Standing waves on a string and electromagnetic induction

Standing waves on a string are a popular classroom demonstration which helps students understand such fundamental acoustic concepts as wavelengths, interference, and resonances. The close connection between this demonstration and stringed musical instruments helps bridge the gap between the science classroom and other interests they may have. In this version of the demonstration, we replace the string with a copper wire and add a permanent magnet. This allows the vibrations in the string to be directly translated into an electrical signal which can be broadcast through a standard stereo amplifier and speakers similar to an electric guitar pickup. The effects of string tension and length can then be explored. Alternatively, an ac can be driven through the wire creating a periodic driving force from the magnetic field of a precise frequency allowing standing waves to be established on the string. More advanced students can also examine the Fourier transform of the signal produced when the wire is struck and find peaks at the resonant frequencies.