Mirrors Placed At An Angle


 
 
Concept Explanation
 

Mirrors Placed At An Angle

Multiple Reflection

We know that plane mirror reflects light falling on it. This reflected ray can act as incident ray for another mirror. This process of reflection of light several times between reflecting surfaces is known as Multiple reflection of light.

  • Multiple reflection can be obtained by placing more than one mirror at certain angle to each other which results in reflection of light for multiple times between reflecting surfaces.
  • Mirrors Placed At An Angle:  In case of multiple reflections the ray that is incident on one mirror after getting reflected at more that one mirror bounces back in the same medium. Applying the laws of reflection we can calculate the angle at which it will bounce back.

    Illustration: Two mirrors are inclined at an angle of 1200 . A ray is incident on mirror M1 at an angle of 650 to the normal. Find the direction of the ray after it is reflected from mirror M2.

    Solution: The diagram showing the arrangement of the mirrors is as follows:

    At mirror M1 the incident ray makes an angle of 650 with the normal. So,

    Angle of incidence i = 650

    According to the laws of reflection angle of reflection r = 650

    As the normal makes an angle of 900 with the surface of the mirror

    So the reflected ray makes an angle of = 900 - 650 = 250 with the surface of the mirror M1

    The reflected ray forms a triangle AOB with the two mirror surfaces,

    Now angle BAO = 25^0

    angle AOB = 120^0

    From angle sum property of triangle AOB

    angle AOB + angle BAO + angle ABO = 180^0

    Rightarrow ;;120^0 + 25^0 + angle ABO = 180^0

    Rightarrow ;;145^0 + angle ABO = 180^0

    Rightarrow ;; angle ABO = 180^0 - 145^0= 35^0

    The first reflected ray is incident on mirror M2 and makes an angle of 350 with the surface of the mirror

    The incident ray makes angle of = 900 - 350 = 550 with the normal to the surface of the mirror M2

    Now angle of incidence for mirror M2 = 550

    According to the laws of reflection angle of reflection r = 550

    Hence the second reflected ray makes an angle of 550 with the normal to the surface of the mirror M2

    Number of Images Formed By An Inclined Mirrors:

    The number of images formed by two plane mirrors depends on the angle between them. If two plane mirrors are placed at an angle of X degree, then the number of images formed (n) is given by the formula

    Formula to find number of images formed when two mirrors are placed side by side

    Number ;of ;images = frac{360}{X}-1,;;;;;if; frac{360}{X}; is; even

    Number ;of ;images = frac{360}{X},;;;;;if; frac{360}{X}; is; odd                                                                                                                                                                      

    Illustration: Find the number of images formed when angle between two mirrors is 180^{circ}.

    Solution: By using formula we get  

      frac{360}{180}-1Rightarrow 2-1=1

    which means only one image is formed .

    Illustration: Find the number of images formed when angle between two mirrors is 90^{circ}.

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    Sample Questions
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    Question : 1

    Which of the following are correct ?

    (a) This process of reflection of light several times between more than one reflecting surfaces is known as multiple reflection of light.

    (b) In case of multiple reflections the ray that is incident on one mirror after getting reflected at more that one mirror bounces back in the same medium .

    Right Option : C
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    Explanation
    Question : 2

    This process of reflection of light several times between more than one reflecting surfaces is known as ___________________ .

    Right Option : C
    View Explanation
    Explanation
    Question : 3

    In case of ____________________ the ray that is incident on one mirror after getting reflected at more that one mirror bounces back in the same medium.

    Right Option : A
    View Explanation
    Explanation
     
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