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Physics · 3.4 Sound · Oscilloscope & speed of sound

Sound. Hear it.

Sound is a longitudinal wave of compressions and rarefactions. Change the frequency (pitch) and amplitude (loudness) and watch the oscilloscope trace. Calculate wave speed from v = fλ, and explore the echo method for the speed of sound.

0625 Topic 3.4 — Sound Pitch ↔ frequency · loudness ↔ amplitude v ≈ 340 m/s in air
Longitudinal wave — compressions (dark) and rarefactions (light) travel from the loudspeaker.

Oscilloscope trace

Variables

440
0.60
—

Live readouts

Frequency f
440 Hz
Wave speed v
340 m/s
Wavelength λ = v/f
0.77 m
Period T = 1/f
2.27 ms
Audible?
yes (20–20 000 Hz)
Pitch / loudness
mid pitch, medium
Higher frequency → higher pitch (waves closer). Larger amplitude → louder (taller trace). Sound needs a medium.
📋 Measuring the speed of sound (Cambridge)

Echo method: stand a measured distance d from a large wall; clap and start a stopwatch, stop it when you hear the echo. The sound travels 2d in time t, so v = 2d/t. Repeat and average.

Two-microphone / oscilloscope method: place two microphones a distance d apart connected to a double-beam oscilloscope; measure the time delay between the traces; v = d/t.

Sound is a longitudinal wave — particles vibrate parallel to the direction of travel, producing compressions and rarefactions. It cannot travel through a vacuum.

🎯 Syllabus reference (0625)
  • 3.4 Sound — describe sound as a longitudinal wave; state the audible range (20 Hz–20 kHz); relate pitch to frequency and loudness to amplitude; describe methods to measure the speed of sound in air (≈ 330–350 m/s); state that sound requires a medium and travels faster in solids than in liquids than in gases.

Ask the lab assistant