The critical angle is the minimum angle of incidence at which light is totally internally reflected within a medium. It occurs when light passes from a medium with a higher refractive index to one with a lower refractive index.
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The critical angle can be calculated using the formula $\theta_c = \sin^{-1}(\frac{n_2}{n_1})$, where $n_1$ and $n_2$ are the refractive indices of the initial and second medium, respectively.
Total internal reflection only occurs when the incident angle is greater than or equal to the critical angle.
As the difference between refractive indices increases, the critical angle decreases.
No refraction occurs at angles equal to or greater than the critical angle; all light is reflected back into the original medium.
The concept of critical angle is applied in optical fibers to keep light signals contained within the fiber.
Review Questions
What happens to light when it hits an interface at an angle equal to or greater than the critical angle?
How does the critical angle change if you increase the refractive index of the initial medium?
Write down and explain how you would use Snell's Law to derive the formula for calculating the critical angle.
A phenomenon where all incident light is reflected back into a medium when it hits an interface at an angle greater than or equal to the critical angle.