Refraction through a semicircular block (including TIR)
I can describe and explain when refraction happens and when total internal reflection happens at boundaries between media.
Refraction through a semicircular block (including TIR)
I can describe and explain when refraction happens and when total internal reflection happens at boundaries between media.
Lesson details
Key learning points
- At a boundary to a medium where the wave speed increases, waves are refracted away from the normal.
- If the angle of incidence is too big (bigger than the critical angle) the waves will undergo total internal reflection.
- The critical angle is the greatest angle of incidence before total internal reflection occurs.
- For a glass–air boundary, the critical angle (c) is about 42°.
Common misconception
Pupils sometimes rote-learn what specific examples of refraction look like, rather than developing a more general understanding of the direction waves turn based on changes in wave speed.
Teach pupils the general theory of refraction and apply it to a variety of different examples where wave speed changes (e.g. sound waves refract in the opposite direction to light at an air-glass boundary due to the different wave speeds).
Keywords
Refraction - Refraction occurs when waves travel from one transparent medium to another, causing a change in direction.
Medium - A medium is the material through which a wave is travelling.
Angle of incidence - The angle of incidence is the angle between the incident ray and the normal.
Total internal reflection - Total internal reflection is when waves fully reflect from a boundary to a medium when greater wave speed, rather than being transmitted through.
Critical angle - The critical angle is the greatest angle of incidence before total internal reflection occurs for a boundary to a medium with greater wave speed.
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Starter quiz
6 Questions
reflected ray
refracted ray
incident ray
angle of reflection
angle of incidence
angle of refraction
Exit quiz
6 Questions
The beam passes through the boundary without refracting or reflecting.
The refracted beam travels into the air.
The refracted beam travels along the boundary between water and air.
The beam is totally internally reflected (back into the water).