Sagnac-Effect

Links: Wikipedia; Sagnac (1913); Johnson (2009)

The experiment of Sagnac showed that light beams from same source which are reflected  by mirrors around a rotating system along identical routes but in opposite direction show interference patterns which depend on velocity of rotation. The shift in interference fringes were conform to the different distances that the opposite light beams travelled due to the rotation. 

Test Question 4:

What can be concluded by this experiment?

A) The run length of the light beam will be shorter, when the light moves against the direction of equally moving detector and source and vice versa.

B) The light speed relative to detector and source will be higher, when the light moves against the direction of equally moving source and detector and vice versa.

C) The Sagnac effect is exclusively valid for motions which are rotations.

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