Long answer·Hard exam skill (4/5)·Calculator allowed
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
An optical fibre has core refractive index and cladding refractive index . For a ray incident from core to cladding, find the critical angle and state the condition for guiding by total internal reflection.
Total: 5 marks
(a) Find the critical angle at the core-cladding interface. (3 marks)
(b) State the condition on the internal angle of incidence for guiding. (2 marks)
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