Ripple Tank (Cambridge (CIE) O Level Physics): Revision Note

Investigating Waves with a Ripple Tank

• Ripple tanks are commonly used in experiments to demonstrate the following properties of water waves:

  • Reflection at a plane surface

  • Refraction due to a change in speed caused by a change in depth

  • Diffraction due to a gap

  • Diffraction due to an edge

 Ripple Tank Apparatus

Reflection, refraction and diffraction can be demonstrated using a ripple tank

Investigating Reflection

• Reflection can be shown by the waves hitting a plane (straight) surface, such as a wall or mirror

Reflection in a Ripple Tank

Investigating Refraction

• Refraction can be shown by placing a glass block in the tank

  • The glass block should sit below the surface of the water and cover only some of the tank floor

• The depth of water becomes shallower here the glass block is placed

  • Since speed depends on depth, the ripples slow down when travelling over the block

• This is a good model of refraction showing how waves slow down when passing from deep water into shallow water

Refraction in a Ripple Tank

When water waves travel from deep areas to shallow areas they slow down

Investigating Diffraction

• Diffraction can be shown in a ripple tank by placing small barriers and obstacles in the tank

• As the water waves encounter two obstacles with a gap between them, the waves can be seen to spread out as follows:

Diffraction through a Gap in a Ripple Tank

Diffraction of water waves through a gap

• As the water waves encounter the edge of an obstacle, the waves can be seen to spread out as follows:

Diffraction round an Edge in a Ripple Tank

Diffraction of water waves after passing an edge

• The amount of diffraction depends on the size of the gap compared to the wavelength of the water wave

• The diagram below shows how the wavelengths differ with frequency in a ripple tank

  • The higher the frequency of the motor, the shorter the wavelength

  • The lower the frequency of the motor, the longer the wavelength

Generating Waves in a Ripple Tank

Ripple tank patterns for low and high frequency vibration