When a ray of light passes through the principal focus of a convex lens, it emerges on the other side parallel to the principal axis. The convex lens is thicker at the center, causing incoming parallel rays to converge at its principal focus. Upon refraction, the ray bends toward the center of the lens and, if extended backward, appears to converge at the principal focus. This behavior is essential in understanding the converging nature of convex lenses, exploited in various optical devices like magnifying glasses and cameras. The parallel emerging ray is a key outcome and a fundamental principle in lens optics.