Optical Fibres
2 marks · EasyExplain why light is able to travel through a curved optical fibre without escaping.
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Also accept: Light always hits the core–cladding boundary at an angle greater than the critical angle, so it undergoes total internal reflection and stays inside.
Common mistakes: Not mentioning total internal reflection; Confusing refraction with reflection
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Marking points
M1 · 1 mark · States that total internal reflection occurs at the core–cladding boundary.
A1 · 1 mark · Links to curved fibre: angle always greater than critical angle so light stays inside.
Worked solution
In an optical fibre, the light always hits the boundary at an angle greater than the critical angle, so it is totally internally reflected. Even when the fibre bends, this still happens so the light remains inside.