How does total internal reflection occur?

Total internal reflection occurs when a wave traveling in a denser medium approaches a boundary with a less dense medium and hits it at an angle greater than the critical angle. At this critical angle, the wave cannot pass into the less dense medium and instead reflects back entirely into the denser medium. This phenomenon is crucial in various applications, including optical fibers, where light signals are transmitted efficiently by continually undergoing total internal reflection.

In this context, when light travels from a denser to a less dense medium and meets the boundary at an angle exceeding the critical angle, it results in total internal reflection, thereby refracting into the less dense medium is not possible. This principle highlights the relationship between wave speed, angle of incidence, and the optical properties of materials. Understanding this concept aids in grasping the principles of optics and wave behavior in different media, cementing why this is the correct choice.