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Two upright plane mirrors, 0.89 m tall, are placed parallel to each other 2.83 m apart. The top of the mirror on the right is then moved back a little so that its surface tilts away from the other mirror at an angle of 13.8° off the vertical. A narrow laser beam passes perpendicularly through a small hole in the very bottom of the mirror on the left and strikes the tilted mirror, from which it reflects. How many times will it reflect from the upright mirror?

  • Physics -

    The first returning beam is aimed up at 2x13.8 = 27.6 degrees. The next returning beam is aimed up at 55.2 degrees. After doubling the angle again, the beam will not return to the upright mirror.

    The answer is twice

  • Physics -

    that answer was wrong.. :S

  • Physics (correction) -

    Your question is best solved graphically. That way, you can verify that each return beam does not pass over the top of the upright mirror.

    It seems that, with that wide separation of short mirrors, even the first return beam will pass over the top of the upright mirror.

    In that case, the answer is never.

  • Physics -

    that answer also turns out to be incorrect haha

  • Physics -

    ha ha to you. Draw the optical diagram.

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