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CAIE IGCSE Physics 3.2.2.8 Critical angle relation: n = 1 / sin c

Practise applying n = 1 / sin c to connect refractive index with critical angle and total internal reflection.

Syllabus
2026–2028
Course
Physics 0625

Exam points

  • use n = 1 / sin c to calculate refractive index or critical angle
  • interpret when a boundary angle reaches the critical angle for internal reflection

3.2.2.8—Critical angle relation: n = 1 / sin c question 1

[Maximum number: 2]

Fig. 5.1 shows four rays of red light, P, Q, R and S, coming from a spotlight in a swimming pool.

Fig. 5.1

Fig. 5.1

The angle of incidence for ray R is 49∘49^{\circ}.

Calculate the refractive index of the water.
refractive index =

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