The third-order bright fringe of 610-nm light is observed at an angle of $31 ^\circ$ when the light falls on two narrow slits. How far apart are the slits?
Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014. Reprinted by permission of Pearson Education Inc., New York.
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$3.6 \; \mu m$