# Critical angle

The critical angle is the angle of incidence above which total internal reflection occurs. If the speed of light is $$1.5 \times 10^8\text{ m/s}$$ in a particular medium, then what is the critical angle of the light passing through this medium into the air?

The speed of light in the air is $$3.0 \times 10^8\text{ m/s}.$$

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