Plane Mirror


•    Reflection is defined as the phenomenon of change of path of light and bouncing back into the same medium on striking to a shiny and smooth surface. An object can be seen when light reflects from it and enters our eyes.
•    The surface on which light strikes is called the reflecting surface. On the basis of the type of reflecting surface, reflection of light is classified as
Regular reflection: In regular reflection, a beam of parallel rays incident on a smooth, polished and regular surface remains parallel after reflection. Regular reflection results in the formation of clear images.  
Irregular (diffused) reflection: In irregular (diffused) reflection, a beam of parallel rays incident on an irregular surface becomes non-parallel after reflection. Irregular reflection results in the formation of hazy image or no image at all.
•    Reflection of light is governed by two laws.

                                                         

First law states that the angle of incidence (i) is always equal to the angle of reflection (r).
Second law states that the incident ray, reflected ray and the normal at the point of incidence, all three lie at the same plane.
•    When the light coming from an object reflects from a plane mirror, its image is formed in the plane mirror. The image formed is virtual, erect, of the same size as object, at the same distance as object behind the mirror and laterally inverted.

                                                       

•    Lateral inversion is the phenomenon in which left side of the object appears right and right side of the object appears left in the image formed in the plane mirror. Virtual images cannot be obtained on the screen whereas real images are the one which can be obtained on the screen.
•    Using the two plane mirrors set at different angles to each other, different number of images can be obtained. The number of images formed can be calculated using the formula,

                                                                   

•    Periscope, Kaleidoscope, solar cookers, etc., make use of plane mirrors.


 

 

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  • Q1

    What is diffused reflection? Does it obey the laws of reflection?

    Marks:2
    Answer:

    When parallel rays of light fall on an irregular surface, the reflected rays appear in different directions obeying the laws of reflection. These reflected rays falls in different directions because the normal at different points of incidence is in different directions due to the irregularities in the surface.

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  • Q2

    Name the mirror which always produces an erect and virtual image.

    Marks:1
    Answer:

    Plane mirror always produces an erect and virtual image.

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  • Q3

    Define Image.

    Marks:1
    Answer:

    When the rays of light, diverging from a point and after reflection or refraction, actually meet or appear to meet at some other point, then that point is called the image of the object.

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  • Q4

    Where will the image formed, if we look into a plane mirror?

    (i) on the surface of the mirror. (ii) in front of the mirror.

    (iii) behind the mirror.

    Marks:1
    Answer:

    (iii) If we look into a plane mirror, the image will be formed behind the mirror.

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  • Q5

    What do you understand by the term reflection of light?

    Marks:1
    Answer:

    It is the phenomenon due to which a beam of light travelling through a certain medium, on striking some surface, bounces off from it, in some other direction.

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