When a ray of light enters one medium from another medium, which quality will not change?

The answer is frequency.

When a ray of light enters one medium from another medium, the following will happen:

• The direction of the light ray will change. This is because the light ray will be refracted, or bent, as it passes from one medium to another. The amount of refraction depends on the refractive indices of the two media.
• The speed of the light ray will change. The speed of light is slower in a medium than in a vacuum. The amount of slowing down depends on the refractive index of the medium.
• The wavelength of the light ray will change. The wavelength of light is the distance between two consecutive crests or troughs of the light wave. The wavelength of light changes when the light ray passes from one medium to another. The amount of change in wavelength depends on the refractive indices of the two media.

The frequency of light is the number of waves that pass a given point in a given amount of time. The frequency of light does not change when the light ray passes from one medium to another. This is because the frequency of light is determined by the source of the light, and the source of the light does not change when the light ray passes from one medium to another.

In conclusion, the quality of light that does not change when a ray of light enters one medium from another medium is frequency.