The shorter wavelength blue light will produce closer fringes. A diffraction grating bends red light more than blue-the opposite of the color sequence with a prism. You'll photograph what you see through the lens-a spectrum of colors on either side of the streetlights. We'll see in the following chapter that the colors diffracted correlate with the illuminating gas in the streetlights. Fringes become closer together as the slits are moved farther apart.
Circles overlap in relatively smaller segments than the broader overlap of parallel straight lines.
Light emerging from the single opening spreads by diffraction to fall on the double openings, which in effect insures that light that passes through the double openings is part of the same wave front This way, the beams of light that pass through the double openings are the same in intensity and phase-that is, they are coherent. If the distances from slits 1 and 2 differ by one wavelength, light from these two slits will interfere constructively. Then the distances from slits 2 and 3 will also differ by one wavelength, as will the distances from slits 3 and 4, and so on. The distances from slits 1 and 3 will differ by two wavelengths, from slits 1 and 4 by three wavelengths, and so on. The light from every slit will interfere constructively with the light from every other slit provided the distance to the screen is much greater than the size of the grating.