AQA GCSE Measuring the speed of ripples on the surface of water

AQA GCSE Measuring the speed of ripples on the surface of the water(Physics)

Measuring the speed of Ripples on the surface of the water

A ripple tank can be used to investigate the speed of ripples on the surface of water.

Ensure the ripple tank is filled with water and switch on the light source above so that light shines downwards through the tank of water, onto a screen below the tank.

Use a wooden ruler to tap the water surface or turn on a vibrating motor to create consistent ripples. Often a motor is attached to the wooden block to generate the waves at a constant frequency. The image below will show what is seen on the screen:

The vertical lines are the wavefronts, distance between the wavefronts are the wavelength. So, each wavelength represents 1 wave.

Place a ruler on the screen beneath the tank and take a photograph of the screen and ruler.

Using the ruler, measure the length of the screen then divide by the number of waves to find the wavelength as shown below.

On the screen above there are 14 waves in total, this is 28 cm long.

Wavelength = 28cm/14 = 2cm or 0.02m

Finding the frequency.

To find the frequency, we will count the number of waves that go past in 10 seconds. Then divide the number of waves counted by 10.

To make this easier, the screen is recorded using a video then played back slowly.

Lets assume in our case that there were 40 waves in 10 seconds. This means that there will be 40/10 = 4Hz.

Frequency = number of waves that pass in 10 seconds/10

Calculate the wave speed

Wave speed = wavelength x frequency

In our case:

Wavelength = 0.02m

Frequency = 4Hz

Wave speed = 0.02 x 4 = 0.08 m/s

Practice Question

1.What can a ripple tank be used for?

2. The following diagram is a diagram of a screen. Use the image below to calculate the wavelength of the wave shown on the screen.

3. The wave that was recorded in the screen above in question two, was investigated for frequency. The student counted 14 waves passing in 10 seconds. Calculate the frequency of this wave

4. Using your answers to questions two and Three, calculate the wave speed of the wave shown on the screen in question 2.