Stationary waves, also known as standing waves, are formed by the superposition (interference) of two waves with the same frequency, wavelength, and amplitude traveling in opposite directions.
Here's a breakdown of the process:
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Opposite Directions: The two waves must be traveling in opposite directions. This is often achieved through reflection – a wave travels to a fixed point and is reflected back upon itself.
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Same Frequency and Wavelength: For stable interference and the formation of distinct nodes and antinodes, the two waves need to have identical frequencies and wavelengths. This ensures that the points of constructive and destructive interference remain in fixed positions.
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Similar Amplitude: The amplitudes of the interfering waves should be nearly the same. If one wave is significantly stronger than the other, the interference pattern will be less pronounced, and a true stationary wave will not form. It would result in a wave that appears to move slightly while exhibiting some characteristics of a standing wave.
The interaction of these waves results in:
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Nodes: Points along the medium that appear to be standing still, experiencing minimal or no displacement. These are points of destructive interference where the waves are always out of phase.
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Antinodes: Points along the medium where the displacement is at its maximum. These are points of constructive interference where the waves are always in phase.
Illustrative Example:
Consider a string fixed at both ends, like a guitar string. When the string is plucked, waves travel along the string and are reflected at the fixed ends. The superposition of these traveling waves creates stationary waves, with nodes at the fixed ends and antinodes in between, producing the distinct tones we hear.
In summary, stationary waves are not waves that "stand still" in the literal sense. They are the result of the interference of two identical waves traveling in opposite directions, creating a pattern of fixed nodes and antinodes that gives the illusion of a wave standing in place.
