Teaching the Doppler Effect in Astrophysics

TL;DR

This paper presents a simple acoustic demonstration for teaching the Doppler effect in astrophysics, providing visual insight into wave frequency shifts using accessible equipment and a computer fan.

Contribution

It introduces a novel, hands-on acoustic experiment to visually demonstrate the Doppler effect for undergraduate astrophysics education.

Findings

Spectrum widens as fan voltage increases

The technique visually illustrates Doppler shift

Equipment setup is simple and cost-effective

Abstract

The Doppler effect is a shift in the frequency of waves emitted from an object moving relative to the observer. By observing and analysing the Doppler shift in electromagnetic waves from astronomical objects, astronomers gain greater insight into the structure and operation of our universe. In this paper, a simple technique is described for teaching the basics of the Doppler effect to undergraduate astrophysics students using acoustic waves. An advantage of the technique is that it produces a visual representation of the acoustic Doppler shift. The equipment comprises a 40 kHz acoustic transmitter and a microphone. The sound is bounced off a computer fan and the signal collected by a DrDAQ ADC and processed by a spectrum analyser. Widening of the spectrum is observed as the fan power supply potential is increased from 4 to 12 V.