H3-12
Demonstrate standing sound waves in air excited by convection currents.
A switch is held closed, activating a nichrome wire coil in a vertical glass tube, leading to a very loud roar at about 130 Hz, the fundamental frequency of a four-foot air tube. This is the classic Rijke tube demonstration with an electrical heater replacing a gas burner and screen as the source of the convection currents.

Consider combing this with H3-13, and invite students to make predictions about the differences in pitch and volume.
FS1