Fringe Width Ydse — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Fringe Width (YDSE) Applicable to Young's Double Slit Experiment using monochromatic light and small angle approximation (D >> d). Path difference for the nth bright fringe is Delta x = d sin(theta) = n lambda. For small angles, sin(theta) is approximately y/D, where y is the distance from the central maximum. Distance of nth fringe: y n = n lambda D/d. Fringe width beta = y n - y n-1 . The light source must be coherent. Small angle approximation (sin theta is approximately tan theta). The medium between slits and screen is uniform (usually air/vacuum). Thinking that fringe width depends on the order of the fringe (n); in YDSE, it is constant for all fringes. Forgetting to change lambda if the entire apparatus is submerged in a medium like water (lambda medium = lambda air/mu).