In total internal reflection, the light travels from

The correct answer is B, denser to rarer medium and it occurs with no loss of intensity. Total internal reflection happens only when light inside a denser medium meets the boundary with a rarer one at an angle larger than the critical angle, and all of the light is reflected back. When light passes from a denser medium such as glass or water into a rarer one such as air, it bends away from the normal. As the angle of incidence grows, the refracted ray bends further until, at the critical angle, it grazes the surface. Beyond that angle no light escapes; the whole beam is reflected, so unlike an ordinary mirror nothing is lost to absorption. The critical angle for glass and air is about 42°. This principle makes diamonds sparkle, carries signals through optical fibres and explains mirages. Option A is wrong because light going from rarer to denser bends towards the normal and can never be totally reflected. Option C is wrong for the same reason, and it also wrongly speaks of loss. Option D is wrong because total internal reflection loses no intensity. Exam tip: two conditions, denser to rarer and angle greater than the critical angle; optical fibres use it.