total internal reflection
Overview
This lesson explores the phenomenon of total internal reflection (TIR), which occurs when light travels from a denser to a less dense medium at a sufficiently large angle. We will also examine the critical angle and its relationship to TIR, and then apply these principles to understand the operation of optical fibres.
Understanding Refraction and Snell's Law
Before delving into Total Internal Reflection, it's crucial to recap refraction. Refraction is the bending of light as it passes from one medium into another, caused by a change in the light's speed. When light travels from a less dense medium (e.g., air) to a denser medium (e.g., glass), it bends t...
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Key Concepts
- Refraction: The bending of light as it passes from one medium to another due to a change in speed.
- Critical Angle (c): The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90 degrees.
- Total Internal Reflection (TIR): The complete reflection of a light ray at the boundary between two media, occurring when the angle of incidence exceeds the critical angle and light travels from a denser to a less dense medium.
- Optical Fibre: A thin, transparent fibre, usually made of glass or plastic, that transmits light signals over long distances using total internal reflection.
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Exam Tips
- →Always state both conditions for Total Internal Reflection (TIR) when asked: light from denser to less dense medium AND angle of incidence greater than critical angle.
- →Be prepared to derive the formula for the critical angle (sin c = n2/n1) using Snell's Law, and ensure you correctly identify n1 as the refractive index of the denser medium and n2 as the less dense medium.
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