The differences between our analysis of double-slit interference patterns and single-slit diffraction patterns were discussed today.
In double-slit interference we focus on the differences in lengths (measured in wavelengths of light) of the paths taken by light from one slit to a point in the interference pattern from the length of the path taken by light from the other slit to the same po\int in the pattern. In this analysis we can account for every fringe and node. In single-slit diffraction we focus on the first node (dark area) on either side of the central fringe. In this analysis we consider each point in the slit to be a source of waves of light. When light from one half of the slit cancels out light from the other half of the slit when it arrives at the diffraction pattern, the dark area (the node) results. In this analysis we account for only the two nodes on either side of the central fringe and the central fringe itself.
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