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CAIE IGCSE Physics 3.2.2.4 Meaning of Critical Angle Questions

Practise stating the critical angle clearly and recognising it on diagrams where a ray in a denser medium reaches a boundary.

Syllabus
2026–2028
Course
Physics 0625

Exam points

  • Distinguish scalars from vectors by direction and classify common physics quantities.

CAIE IGCSE Physics 3.2.2.4 Meaning of Critical Angle Questions question 1

[Maximum number: 2]

Fig. 5.1 shows a block ABCD made of glass that has a refractive index of 1.5. The block has one curved side AB and three straight sides, BC, CD and DA.

Fig. 5.1

Fig. 5.1

There are right angles at C and D. The curved side AB is one quarter of the circumference of a circle that has its centre at point P.

A ray of monochromatic light enters the block through the curved side AB and strikes side BC at P. Some light emerges into the air and some is reflected.

Fig. 5.1 shows that the angle between the ray of light and line AP is θ\theta, where line AP is at right angles to side BC.

Angle θ\theta increases to 45∘45^{\circ}.

State and explain what happens to the light that strikes P .

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