Transmission & Reflection of Waves (Edexcel International A Level Physics)

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Lindsay Gilmour



Transmission & Reflection of Waves

  • When waves are incident on the interface between two different media, they are either transmitted or reflected
    • 'Incident on' simply means 'to meet'
    • The interface is also called the boundary between media
    • Transmitted means to pass through


  • When the media have similar densities the energy of the wave is mostly transmitted
  • When the media have different densities most of the energy is reflected

Reflected waves in use

  • Uses of reflected waves include:
    • Medical x-rays
    • Sonar
    • Ultrasound scans

Transmitted waves in use

  • In the above examples the waves have to be transmitted through one medium first, before they are reflected
    • X-rays are transmitted through soft tissue
    • Sonar is transmitted through air or water
    • Ultrasound is transmitted through a gel of similar density to the skin so that it reaches the tissues inside the body



  • Reflection occurs when:

A wave hits a boundary between two media and does not pass through, but instead stays in the original medium

  • The law of reflection states:

The angle of incidence = The angle of reflection

Reflection, downloadable IGCSE & GCSE Physics revision notes

Reflection of a wave at a boundary

  • Some of the wave may also be absorbed or transmitted
    • Echos are examples of sound waves being reflected off a surface

  • Flat surfaces are the most reflective
    • The smoother the surface, the stronger the reflected wave is

  • Rough surfaces are the least reflective
    • This is because the light scatters in all directions

  • Opaque surfaces will reflect light which is not absorbed by the material
    • The electrons will absorb the light energy, then reemit it as a reflected wave


  • Transmission occurs when:

A wave passes through a substance

  • For light waves, the more transparent the material, the more light will pass through
    • Transmission can involve refraction but it is not exactly the same
    • For the process to count as transmission, the wave must pass through the material and emerge from the other side
  • When passing through a material, waves are usually partially absorbed
    • The transmitted wave may have a lower amplitude because of some absorption
      • For example, sound waves are quieter after they pass through a wall

      Transmission of wave, downloadable IGCSE & GCSE Physics revision notes

      When a wave passes through a boundary it may be absorbed and transmitted

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.

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