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Question
Draw a neat two ray diagram for the formation of images in two plane mirrors, when mirrors are at facing each other.
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Solution
When two mirrors are parallel to each other

Consider two plane mirrors XY and PQ facing each other and ‘A’ as an object situated anywhere between them (See figure).
It is clear that mirror XY forms its image in mirror PQ and vice versa. These images by themsleves will act as image mirror or virtual mirrors.
Let us consider the normal incidence towards the mirror XY for object A. First of all an image X1 is formed as far behind, as the object is in front of it. This image X1 will fall in front of mirror PQ, and hence, forms an image X2. The image X2 falls in front of mirror XY and hence, forms an image X3. Thus, it continues and infinite images can be formed.
Similarly, taking normal incidence for mirror PQ image P1,P2, P3 etc. are formed.
In order to draw ray diagram, from point A, draw a divergent beam, meeting mirror PQ at points 1 and 2. With P1 as a reference point, draw rays 1, 3, and 2, 4 meeting mirror XY. With P3 as reference point draw rays, such that they enter the eye.
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