A double-slit experiment uses slits separated by 0.20 mm and 650 nm light. The screen is 1.8 m from the slits.
(1) Calculate the exact lateral position y_exact of the second-order bright fringe on the screen.
(2) Using the small-angle approximation, calculate y_approx for the same fringe.
(3) Compute the percent error between y_exact and y_approx and state whether the approximation is valid if the acceptable error threshold is 0.5 %.