Single Slit Diffraction

When monochromatic light (light of a single wavelength, for example from a laser) passes through a single narrow slit, it diffracts and produces a pattern of bright and dark fringes on a screen.The pattern has a wide, bright central maximum, with narrower, dimmer maxima on either side separated by dark minima. The central maximum is twice as wide as each of the other maxima, and it is much more intense. The intensity of the side maxima decreases with distance from the centre.The dark fringes are where light from different parts of the slit arrives in antiphase and cancels.Effect of slit width: making the slit narrower makes the light spread out more, so the central maximum becomes wider (and dimmer, as less light gets through).Effect of wavelength: light with a longer wavelength diffracts more, so red light gives a wider pattern than blue light through the same slit.White light: each colour produces its own pattern with a different width. The centre of every pattern is at the same place, so the central maximum is white. Further out, the colours separate, so the side maxima are coloured, with blue on the inside edge and red on the outside edge of each.Worked example: a laser pattern through a slit has a central maximum 12 mm wide. The first side maxima are therefore about 6 mm wide. If the slit is replaced by a narrower one, the central maximum becomes wider than 12 mm.