Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Linked equation: v = fλ
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Aim
To measure the frequency, wavelength and speed of waves in a ripple tank and waves on a stretched string.
Method
- Ripple tank: use a lamp above the tank to project the wave pattern onto paper below.
- Measure across 10 waves with a ruler and divide by 10 to find the wavelength.
- Count the waves passing a point in 10 seconds and divide by 10 to find the frequency.
- String: a vibration generator (connected to a signal generator) vibrates a string stretched over a pulley by hanging masses. Adjust the frequency until a clear standing wave appears.
- Measure the length of several loops; one wavelength = two loops. Read the frequency from the signal generator.
- Calculate wave speed: v = f × λ.
| Measured | Frequency (Hz) and wavelength (m) |
| Calculated | Wave speed (m/s) = frequency × wavelength |
| Control variables | Depth of water (ripple tank); tension and type of string |
Questions
Q1 (F) Describe how to measure the wavelength of water waves in a ripple tank.
Show answer
Shine a lamp through the tank onto paper below to see the waves. Use a ruler to measure the distance across 10 waves, then divide by 10.
Q2 (F) Why measure across 10 waves rather than just one?
Show answer
One wavelength is small and hard to measure accurately. Measuring across 10 and dividing reduces the uncertainty, giving a more accurate value.
Q3 (F) 40 waves pass a point in 10 seconds. Calculate the frequency.
Show answer
Frequency = waves per second = 40 ÷ 10 = 4.0 Hz
Q4 (F) Water waves have a frequency of 4.0 Hz and a wavelength of 0.020 m. Calculate their speed.
Show answer
F: v = f λ
I: v = 4.0 × 0.020
A: 0.080 m/s
Q5 (F/H) Ten waves measure 12 cm across. The frequency is 5.0 Hz. Calculate the wave speed in m/s.
Show answer
Wavelength = 12 ÷ 10 = 1.2 cm = 0.012 m
F: v = f λ
I: v = 5.0 × 0.012
A: 0.060 m/s
Q6 (F/H) A standing wave on a string has 4 loops along 1.6 m of string. The signal generator is set to 50 Hz. Calculate the wave speed.
Show answer
One loop = 1.6 ÷ 4 = 0.40 m; one wavelength = two loops = 0.80 m
F: v = f λ
I: v = 50 × 0.80
A: 40 m/s
Q7 (F/H) State one hazard in the ripple tank practical and how to reduce the risk.
Show answer
Water and electricity together – keep the power supply away from the water and wipe up spills straight away. The lamp gets hot – don’t touch it.
Q8 (H) Why might you take a photo of the ripple pattern, or use a strobe light?
Show answer
It “freezes” the moving waves, so the wavelength can be measured more easily and accurately (include a ruler in the photo for scale).
