When talking about phase difference (φ) we can be referring to two separate waves, or two particles in the same wave, and it tells us how far or behind one wave/ particle is from another. Path difference also refers to different waves, but it refers to the difference in the distance that the two waves have travelled. If two waves overlap then this is known as interference, interference can either be constructive or destructive, depending on the phase difference of the waves. The path difference can be used to determine the phase difference of two waves using the following calculation.
The double slit experiment, as shown in the diagram, can be used to create an interference pattern on a screen or it can be detected using a suitable wave detector. Light from a single source travels through each slit, and they then act as two coherent sources of light. Light diffracts through each slit and the interference of the two sources can be recorded in order to observe areas of constructive and destructive interference. The double slit experiment is often done with a light source so that the ‘fringes’ or strips of light created by the two sources can be observed on a screen; the intensity of the light in each fringe can be used to create a graph.
During the double slit experiment, light waves diffract and interfere with one another to form an interference pattern on an observation screen. This interference pattern is bands of alternating dark and light strips known as fringes. Different light sources create different fringe spacings and the fringe spacing of a particular experiment can be used to calculate the wavelength of the light, and it is shown in the diagram.
When light travels through a double slit experiment the interference experienced by the light waves creates an interference pattern. There are areas of constructive and destructive interference that are plotted onto a graph to create the pattern shown in the diagram.