A student analyzes the fourth bright fringe produced by a He–Ne laser (wavelength 633 nm) passing through a double slit with a separation of 12 µm. The screen is 1.5 m away.
(a) Using the small-angle method, the student finds a fringe position of 31.7 cm from the centre.
(b) A more exact calculation that does not assume small angles gives a fringe position of 32.4 cm.
What is the percentage error introduced by using the small-angle method in this case?
(a) 5.6 %
(b) 2.3 %
(c) 9.1 %
(d) 0.7 %