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Waves 6. Comparing the terms reflection, refraction, diffraction, transmission, absorption

GCSE level Physics exam revision notes on waves

Introduction to waves: 6. More on the general properties of any waves - a basic introduction to their reflection, refraction, diffraction and absorption

[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

6. More on the general properties of any waves - reflection, refraction, diffraction

The need for a scientific model of waves and their behaviour.

(all dealt with in more details for specific examples like light or sound)

All waves undergo reflection, refraction and diffraction and a general description of them is explained below.

Appreciate and understand that all three wave effects can be successfully modelled in the way described in the manner described below and predictions can be made on the basis of these models.

 

What can happens when waves meet a boundary between two media?

When waves meet an interface between two materials there are three possible outcomes.

The outcome depends on the properties of the wave and the nature of the two materials involved.

 

(a) The wave, its energy, is absorbed by the second material, so the energy store of the 2nd material is increased - this usually equates to increasing the thermal energy store of the 2nd material.

Soft materials easily absorb sound wave energy.

Rough matt black surfaces absorb most of visible light that's why they look black!

Infrared radiation from the Sun heats up surfaces.

 

(b) The wave is reflected back off the second material without losing any significant energy. In this case there is little wave energy absorbed or transmitted.

If the surface is particularly smooth-shiny and flat, very little wave energy is absorbed and you can observe a high quality reflected image e.g. looking at yourself in a silver surfaced mirror!

In the case of sound you get echoes.

If the surface is rough, much of the wave energy is absorbed or scattered in all directions.

 

(c) The wave is transmitted through the second material without being absorbed and the waves may change direction (refraction).

This can happen if the material is transparent and the waves can continue passing through the 2nd material

You see this by the 'bent' image at the 'wrong' angle when observed putting a stick in water.

Refraction effects are used in the lenses of optical equipment like reading glasses and cameras.

 

(d) There are situations where waves partially meet a barrier and bend round corners or pass through a gap in a barrier and then spread out - radiating from the gap.

These effects are called diffraction and does not involve passing from one medium to another.

You can hear sound round a corner - that's due to a combination of reflection and diffraction effect.

 

(e) You should be aware that in some situations (some already mentioned) you may get a combination of effects.

e.g. when a light beam in air then passes through a glass block, some rays refract at the interface and others are reflected.

What actually happens at an interface depends on the wavelength/frequency of the wave and the properties of the materials the waves strike.

 

(f) In some cases, most, if not all, of the waves energy is absorbed by a barrier.

e.g. a black matt surface absorbs most of visible light.

Soft sound proofing material in ear defenders absorbs much of the externally produced sound wave energy.

The nature and extent of absorption is very dependent on the nature of the wave and the material the wave impacts on.

 

The five points (a) to (e) are discussed in detail using the scientific models of waves in further sections.

There are separate sections on sound waves, see ...

Sound waves, properties explained, speed measure, uses of sound, ultrasound, infrasound, earthquake waves.

 

INDEX notes: Investigating and introducing the properties of waves

Key points Introduction to waves: Distinguishing the properties of waves in terms of reflection, refraction, diffraction, transmission and absorption

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 explaining the wave interactions: reflection, refraction, diffraction, transmission, and absorption, aligned with the core requirements across major UK GCSE/IGCSE exam boards (WJEC, CCEA, CIE, AQA, Edexcel, OCR). These concepts are essential for understanding how waves behave at boundaries and in different media.

Wave Interactions: Summary Revision Notes

1. Reflection of waves

  • Definition: When a wave bounces off a surface or boundary instead of passing through.
  • Law of Reflection:
    Angle of incidence = Angle of reflection
  • Examples:
    • Light reflecting off a mirror
    • Sound echoing off a wall
  • Types:
    • Specular (smooth surface, clear reflection)
    • Diffuse (rough surface, scattered reflection)

2. Refraction of waves

  • Definition: When a wave changes direction due to a change in speed as it crosses a boundary between two media.
  • Key Effects:
    • Bending towards the normal when entering a denser medium
    • Bending away from the normal when entering a less dense medium
  • Examples:
    • Light bending when entering glass from air
    • Water waves slowing in shallow water
  • Note: Frequency stays the same; speed and wavelength change

3. Diffraction of waves

  • Definition: The spreading out of waves when they pass through a gap or around an obstacle.
  • Key Factors:
    • More noticeable when wavelength ≈ gap size
  • Examples:
    • Sound bending around corners
    • Water waves spreading after passing through a narrow opening

4. Transmission of waves

  • Definition: When a wave passes through a material or boundary.
  • Examples:
    • Light passing through glass
    • Sound travelling through walls
  • Note: May involve partial reflection and refraction

5. Absorption of waves

  • Definition: When wave energy is taken in by the material, often converting to heat.
  • Examples:
    • Dark surfaces absorbing light
    • Foam absorbing sound
  • Effect: Reduces wave amplitude and energy

 Student Tips about waves

  • Use ray diagrams to visualise reflection and refraction.
  • Practise identifying wave behaviour at boundaries.
  • Remember: Only diffraction increases with wavelength.
  • Link concepts to real-world applications (e.g. fibre optics, ultrasound, noise insulation).
  • Review required practicals involving ripple tanks and light boxes.

Common Misconceptions about waves

  •  “Refraction changes frequency.”
     Frequency stays the same; speed and wavelength change.
  •  “Diffraction only happens with sound.”
     All waves can diffract - light, water, and radio included.
  •  “Transmission means no energy loss.”
     Some energy may be reflected or absorbed.
  •  “Reflection only happens with mirrors.”
     All waves can reflect - sound, water, and light.

Keywords, phrases and learning objectives for comparing the terms reflection, refraction, diffraction, transmission, absorption in the context of waves

Know that when waves meet a surface or boundary they may be reflected, refracted, diffracted, absorbed or transmitted, and sometimes several things go on at the same tome!

Appreciate the need for a scientific model to explain the behaviour of waves.

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INDEX notes: Investigating and introducing the properties of waves

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