Physics
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Convex Mirror- Principal Focus, Image Formation, Uses

A convex mirror has a reflective surface that is curved outward and away from the light source. Convex mirrors reflect light outward away from principal focal point.

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Posted by Mahak Jain, 28/7/2021
Convex Mirror- Principal Focus, Image Formation, Uses

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Spherical mirrors and lenses have made a very important and integral part of life. Many of us might be visionless without these mirrors and lenses. Concave and convex mirrors are most commonly used spherical mirrors .Learn about convex mirror in this article.

Click here to learn about concave mirrors.

Define Convex Mirror

If the cut part of the hollow sphere is painted from inside, then its outer surface becomes the reflecting surface. This kind of mirror is convex mirror.

Sign Convention for Concave Mirrors

Directions taken are as follows and shown in figure below:

  • Distances behind silvered face of mirror are positive.
  • Distances in front of reflecting face are negative.
  • Height above principal axis is positive.
  • Height below principal axis is negative.
sign convention for convex mirror

Define The Principal Focus of a Convex Mirror

The light rays coming parallel to the principal axis appears to converge on the principal axis after reflecting from a convex mirror. The point, where they appear to meet is called principal focus of a convex mirror. Point F is principal focus in the image below.

Note that, focal length for convex mirrors are positive.

Principal Focus of a Convex Mirror

Radius of Curvature and Focal Length of Convex Mirror

Radius of the sphere of which mirror is a part is the radius of curvature. In simple convex mirrors (covered in this blog) focal length is half of radius of curvature.

Thus, f = c/2

Image formation by Convex Mirror

Object PositionImage PositionImage Characteristics
At infinityAt Focus
Behind the Mirror
Highly Diminished
Virtual
Erect
Between Infinity
And the Pole
Between P and F
Behind the Mirror
Diminished
Virtual
Erect

Ray Diagrams

Image formation by Convex Mirror

Characteristics of Convex Mirrors

  • A convex mirrors diverge light when they strike on its reflecting surface. Hence the name diverging mirror.
  • Convex mirrors always form virtual, erect, and diminished images, irrespective of the distance between the object and the mirror.

Uses of Convex Mirrors

  • Convex mirrors are widely used as rear view mirrors of vehicles. This is because it can diverge light beams. Therefore, covers wider area.
  • Convex mirrors are widely used for making magnifying glasses. Thus, in order to make a magnifying glass, we place two convex mirrors back to back.
  • You might have seen mirrors on turns and squares on roads. Foremost, their aim is to visualize wider area to avoid accidents. Thus, for that purpose convex mirrors are used.

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