Sensitive (Manometric) Flames

This demonstration involves an open propane flame. Ensure adequate clearance from flammable materials (minimum 1 meter). Have a fire extinguisher readily available. Perform in a well-ventilated area to prevent propane accumulation. Never leave the flame unattended.

Check all tubing connections for leaks using soapy water before ignition. Propane is heavier than air and accumulates in low areas. Ensure the propane cylinder is secured upright and the valve can be quickly closed in an emergency. Use only fuel-rated tubing designed for propane service.

Purpose

Sensitive flame burners produce flames that flicker visibly when exposed to high-frequency sound, providing direct visual evidence that sound carries energy. Historically, these flames served as detectors in "optical" experiments using ultrasonic waves.

Two sensitive flame burner assemblies: left unit has a small wheel-like fixture on a rod with round black base, right unit has a brass tube mounted in a gray rectangular block

Figure 1: Sensitive flame burner assemblies. These connect to a propane cylinder via rubber hose and produce flames that respond visibly to high-frequency sound.

Propane Cylinder with Nozzle

1

Warning: Open Flame Hazard

Warning: Fuel System Safety

Purpose

Safety Warnings

Warning: Open Flame Hazard

Warning: Fuel System Safety

Purpose