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    Light - Reflection and Refraction
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    State the mirror formula. Is the same formula applicable to both concave and convex mirrors?
    The mirror formula, is a mathematical relation between the object distance u, image distance v and focal length f of a spherical mirror. This relation is
                                 1u+1v =1f 

    In words, we can say that,  

    1Object distance + 1Image distance = 1Focal length 

    This formula is applicable to all concave and convex mirrors.
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    What is lateral inversion of an image ? What is the cause of lateral inversion?
    Lateral inversion: If we stand before a plane mirror and move our right hand, our image appears to move its left hand. Infact, our entire image is reversed sideways. This sideways reversal of the image is known as lateral inversion.
    Lateral inversion: If we stand before a plane mirror and move our rig
    Fig.  Lateral inversion before a mirror
    Cause of lateral inversion: Lateral inversion is due to the fact that in a plane mirror the image is as far behind the mirror as the object is in front of it and that the front of the image and the front of the object face each other. The laterally inverted image of the word LEFT is as shown in Fig. The images of symmetrical letters like A, H, I, M, O, T, U, V, W, X, Y, 8 are not affected by lateral inversion.
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    You are given three mirrors of equal size—concave, convex and plane. How will you identify them without touching their surfaces?

    Identification of mirror: 

    We are given three mirrors. Let's see our faces in each mirror, turn by turn. Initially, keep the face close to the mirror but, slowly move away from the mirror. 

    1. If the image formed on the mirror is of the same size as our face but laterally inverted (i.e., left face looks right and vice-versa) for all positions, then it is a plane mirror. 

    2. If the image formed is erect and enlarged initially but gets inverted as the face is moved away, then it is a concave mirror. 

    3. If the image formed is erect and smaller in size for all positions, then it is a convex mirror. 

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    What happens to the size of the image formed by a convex mirror, when an object is gradually moved towards the mirror?
    Fig (a).As shown in Fig.(a), when the object is at position A1B1, it
    Fig (a).
    As shown in Fig.(a), when the object is at position A1B1, its virtual image is at a1b1. When the object is at position A2B2, its virtual image is at a2b2. So, when an object is gradually moved towards the pole of a convex mirror, its image also moves towards its pole and gradually increases in size till it has a size almost equal to that of the object. However, the image is always formed between F and P.
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    It is desired to obtain an erect image of an object, using a concave mirror of focal length 20 cm.
    (i) What should be the range of distance of the object from the mirror?
    (ii) Will the image be bigger or smaller than the object.
    (iii) Draw a ray diagram to show the image formation in this case.

    (i) The object should be placed between 0 to 20 cm from the pole of the mirror.
    (ii) The image will be bigger than the object.
    (iii)
      (i) The object should be placed between 0 to 20 cm from the pole of t
    Fig. Image formed by a concave mirror with the object between F and P
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