Mirrors and Their Types

Ever wondered what is the scientific reason behind the mirrors that are used in fairs to attract people (especially kids) as they see themselves in different shapes and sizes? The answer is different types of mirrors that they use.

Mirrors itself has a fascinating history. They were used mainly for personal grooming or for admiring oneself. In olden times, dark and still water pools were used as mirrors. But as time passed, people started to realise that they needed mirrors that has a flat surface and with an acceptable amount of reflectivity.

Manufacturing of mirror

The earliest manufactured mirrors were naturally occurring polished stones from volcanic glass. With this experiment, it was found that glass is the desirable material for mirrors. To increase the reflectivity of glass, metals were coated on one of the sides of the glass. In modern days, silver or aluminium are coated as reflective coatings. Once this was known, different types of mirrors were manufactured.  

Types of glass mirrors

There are different types of glass mirrors based on manufacturing process and reflection type. They are as follows:

  • Aluminium glass mirror: Mirror that is manufactured using aluminium powder and few layers of waterproof protective paints.
  • Low aluminium glass mirror: Mirror that is manufactured using silver and few layers of protective paints. They are widely used as the representation of artwork.
  • Safety glass mirror:  A regular silver coated mirror with a special protective layer is manufactured in order to reduce injuries in case of breakage. They are used in doors, glass walls and furniture.
  • Silkscreen printed glass mirror: Mirrors produced using inorganic colour inks. They are used for decorative purposes.
  • Silver glass mirror: A regular mirror with a silver coating used to produce images by reflection.

Types of mirrors based on the shape

There are two major types of mirrors based on shape and they are a flat mirror and a curved mirror. The curved mirror can be further divided as a concave mirror and a convex mirror.

  • Flat mirror: Also known as the plane mirror has a flat reflective surface. For a plane mirror angle of reflection is equal to the angle of incidence. The image formed on the plane mirror is virtual, same shape and size as that of the object, upright and laterally inverted.
  • Concave mirror: Also known as converging mirror have reflecting surface inwards. They reflect light inward to one focal point. They produce different images depending upon the distance between the object and the mirror. They find applications in reflecting telescopes, in dental mirrors and in aircraft carriers.

Following is the table explaining the effect on the image based on relative position and mirror focal point for a convex mirror:

S (object’s position) F(focal point) Image
S<F Virtual

Upright

Magnified image

S=F No image is formed as the reflected rays are parallel and do not meet
S=2F Real image

Same size

Inverted

Image is formed at the center of curvature

S>2F Real image

Inverted

Diminished image

 

  • Convex mirror: Also known as a diverging mirror or fish eye mirror have reflecting surface outwards. They have an imaginary focal point (F) and centre of curvature (2F) resulting in a virtual image. They are used in vehicles as they produce an upright, diminished image with a wider view of the field.  

Following is the table explaining the effect on an image based on relative position and mirror focal point for a convex mirror:

 

S (object’s position) F(focal point) Image
S>F, S=F, S<F Virtual

Upright

Diminished image

 

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