Question

Can total internal reflection occur when light travels from a rarer to a denser medium?

Answer 1

Total internal reflection cannot take place when light moves from a rarer medium to a denser medium because the angle of refraction is always less than the angle of incidence. Even if the incidence angle is 90°, the refracted ray still emerges with an angle less than 90°. Hence, total internal reflection is not possible when light travels from a rarer to a denser medium.