Ripple Tank (CIE IGCSE Physics)

• 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

 

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

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

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 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 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

Ripple tank patterns for low and high frequency vibration