AQA GCSE Physics · Waves
Waves required practical
Measure the frequency, wavelength and speed of waves in a ripple tank and of waves on a stretched string.
A vibration generator makes a string vibrate in a standing wave. You measure the wavelength with a metre ruler, read the frequency from the signal generator, and calculate speed with v = f × λ.
Equipment
- Vibration generator and signal generator
- String or elastic cord, a pulley and a mass hanger with masses
- Wooden bridge and metre ruler
- Ripple tank with a lamp, motor and paddle (for water waves)
- Stopwatch (for counting water waves)
Variables
- Independent you change
- Frequency of the signal generator
- Dependent you measure
- Wavelength of the wave
- Control you keep the same
- Same string and tension (same masses)
- Same length between the bridge and pulley
Method
- 1
Attach the string to the vibration generator, pass it over a pulley and hang masses on the end to keep it taut.
- 2
Turn on the signal generator and adjust the frequency until a clear standing wave appears.
- 3
Use a metre ruler to measure across as many half-wavelengths (loops) as possible, then work out one wavelength.
- 4
Read the frequency from the signal generator.
- 5
Calculate the wave speed using v = f × λ.
- 6
Ripple tank: count the waves passing a point in 10 s for frequency, and measure across 10 waves on the shadow for wavelength.
Worked example
A string at 80 Hz, and water waves in a ripple tank.
| Wave | Frequency (Hz) | Wavelength (m) | Speed (m/s) |
|---|---|---|---|
| String: 4 loops across 1.20 m | 80 | 0.60 | 48 |
| Ripple tank: 10 waves across 15 cm | 12 | 0.015 | 0.18 |
Working
String: 4 loops = 2 wavelengths = 1.20 m, so λ = 0.60 m
v = f × λ = 80 × 0.60 = 48 m/s
Ripple tank: λ = 0.15 m ÷ 10 = 0.015 m; v = 12 × 0.015 = 0.18 m/s
Conclusion
Waves on the string travel at about 48 m/s and the water waves at 0.18 m/s. For the same string and tension the speed stays the same, so raising the frequency makes the wavelength shorter.
Risks
- Masses could fall if the string snapsKeep feet clear and don’t overload the hanger.
- Water near the ripple tank’s electrical supplyKeep the lamp and power supply dry; mop up spills.
- Strobe lights can trigger seizuresCheck for photosensitive epilepsy before using a strobe.
Common mistakes
- Measuring one loop as a full wavelength. One loop is half a wavelength.
- Measuring a single wave. Measure across several waves and divide, to reduce uncertainty.
- Forgetting to convert cm to m before using v = f × λ.
Better results
- Measure across as many wavelengths as possible and divide, for a more precise wavelength.
- Use a strobe or take a photo of the ripple tank to “freeze” the waves before measuring.
- Repeat for several frequencies and take a mean speed.
Launching November 2026
7 exam questions on this practical.
Practise the method, the variables, the maths and what the results mean, then revise the Waves flashcards. It opens to students soon: join the waitlist and we’ll email you once, when it does.