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School-college Physics Notes: Waves 7. Reflection model of waves

GCSE level Physics exam revision notes on waves

Introduction to waves: Part 7. REFLECTION of waves and a scientific wave model diagram

[Author © Dr Phil Brown PhD: Doc Brown's physics exam revision notes suitable for students of UK IGCSE & GCSE level physics courses, ~ US grades 9-10 physics [waves-intro- page updated Mar 31st 2026 *]

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[KEY POINTS and learning objectives for this page, after initial notes]

INDEX physics notes: Investigating & introducing properties of waves

7. REFLECTION of waves and a scientific wave model

Theoretical model of a reflected wave.

  • Waves are readily reflected off smooth flat surfaces e.g. light reflected off a mirror.

  • Reflection of waves at a smooth surface (e.g. light)

    • The vertical dotted line is called the 'normal', it isn't a ray, but helps in the construction and interpretation of ray diagrams. A plane mirror means one of a perfectly flat surface.

    • Angle 2 = angle of incidence of the incident ray.

    • Angle 3 = angle of reflection of the reflected ray.

    • Angle 2 = Angle 3 - the simple 'law of reflection'

    • Angle 1 = angle 4.

    • All angles are measured with respect to the 'normal' which is at 90o to the surface - the dotted line.

    • the 'normal' is an imaginary line at 90o to a surface or a boundary between two media (see refraction below) at a point where the waves are hitting. It is useful when constructing ray diagrams (like the one above) to show the paths of the ways and their angles relative to the surface or boundary.

  • The scientific wave model of reflection.

    • Think of the wavefronts as the crests of the waves e.g. as you observe ripples on water or waves at the seaside.

    • When the waves meet the flat smooth surface they are 'bounced' off symmetrically at the same angle with respect to the normal - see the first reflection diagram.

    • You can readily see this with ripple tank experiment waves - just put a barrier in their way at 45o to their direction and the wave direction is changed by 90o.

    • Similarly you will see the same with light ray experiments using ray box.

INDEX notes: Investigating and introducing the properties of waves

Key points Introduction to waves: A model of wave reflection at a solid surface

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE physics 9-1 level science examinations

A structured set of summary revision notes on a model to explain the reflection of waves at any surface, aligned with the core requirements across major UK GCSE/IGCSE exam boards (WJEC, CCEA, CIE, AQA, Edexcel, OCR). This model helps students visualise and predict wave behaviour at boundaries - essential for mastering wave physics.

Reflection of Waves: Conceptual Model

Core Principle

Reflection occurs when a wave hits a boundary and bounces back into the original medium. The behaviour is governed by the Law of Reflection:

Angle of incidence  = Angle of reflection

Reflection Model Components

Component Description
Incident ray The incoming wave approaching the surface
Reflected ray The wave bouncing off the surface
Normal line A line drawn perpendicular to the surface at the point of incidence
Angles Measured between rays and the normal, not the surface
Surface type Determines reflection type: specular (smooth) or diffuse (rough)

Required Wave Reflection Practical (Ripple Tank or Ray Box)

Students investigate reflection by:

  • Shining light at a mirror or waves at a barrier
  • Measuring angles using a protractor
  • Verifying ( i = r )
  • Observing specular versus diffuse reflection

Real-World Examples of reflected waves

  • Light reflecting off a mirror (specular)
  • Sound echoing off a wall (diffuse)
  • Water waves bouncing off a barrier in a ripple tank

Typical Exam Board Coverage of wave reflection model

Reflection Model Required Practical
 Law of reflection, ray diagrams  Ray box, ripple tank, ray diagrams
 Specular versus diffuse reflection  Light reflection, ray diagrams
 Wavefront and ray models  Reflection experiment, ray diagrams
 Reflection of light and water  Ripple tank
 Reflection of sound and light  Ray tracing
 Ray diagrams and wavefronts  Light box experiment, ray diagrams

 Student Tips about the reflected wave model

  • Always draw the normal line first when constructing ray diagrams.
  • Use a sharp pencil and ruler for accurate angles.
  • Remember: angles are measured from the normal, not the surface.
  • Practise distinguishing specular versus diffuse reflection in diagrams.
  • Link reflection to applications like mirrors, sonar, and radar.

Common Misconceptions about the model of reflection

  •  “Angles are measured from the surface.”
     They’re measured from the normal.
  •  “Reflection changes wave speed or frequency.”
     Reflection does not change speed, frequency, or wavelength.
  •  “Diffuse reflection breaks the law of reflection.”
     Each ray still obeys ( i = r ); the surface causes scattering.
  •  “Only light reflects.”
     All waves can reflect - sound, water, seismic, etc.

Keywords, phrases and learning objectives for the reflection model of waves

Be able to describe reflection of waves using a scientific wave model and explain wave refraction with suitable diagrams i.e. explain the theoretical modelling of reflected waves.

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INDEX physics notes: Introducing the properties of waves

INDEX of all notes on waves, radiation, astronomy etc.

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INDEX notes: Investigating and introducing the properties of waves

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