Reflection from Plane Mirrors

Plane Mirrors

Plane mirrors are commonly used as looking glasses. We use them while dressing, Combing, and so on. A plane mirror is made from a glass plate, a few millimetres thick. One surface of the glass is polished to a high degree of smoothness, forming the front surface of the mirror. The back surface is silvered, i.e., coated with a thin layer of silver, aluminium or some other shiny, opaque material. A coat of opaque paint behind this layer protects the silvering. When light from an object falls on the front surface, most of it enters the glass plate and falls on the silvered surface.

Reflection From Plane Mirrors:

An image by a plane mirror is formed when light from the object reaches our eyes after reflection from the plane mirror. As the light enters our eyes we can see all the details of the object. Plane mirror is the surface with flat reflecting surface.

Uses of Plane Mirror:

The various uses of plane mirror:

Plane mirror are used as looking mirrors in our homes.

The mirrors are fixed on the walls to give false dimensions in the showrooms.

The mirrors are used in kaleidoscope, periscope and solar cookers.

Formation of Image:

When an object is placed in front of a plane mirror, its image is formed in the plane mirror. We can find the location of the image of an object in a plane mirror by using the laws of reflection of light.

In the figure below the object is placed in front of a plane mirror. An image of the object will be formed in the plane mirror. We can locate the position of image of this object in the plane mirror by drawing a ray diagram.

We take two diverging rays from the object. In the figure above the two rays have been marked as red and blue.

The red and the blue rays strikes the mirror and are reflected back. In the figure we have drawn two perpendiculars at the point of incidence which act as normal at that point.

For each ray angle of incidence is equal to the point of reflection, hence it follows the laws of reflection.

The two reflected rays are diverging rays so they can not meet in front of the mirror to form a real image. So we produce the reflected rays backwards i.e. behind the mirror by dotted lines. On producing backwards the reflected rays meet at point behind the mirror.

The reflected rays enter our eyes seems to be coming from point behind the mirror. So that point is the image of the object.

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Sample Questions

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Question : 1

Which of the following are correct ? (a) A plane mirror is made from a glass plate, a few millimetres thick. (b) The plane mirrors are used in kaleidoscope, periscope and solar cookers. (c) When an object is placed in front of a plane mirror, its image is formed in the plane mirror.
A. Only (a) and (b) is correct .	B. Only (b) and (c) is correct .	C. Only (a) and (c) is correct .	D. All of these .
Right Option : D
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Question : 2

Which of the following are correct : (a) Plane mirror are used as looking mirrors in our homes. (b) A plane mirror is made from a glass plate, a few millimetres thick. (c) One surface of the glass is polished to a high degree of smoothness, forming the front surface of the mirror. (d) The back surface of mirror is silvered, i.e., coated with a thin layer of silver, aluminium or some other shiny, opaque material.
A. Only (a) and (b) are correct.	B. Only (a) and (c) are correct.	C. Only (a) and (d) are correct.	D. All of these.
Right Option : D
View Explanation