Difference Between Concave and Convex Mirrors

The difference between concave and convex mirrors is among the most commonly asked questions in school level physics examinations. Here’s what you need to know.

We all know what mirrors are. They are reflective surfaces, often made from glass coated with a reflective material. Mirrors can also be made from polished reflective metal, such as stainless steel. Most of us use mirrors every day – in our bathrooms and when we get dressed.

What is a Concave Mirror?

A concave mirror is a mirror that is curved inwards towards the middle. A simple example of a concave mirror that we all use is a shiny spoon. The inwardly curved surface of a spoon forms a concave mirror.

Concave mirrors are also known as converging mirrors as reflected light rays converge on a focal point in front of the mirror surface. The image formed in a concave mirror is real, inverted and enlarged unless the reflected object is closer to the mirror surface than the focal point.

If an object is closer to a concave mirror than the focal point the reflected image is no longer inverted, virtual and enlarged.
The magnifying properties of concave mirrors are a key reason why they are used as shaving mirrors. They are also used in reflecting telescopes, car headlamps, searchlights and flashlights.

What is a Convex Mirror?

A convex mirror is the opposite of a concave mirror with a curved surface that bulges outwards toward the middle. The reverse side of a shiny spoon is effectively a convex mirror.

Convex mirrors are also known as diverging mirrors as light rays reflected from the convex surface diverge and spread outwards. The image formed in a convex mirror is virtual, erect (the right way up) and diminished in size.

Convex mirrors are used as rear view mirrors in automobiles as they provide a wide-angle, expanded field of view. Another motoring related application is the common use of convex mirrors to provide drivers with a view of a road as they exit their driveways. They are also widely used as retail store security mirrors, providing retail staff with an expansive view of their shop to help prevent shoplifting.

Key Differences Between Concave and Convex Mirrors

Here’s a list of the primary differences between concave and convex mirrors.

  • Concave mirrors curve inwards, convex mirrors curve outwards.
  • The focal point for a concave mirror is in front of the mirror while the focal point for a convex mirror is behind the mirror surface.
  • Images formed in concave mirrors are real, inverted and enlarged – unless the reflected object is within the focal length, in which case the images are virtual, not inverted but still enlarged.
  • Images formed in convex mirrors are virtual, non-inverted (erect) and diminished (smaller).
  • Concave mirrors are commonly used in lighting applications such as car headlights, search lights and torches. They are also used as shaving or makeup mirrors and the small mirrors used by dentists are concave.
  • Convex mirrors are used as rear view mirrors in automobiles, security mirrors in shops, road safety mirrors to provide drivers with a wide angle view of what’s on a road.
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