Investigating Sound with the PASCO Sound Sensor and a Sonometer

 One of the joys of teaching physics in a fully equipped lab is being able to see and measure what we normally only hear.

This week I’ve been running experiments using the PASCO Sound Sensor alongside a traditional sonometer – and it’s a wonderful blend of old-school apparatus and modern digital analysis.

I still find it exciting when students see a waveform appear on screen that corresponds perfectly to a vibrating string in front of them.

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🎻 The Classic Sonometer Experiment

A sonometer consists of:

• A wooden resonance box

• A stretched wire (or string)

• A movable bridge

• Hanging masses to control tension

It’s traditionally used to investigate how the frequency of a vibrating string depends on:

$$f = \frac{1}{2L}\sqrt{\frac{T}{\mu}}$$

Where:

• $f$ = frequency

• $L$ = vibrating length

• $T$ = tension

• $\mu$ = mass per unit length

For GCSE and A-Level students, this equation beautifully links waves, forces and material properties.

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🔊 Bringing It to Life with the PASCO Sound Sensor

Using the PASCO Sound Sensor connected to Capstone, students can:

✅ Measure frequency directly
✅ Display real-time waveforms
✅ Analyse harmonics
✅ Compare theoretical and measured values

Instead of relying purely on tuning forks or matching by ear (as we did decades ago), students can now:

• Change the tension

• Adjust the string length

• Watch the frequency change instantly on screen

It transforms a qualitative experiment into a powerful quantitative investigation.

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🧪 Experiment Ideas

1️⃣ Frequency vs Length

Keep tension constant.
Measure frequency as length changes.
Plot $f$ against $\frac{1}{L}$.
You should get a straight line.

2️⃣ Frequency vs Tension

Keep length constant.
Vary hanging masses.
Plot $f$ against $\sqrt{T}$.

3️⃣ Investigating Harmonics

Lightly touch the string at midpoint.
Observe the doubling of frequency (second harmonic).

Seeing the waveform change in real time makes harmonics much easier to understand.

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🎥 Why I Love This Experiment

In my Hemel Private Tuition lab and TV studio setup, I can:

• Film the vibrating string close-up

• Overlay the live waveform

• Zoom into frequency analysis

• Let online students analyse the data remotely

At £40 per session, students aren’t just watching — they’re interacting with real experimental data.

This is where traditional physics meets modern technology.

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🧠 What Students Learn

✔️ Wave properties
✔️ Experimental design
✔️ Graph analysis
✔️ Evaluating uncertainties
✔️ Linking theory to measurement

And perhaps most importantly…
They realise physics is something you can see and measure, not just equations in a textbook.

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🌍 Blog Closing Thought

From a wooden resonance box to digital spectral analysis — it’s remarkable how far school physics has come.

Yet the principle remains beautifully simple:

A vibrating string, under tension, produces a frequency that obeys precise physical laws.

And now we can measure it in milliseconds.