Estimating RC Time Constants Using Sound

Resistor-capacitor (RC) circuits are a popular topic for both theoretical discussion and experimental investigation in introductory physics. This article presents a novel approach to studying such circuits using a piezoelectric buzzer. A capacitor is discharged through a resistor and the buzzer, and the intensity of the sound produced by the buzzer is recorded as a function of time. Here the recordings are made using a smartphone. The voltage supplied to the buzzer, and thus the intensity of the sound it produces, depends on the voltage across the capacitor. As the capacitor discharges exponentially, the sound intensity decreases linearly since the intensity is measured in units of decibels. The linearly decreasing sound intensity can be analyzed to estimate the discharge time constant of the circuit.