Describe how wavefronts change during refraction.

Wavefronts change their speed, direction and spacing during refraction, conforming to Snell's law.

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another. The change in speed of the wavefronts as they pass from one medium to another causes them to change direction, a phenomenon known as bending of the wavefronts. This bending is what we refer to as refraction.

The degree of bending, or refraction, is determined by the indices of refraction of the two media. The index of refraction of a medium is a measure of how much the speed of light, or any wave, is reduced inside the medium compared to its speed in a vacuum. When a wavefront enters a medium with a higher index of refraction, it slows down and the wavefront bends towards the normal. Conversely, when it enters a medium with a lower index of refraction, it speeds up and the wavefront bends away from the normal.

The change in direction of the wavefronts is governed 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 equivalent to the ratio of the velocity of light in the original medium to the velocity of light in the refracting medium. This can also be expressed as the ratio of the indices of refraction.

The spacing of the wavefronts also changes during refraction. If the wavefronts slow down upon entering the new medium (i.e., the medium has a higher index of refraction), they get closer together. If they speed up (i.e., the medium has a lower index of refraction), they spread out. This change in spacing is directly related to the change in speed of the wavefronts, and it results in a change in the wavelength of the light.

In summary, during refraction, wavefronts undergo changes in speed, direction, and spacing. These changes are governed by the properties of the media the wavefronts are travelling through and are described by Snell's law.