Total Internal Reflection (Pure Only)

To ensure that ray entering the block from the curved surface does not bend → light ray is always directed towards centre of the glass blocks diameter

Investigating Total Internal Reflection
	When light ray crosses both boundaries perpendicularly → there is no change in the ray’s direction
	As the ray box is moved clockwise → there is refraction and partial reflection
	As the ray box continues to move clockwise → at a particular angle of incidence ${\theta }_c$, the angle of refraction becomes $90°$ ${\theta }_c$ is known as the critical angle
	When the angle of incidence in the glass block is greater than ${\theta }_c$, the ray will be reflected off the flat surface of the block. There is no refraction.
	Using this figure → we can summarise that: - between A and B → the ray undergoes refraction with some reflection - at B → the angle of refraction is $90°$ and the angle of incidence ${\theta }_c$ is known as the critical angle - between B and C → the incident ray undergoes total internal reflection

Definition

Critical Angle ${\theta }_c$ is defined as the angle of incidence in an optically denser medium for which the angle of refraction in the less dense medium is $90°$

Definition

Total Internal Reflection is the complete reflection of a light ray in an optically denser medium at the boundary with an optically less dense medium

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2 conditions for total internal reflection to occur:

• Incident ray must travel from an optically denser medium to an optically less dense medium
• Angle of incidence must be greater than the critical angle

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there is a relationship between the critical angle and the refractive index n for a medium

• for a glass block surrounded by air → formula for its refractive index n in terms of the critical angle ${\theta }_c$ can be derived as follows:

Formulae

the angle of refraction is $90°$ when the angle of incidence in the glass block is $thet{a}_c$. Applying the principle of reversibility: $n=\frac{sini}{sinr}=\frac{1}{sin{\theta }_c}$

Formulae

Calculate Critical Angle:

• $sin{\theta }_c=\frac{n_2}{n_1}$

• where $n_1$ is refractive index of denser medium

• and $n_2$ is the refractive index of the less dense medium

Periscope Orientation

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Application of Total Internal Reflection

Application of Total Internal Reflection

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Sample

when answering questions, make sure to state how light is travelling from optically denser medium to optically less dense medium

Note

some light is always partially reflected