Diffraction Minima Condition Single Slit — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Diffraction Minima Condition (Single Slit) Fraunhofer diffraction by a single slit where the light source and screen are effectively at infinity. The slit is divided into 2n equal zones. Path difference between rays from the top and bottom of the slit is a sin(theta). For a minimum, the slit is divided into even number of parts such that pairs of secondary wavelets cancel each other (phase difference of pi). If path difference is n lambda, then for every point in one half, there is a point in the other half with path difference lambda/2, leading to destructive interference. n must be a non-zero integer. The slit width 'a' must be of the order of the wavelength 'lambda' for observable diffraction. Light must be monochromatic and coherent. Confusing this with the maxima condition in Young's Double Slit Experiment (YDSE). In YDSE, d sin(theta)=n lambda is the condition for maxima. Thinking n=0 produces a minimum; n=0 actually corresponds to the central maximum. Assuming the angle theta is always small; if 'a' is very small, sin(theta) can be large and the small-angle approximation (sin(theta) approx theta) cannot be used.