The other bright red bands to the left and the right of the central maximum are assigned whole number values of 1, 2, 3. The red band of maximum brightness located in the center of screen (the central maximum) is assigned an order number of m = 0. The dark bands correspond to the projection of the nodal lines onto the screen.Īs mentioned earlier in Lesson 3, each antinodal and nodal line is assigned a number or order value (m). The bright bands to the right and the left of the central bright band correspond to the projection of other antinodal lines onto the screen. In the above pattern, the central bright band where light displays maximum intensity corresponds to a point on the central antinodal line. Thus, a pattern of bright red and dark fringes or bands is observed on a screen as shown in the diagram below. Red laser light passing through two narrowly spaced slits is typically used in the classroom to produce this effect. And the nodes are locations where light from the two individual sources are destroying each other and correspond to points of darkness or minimum intensity (sometimes referred to as minima). That is, the antinodes are locations where light from the two individual sources are reinforcing each other and correspond to points of brightness or maximum intensity (sometimes referred to as maxima). Locations where light destructively interferes corresponds to an abnormally dark spot. Locations where light constructively interferes corresponds to an abnormally bright spot. When light from the two sources is projected onto a screen, the pattern becomes quite evident. Thus, the pattern formed by light interference cannot be seen unless it is somehow projected onto some form of a screen or a sheet of paper. Light traveling through the air is typically not seen since there is nothing of substantial size in the air to reflect the light to our eyes. But what would be observed in a two-point source light interference pattern?Īs in any two-point source interference pattern, light waves from two coherent, monochromatic sources (more on coherent and monochromatic later) will interfere constructively and destructively to produce a pattern of antinodes and nodes. And there would be other locations where sound cancellation occurs and the sound intensity was relatively faint or not even heard at all (nodes). For sound waves produced by two speakers, the interference pattern would be characterized by locations where the sound intensity was large due to constructive interference (antinodes). And there would be other locations where the water was relatively undisturbed (nodes). For water waves in a ripple tank, the resulting pattern would include locations along the water's surface where water was vibrating up and down with unusually large amplitudes (antinodes). All waves behave the same, whether they are water waves created by vibrating sources in a ripple tank, sound waves produced by two speakers, or light waves produced by two light sources. The discussion of the interference patterns was introduced by referring to the interference of water waves in a ripple tank. The antinodal positions are present at locations where constructive interference always occurs and the path difference is equivalent to a whole number of wavelengths. The nodal positions are present at locations where destructive interference always occurs and the path difference is a half-number of wavelengths. Previously in Lesson 3 we have seen how circular waves from two sources can interfere in the surrounding space to produce a pattern of antinodes and nodes.

Light intensity wavelength equation