True or False: In refraction, light travelling from a less dense medium to a more dense medium slows down.

In the context of refraction, it is indeed true that light traveling from a less dense medium to a more dense medium slows down. Refraction occurs when light passes from one medium into another medium with a different density, which can change its speed and direction.

When light moves from a medium like air (which is less dense) into a medium like water or glass (which are more dense), the change in density causes the speed of light to decrease. This slowing down of light leads to bending of its path towards the normal line (an imaginary line perpendicular to the surface at the point of entry). This principle is foundational in optics and is critical for understanding various optical devices like lenses.

Thus, the correct answer reflects a fundamental characteristic of how light interacts with different mediums in terms of speed and direction.