What does refraction primarily cause light to do?

Refraction primarily causes light to change direction as it passes from one medium to another, such as air to water. This bending of light occurs due to the difference in the speed of light in different materials. When light enters a medium where its speed is different, it changes direction at the interface between the two mediums.

For example, when light moves from air (a less dense medium) into water (a denser medium), it slows down and bends toward the normal line (the imaginary line perpendicular to the surface). This principle can be observed in everyday situations, like when a straw appears bent when placed in a glass of water.

The other options involve concepts that are not directly related to the primary effect of refraction. Temperature changes occur due to heat energy rather than the bending of light, density relates to the mass of an object per unit volume and isn’t affected by light as it refracts, and color change involves the wavelength of light, which can be influenced by other phenomena like scattering or absorption, but is not the primary result of refraction itself. Therefore, the main and defining characteristic of refraction is the change in direction of light.