Alternating current through a thin conductor generates sound via thermal expansion

Evidence

When alternating current is passed through a thin conductor, periodic heating takes place in the conductor following the variations in the current strength. This periodic heating sets up temperature waves which … produce a periodic rise in temperature in a limited portion of the medium near the conductor, and thermal expansion and contraction of this layer of the medium determines the amplitude of the resulting sound waves. — Eric J. Heller, Why You Hear What You Hear- An…, 734

Categorization

• DEFINE: The 1917 Arnold–Crandall theory of thermophones: periodic heating sets up temperature waves; thermal expansion of the adjacent medium determines the sound-wave amplitude.