4.6.4 Graphical Representations of Transverse & Longitudinal Waves

• Transverse and longitudinal waves can be represented graphically

Transverse Waves

• Transverse waves show areas of crests (peaks) and troughs

Diagram of a transverse wave

• The peaks are the maximum positive displacements
• The troughs are the maximum negative displacements
• The direction of the energy transfer is perpendicular to the direction of vibration of the particles in the wave

Longitudinal Waves

• Longitudinal waves show areas of compressions and rarefactions

Diagram of a longitudinal wave

• The compressions are areas of high pressure due to particles being close together.
• The rarefactions are areas of low pressure due to the particles spread further apart
• The direction of energy transfer is parallel to the direction of vibration of the particles in the wave

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• Waves can also be demonstrated by ripple tanks
  • These produce a combination of transverse and longitudinal waves

Wave effects can be demonstrated using a ripple tank

• In a ripple tank, a motorised wooden straight-edged bar produces plane (straight) waves while a small dipper produces circular waves
• When a light is shone from above, the bright bands seen on the screen below the tank show the wave crests (wavefronts)
  • This makes it possible to measure the wavelength of the water waves and investigate the angles of reflection and refraction

• Reflection can be investigated using plane and curved surfaces, and the angles of incidence and reflection measured with respect to the normal
• Refraction can be investigated using a glass sheet to decrease the water depth and produce a region with a different wave speed
  • If the separation of the wavefronts decreases, this shows they are travelling more slowly and vice versa

• Changing the angle of the wooden bar causes the wavefronts to go in a different direction
  • The ripple tank, therefore, can also be used to study interference and diffraction