What occurs when light hits the core of a fiber optic at an angle smaller than the critical angle?

When light hits the core of a fiber optic at an angle smaller than the critical angle, total internal reflection does not occur. Instead, some portion of the light will refract into the surrounding cladding, which is of a lower refractive index than the core. This is because the critical angle is specifically defined as the minimum angle of incidence at which total internal reflection can occur; if the angle is smaller than this critical value, the light cannot be completely reflected back into the core.

In this scenario, rather than all energy being reflected, part of the light transmits into the cladding, resulting in a loss of intensity due to some light escaping the core. This process can lead to signal degradation and can affect the efficiency of light transmission through the fiber. Therefore, the correct understanding is that when light strikes at an angle less than the critical angle, not all energy is reflected—some is lost to refraction, enabling propagation into the cladding rather than back into the core.