Two Source Interference Pattern 1

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Here is an interactive animation which can be used as an aid to understanding the patterns which are produced when two circular periodic waves interfere. This is often termed a two source interference pattern.

Basic operation:

• The 'Small', 'Medium', and 'Large' radio buttons control the size of the waves.
• The 'Switch phase' button controls the phase of the sources. Directly to its left is a label that describes the current phase of the sources. The applet starts out with the sources in phase. This means that both sources emit a crest at the same time, and, of course, a trough at the same time. (They have the same frequency.) When the sources are out of phase, as one creates a crest the other creates a trough.
• You can click and drag either source to a new location in the medium. When you click your mouse down, you will 'grab' whatever source is closest to the mouse.
• The 'Initialize' button sets all parameters back to their original values.

Although both sources are repeatedly producing waves which move across the medium, a stable, that is, motionless, pattern is set up. As it turns out, the regions of constructive interference do not move, nor do the regions of destructive interference.

These motionless regions have a shape, or pattern, which can be measured. These measurements can be used to calculate the wavelength of the waves which are producing the pattern. In this way one can find the wavelength of a moving wave.

Originally this page held a Java applet animation. The new animation on this page duplicates the former and will hopefully run on almost all devices. If your browser runs Java and you would like to see the original Java animation, click the following link:

Original Java applet animation

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