Question

what is a critical angle

Answer 1

the angle of incidence beyond which rays of light passing through a denser medium to the surface of a less dense medium are no longer refracted but totally reflected.

Answer 2

.CRITICAL ANGLE -WHEN A RAY OF LIGHT PASSES FROM A MEDIUM OF HIGHER OPTICAL DENSITY TO A MEDIUM OF LOWER OPTICAL DENSITY ,THE ANGLE OF INCIDENCE AT WHICH THE ANGLE OF REFRACTION BECOMES 90° IS THE CRITICAL ANGLE.