Edexcel IGCSE Physics 3.21 Critical Angle Questions

The critical angle is the angle of incidence in the higher-index medium that makes the refracted ray travel along the boundary at 90°. At larger incident angles, total internal reflection occurs.

Exam points

determine the critical angle from a prism ray diagram using the boundary geometry
explain c as the incident angle in the denser medium giving refraction at 90°
predict whether a ray refracts out or totally internally reflects for a given c

[Maximum number: 2]

This question is about refraction.

The torch is moved below the surface of the water. Light from the torch is incident on the water surface at an angle greater than the critical angle.

Explain the meaning of the term critical angle.

You may draw a diagram to help your answer.

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Edexcel IGCSE Physics 3.21 Critical Angle Questions question 1