AQA GCSE Physics

Revision Notes

6.1.7 Reflection, Absorption & Transmission

Reflection, Absorption & Transmission

  • Depending on the densities of the materials on either side of a boundary, a wave may be:
    • Reflected
    • Transmitted
    • Absorbed

Reflection

  • 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

  • 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 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

Absorption

  • Absorption occurs when:

Energy is transferred from the wave into the particles of a substance

  • Waves can be partially or completely absorbed
    • Sound waves are absorbed by brick or concrete in houses
  • Light will be absorbed if the frequency of light matches the energy levels of the electrons
    • The light will be absorbed, and then reemitted over time as heat
  • If an object appears red, this means:
    • Only red light has been reflected
    • All the other frequencies of visible light have been absorbed

Absorption, downloadable IGCSE & GCSE Physics revision notes

The object is seen as red since the red light is reflected whilst the other colours are absorbed

Reflection Ray Diagrams

  • Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
    • The angle of the wave approaching the boundary is called the angle of incidence (i)
    • The angle of the wave leaving the boundary is called the angle of reflection (r)
  • The law of reflection states that these angles are the same:

Angle of incidence (i) = Angle of reflection (r)

Wave Reflection, downloadable IGCSE & GCSE Physics revision notes

Reflection of a wave at a boundary

  • When drawing a ray diagram an arrow is used to show the direction the wave is travelling
    • An incident ray has an arrow pointing towards the boundary
    • A reflected ray has an arrow pointing away from the boundary
  • The angles of incidence and reflection are usually labelled i and r respectively

Exam Tip

When drawing ray diagrams, a simple line with an arrow is enough to represent the wave.

You do not need to draw the wavefronts unless asked to do so!

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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