Required practical

Measure the frequency, wavelength and speed of waves in a ripple tank

A ripple tank can be used to measure and calculate frequency, wavelength and the speed of waves on the surface of the water it contains. It is a transparent shallow tray of water, with a light shining down through it onto a white card below, to more easily see the motion of the ripples created on the water’s surface. Ripples can be made by hand but to generate regular ripples it is better to use a motor.

Formula triangle demonstrating v equals f times lambda. V at the apex of triangle, f in bottom-left corner and lambda in bottom-right. Also demonstrates f equals v over lambda, lambda equals v over f.

Aim of the experiment

To measure the frequency, wavelength and speed of waves in a ripple tank.

A ripple tank, on a table, with surrounding equipment including a lamp, power supply, motor and wooden beam supported by elastic bands.

Method

  1. Set up the ripple tank as shown in the diagram with about 5 cm depth of water.
  2. Adjust the height of the wooden rod so that it just touches the surface of the water.
  3. Switch on the lamp and motor and adjust until low frequency waves can be clearly observed.
  4. Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take your measurements from the still picture.
  5. Count the number of waves passing a point in ten seconds then divide by ten to record frequency.
  6. Calculate the speed of the waves using: wave speed = frequency × wavelength.

Results

Here is an example of how the results table could look:

Lengths of 12 waves (cm)Wavelength (cm)Number of waves in 10 secondsFrequency (Hz)Wave speed (cm/s)
...............

Analysis

State the frequency, wavelength and speed of waves measured in this ripple tank.

Hazards and control measures

HazardConsequenceControl measures
Electrical components near waterShock, damage to goodsSecure electrical components before adding water taking care not to splash