^Intensity of fringes
Intensity of fringes at point P is
Here I0 is the intensity of central maxima. For nth secondary maxima,
From above points we have the following plot.
Also using the relation of intensity we can say
- Maximum intensity is central maxima.
- Most of the light is diffracted between the two first order minima.
- The intensities of secondary maxima relating to the intensity of central maximum are in ratio,
- The intensity of the first secondary maximum is just 36 % of that of the central maximum.
- As the width of a secondary maximum thus as the slit width is increased, the secondary maxima get narrower. If the slit is sufficiently wide, the secondary maxima disappear and only the central maximum is obtained which is the sharp image of the slit and not a diffraction, thus a distinct diffraction pattern is possible only if the slit is very narrow.