Explain how a periscope can help to see a tree behind a wall, which cannot be seen directly.
The figure shows a tree behind a high wall which we canno see direclt. We can, however, see this treee by using a periscope as follows:The upper hole of periscope is turned towards the object to be seen (here a tree) so that mirror M1 faces the object. And we look into the periscope from the bottom hole in front of lower mirror M2. The light rays coming from the tree fall on the plane mirror M1. Mirror M1 reflects these rays of light towards the mirror M2. The mirror M2 then reflects the light towards the eye of the person looking into periscope through the lower hole. Since the light rays coming from the tree enter the eye, it is possible to see the image of the tree in the lower mirror M2 (even though the tree cannot be seen directly).
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