Question

At what angles should mirrors be placed in a Periscope so that the incident ray and reflected rays are parallel to each other?

Answer 1

At 45° angles should mirrors be placed in a Periscope so that the incident ray and reflected rays are parallel to each other. These mirrors are placed at the angle of 45° because=====See the image.

When we see anything from periscope then the mirrors reflect and give the clear image.

Answer 2

45°
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the angles at which the mirrors should be placed  in a Periscope so that the incident ray and reflected rays are parallel to each other is 45°
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when the mirrors are placed in 45° they will be opposite to each other and a better image is possible as they will be parallel and opposite