Glowing Rings
Noah Pechter
Award: Top 100
School: evanston township high school
Teacher: daniel dubrow
Category: Contrived
Photo #21102
Glowing Rings
I took this photo in a dark room with my camera set to a 10-second shutter speed. My friend held a multicolored LED string light at both ends and swung it around in a circle. This let the camera capture the full range of the string's motion as it spun.
The resulting photo shows a standing wave, which is a pattern formed when two waves with equal amplitude and frequency travel in opposite directions and interfere. In standing waves, nodes are points with zero displacement through destructive interference. This is seen as the rings shrink towards where the string is being held. Antinodes are points with maximum displacement, which we can see in the middle of the string with the largest loops.
The shape of the wave corresponds to a specific harmonic of a standing wave. For example, in the nth harmonic, there are n antinodes and n+1 nodes, with the distance between two nodes being half of the wavelength. Swinging the string faster or slower creates a different harmonic, resulting in a different number of loops and a longer or shorter wavelength. Only specific frequencies with a whole number of half-wavelengths that fit the string's length will survive, as anything else would cancel itself out.
Standing waves aren't only visible by spinning a string; they appear in the vibrating strings of a guitar or the arc of a jump rope. This image shows how some of the most elegant physics can be seen by simply swinging a string.
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