What causes light to refract when passing through different mediums?

Light refracts when passing through different mediums due to the change in its speed, which alters its direction of propagation.

Refraction is a fundamental concept in physics, particularly in the study of optics. It refers to the bending of light as it passes from one medium to another. This bending is caused by a change in the speed of light. When light travels from a medium of one refractive index to another medium with a different refractive index, its speed changes, causing it to change direction. This is what we observe as refraction.

The refractive index of a medium is a measure of how much the speed of light is reduced inside the medium compared to its speed in a vacuum. The greater the refractive index, the slower light travels in that medium, and the more it bends. For example, light travels slower in water than in air, so it bends more when it enters water from air. This is why a straw in a glass of water appears bent at the water's surface.

The angle at which light hits the boundary between two mediums also affects how much it refracts. This is described by Snell's Law, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities of light in the two mediums, or equivalently, to the inverse ratio of the refractive indices.

In summary, refraction is caused by the change in speed of light when it passes from one medium to another, which alters its direction of propagation. The degree of refraction depends on the refractive indices of the two mediums and the angle at which the light hits the boundary.