Tutorial details

The tutorial uses water waves to help students related the representations and formalism to real-world behavior.

It begins by having students interpret the a diagram showing circular wavefronts due to a single point source. They are then given a diagram that shows wavefronts due to two point sources that are in phase and 1.5λ apart. Students identify points at which the water surface is (1) farthest above equilibrium, (2) farthest below equilibrium, and (3) at equilibrium. They come to recognize that maximum constructive interference occurs at points where the difference in distances to the sources, ∆D, is a whole number of wavelengths, and that nodal lines occur where ∆D is an odd number of half wavelengths. (Students are told to ignore any differences in amplitude of the waves.) At the end of the tutorial, students examine the effect of the source separation on the number of nodal lines and lines of maximum constructive interference and on their locations.

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Prerequisite tutorials

The Propagation and refraction of periodic waves tutorial is a prerequisite to Two-source interference.

Other prerequisites

It is expected that students have a basic understanding of wavelength, frequency, and phase difference. It is helpful, but not necessary, for students to have completed Propagation and refraction of periodic waves.

Equipment

List

• crayons or colored pens
• handouts

Discussion