Physics
Physics
Problem
A double-slit apparatus has slit separation and slit width . It is illuminated by light of wavelength . (a) How many interference bright fringes (including the central maximum) are visible within the central diffraction envelope? (b) State the highest order bright fringe that appears inside this envelope.Intuitive explanation
The key is recognizing that you're dealing with both single-slit diffraction (which narrows the overall brightness pattern) and double-slit interference (which creates the fine fringes). The single-slit envelope acts like a dimmer switch on the interference pattern—some of those bright fringes will fall in the dark regions of the diffraction pattern and vanish. Calculate the diffraction minima positions first, then see which interference maxima get wiped out.
Intuitive explanation
The key is recognizing that you're dealing with both single-slit diffraction (which narrows the overall brightness pattern) and double-slit interference (which creates the fine fringes). The single-slit envelope acts like a dimmer switch on the interference pattern—some of those bright fringes will fall in the dark regions of the diffraction pattern and vanish. Calculate the diffraction minima positions first, then see which interference maxima get wiped out.