Critical angle (θc)

Definition

The critical angle is defined as the minimum angle of incidence at which total internal reflection occurs. It is determined by comparing the indices of refraction between two media.

Analogy

Think about trying to skip a stone on water. If you throw it at too shallow an angle, it will sink into the water. But if you throw it at just the right angle, it will bounce off and stay above water. This "just right" angle is similar to the critical angle where total internal reflection happens.

Related terms

Total Internal Reflection: When all incident light rays are reflected back inside a medium due to hitting an interface at an angle greater than or equal to the critical angle.

Index of Refraction: A measure indicating how much slower light travels through a particular medium compared to vacuum or air.

Optic Fiber: A thin strand made out of glass or plastic that uses total internal reflection to transmit light signals over long distances.