Light - Reflection and Refraction

Mirrors

Mirrors are the objects that are useful in seeing the image of other objects or living beings. These are the optical objects which we use to harness the power of light. When we place an object in front of the mirror, the light waves (or the photons) reflecting back from the surface of the mirror, shows the image of that object. The human beings started manufacturing mirrors around 600BC by bronze, copper, gold, silver, lead etc.

In modern times, the mirrors are manufactured by spraying a thin layer of silver or aluminium at the back of the glass sheet. There are natural mirrors like water through which we can see our image, also there are mirrors artificially made by human beings by various materials like metals, glass etc. There could be of mirrors such as acoustic mirrors (reflecting sound waves) and atomic mirrors (reflecting matter waves).

Mirrors

How does the mirror work?

A light ray is invisible until it reflects from a surface and hits our eyes, which makes it visible. The working of the mirror is based on the law of reflection which says that the angle of reflected ray is same as the angle of incident ray (both angles with reference to the normal ray, also all rays in the same plane).

The light which falls on the surface of the mirror is called as ‘incident light’, and this incident light is when reflected by the mirror surface is called as ‘reflected light’. This reflected light when falls on our eyes enable us to see the image of a particular object. The amount of incident light and reflected light may be the same or different based upon the absorption of light by the mirror.

Also, the reflectivity varies with the wavelength. The refracted light is the light ray which changes its velocity and direction by the effect of the medium in which it travels.

When the smooth surface of the mirror reflects it without disturbing the incoming image, it is a specular reflection. Hence the image produced by a flat mirror is a virtual image. These virtual images cannot be focused, but the concave mirrors can produce a real image which can be projected on a surface. The diffused reflection occurs when the light is scattered upon falling on the surface.

Types of Mirrors

Plane mirrors: They are the flat mirrors which reflects light normally and reverse from left to right.

The curved mirrors are classified in Convex and Concave mirrors:

Convex mirrors: These mirrors bulge outwards. They reflect light rays at a wider angle near the edges as compared to their centre. It creates the image which is slightly smaller than the actual image.

Concave mirrors: We also commonly know them as converging mirrors. They curve inwards and this curvature bounces the light to a specific area i.e. focal point.

Some other types of mirrors are:

Non-reversing mirrors: We also know these as a flip mirror or a true mirror. It allows us to see an object just like we are looking at it directly, instead of the mirror image.

Acoustic mirrors: These acoustic mirrors are big concrete dish-shaped structures which are used to reflect sound instead of light. They can be called as early radar systems.

Two Way mirrors: These mirrors are made by coating a thin layer of reflecting material at one side of the glass. This way some of the light reflects in the lighted side and some light goes on the dark side. These types of mirrors are seen in police interrogation rooms.

Applications

  1. For personal grooming: Mirror is an important part of personal grooming material since ancient times. It can be a small pocket mirror or a full body mirror.
  2. For safety: Mainly convex mirrors are in use for this purpose in large trucks, road junctions, parking lots, and sometimes as a part of security systems.
  3. Rearview mirrors: These are in use in cars or motorbikes, which enables the driver to see the rearview. These mirrors are also in use as rearview sunglasses.
  4. Dental mirrors: These are the mouth mirrors which helps dentists to get a clear view of tight spaces are corners in the mouth.
  5. Signalling: Here the sunlight is used as a light source and signalling can be done for long distances up to 60 km. This technique is in use by the military to transmit information and also for search and rescuing.
  6. Projectors and televisions: Various microscopic mirrors are useful in high definition televisions and video projectors.
  7. Solar Power: Mirror is useful in solar power plants to generate solar energy. They are also useful in solar cookers, solar water heaters etc for domestic uses.
  8. Instruments: The mirror is also useful in instruments like telescopes, dielectric motors and are also useful for the astronomical purpose.
  9. Face to face mirrors: This creates an infinity mirror effect like in Laser, Kaleidoscope etc.
  10. Architecture: The mirrors play an important role in architecture as in the high rise buildings etc. They also serve as design objects and are also a part of art installations. For eg., a large mirror can make a small room look much larger.
  11. Paintings, Sculpture, Decoration, Literature, Entertainment etc. The use of various forms of mirrors in all these places helps in decorating or artwork.

 FAQs

  1. Which mirrors are useful in amusement parks, flat or curved? Explain.

Answer: The amusement parks use curved mirrors or distorting mirrors. We also know them as a funhouse mirror or carnival mirror. The concave or convex sections of these distorting mirror create a funny effect and hence a funny image. The person standing inside a house of a mirror will see all the funny distorted images of his own self which are produced by the use of curved mirrors.  The house of a mirror has its origin from the Palace of Versailles.

  1. How mirrors contribute to harnessing the power of sunlight?

Answer: Solar energy is a renewable source of energy and can be useful in order to preserve the non-renewable source of energy. The mirrors used in solar cookers are concave mirrors which reflect sunlight to a focal point to produce the heating effect. This helps in conserving the other non-renewable energy sources used for cooking. The solar water heaters can help us save electric power, the solar panels in houses or industries can help in saving the other non-renewable energy sources like coal, gasoline etc.

  1. Can mirrors be useful in safeguarding the country? If yes, then how?

Answer: Yes, the mirrors are useful in safeguarding the country. The concave mirrors can be in use in the space mirror and are a dreadful weapon. It can generate a significantly high temperature and can burn an object by merely focusing the sun rays on it. Also, the military uses mirrors for the signalling at long distances in rescue operations. The pilots in the military learn to signal for help by using the mirror, without exposing them to the enemies.

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