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Question:
A seventh grader asked what would happen if a light were flashed between two mirrors which are parallel to each other.



Replies:
Assuming the light is flashed in all directions (spherically), any light emitted in a direction other than exactly perpendicular to the mirrors will eventually escape. Light emitted straight into the mirrors, will be reflected along the same path, until meeting the opposite mirror, being reflected again, ... essentially without end. However, the light reflecting back in forth will eventually be attenuated by losses in the medium between the mirrors and be losses due to less than 100% reflection at the mirrors. No mirror is perfect; each time the light strikes the mirror, a small percentage will be absorbed rather than reflected. A true pessimist will tell you that due to unavoidable imperfections, the mirrors can not be perfectly parallel on a small enough scale, so all the light gets out.



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