter of the mirror.
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  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.
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  5. 5
    Concave mirrors
    :
    converge to a point, called the principal focus, that is denoted by 'F'.
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  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.
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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.

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  1. 1
    A ray coming parallel to the principal axis is reflected through the principal focus of the concave mirror
    .
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  2. 2
    The ray of light passing the principal focus becomes parallel to the principal axis after being reflected from the mirror
    .
    Concave Mirrors 97965.jpg
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  3. 3
    A ray of light which is coming through the center of curvature is reflected back along the same path
    .
    Concave Mirrors 83179.jpg
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  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"
    .
    Concave Mirrors 56953.jpg
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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.

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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.
    Concave Mirrors 48651.jpg
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  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.
    Concave Mirrors 45961.jpg
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  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.
    Concave Mirrors 27264.jpg
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  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.
    Concave Mirrors 19406.jpg
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  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.
    Concave Mirrors 26755.jpg
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Referencing this Article

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APA (American Psychological Association)
Concave Mirrors. (2017). In ScienceAid. Retrieved Apr 26, 2017, from https://scienceaid.net/Concave_Mirrors

MLA (Modern Language Association) "Concave Mirrors." ScienceAid, scienceaid.net/Concave_Mirrors Accessed 26 Apr 2017.

Chicago / Turabian ScienceAid.net. "Concave Mirrors." Accessed Apr 26, 2017. https://scienceaid.net/Concave_Mirrors.

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