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Why does light bend when it passes from one material into another?

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A horizontal gradient bar displays the visible light spectrum from violet to red, labeled with corresponding frequency in terahertz, wavelength in nanometers, and photon energy in electron volts. — light When white light is spread apart by a prism or a diffraction grating, the colours of the visible spectrum appear. The colours vary according to their wavelengths. Violet has the highest frequencies and shortest wavelengths, and red has the lowest frequencies and the longest wavelengths.

Light bends when passing between different materials because its speed changes as it moves from one medium to another. This phenomenon is known as refraction.12

According to Huygens’s principle, light travels as a wave front. When this wave front hits the boundary between two media at an angle, one part of the wave enters the new material and changes speed before the rest of the wave does. Because different parts of the wave front are traveling at different speeds simultaneously, the wave front pivots, causing the light ray to change direction.31

The degree of this bending is determined by the refractive index of each material, which is a measure of how much the material slows down light compared to its speed in a vacuum. The relationship between the angles of the light ray and the refractive indices of the materials is described by Snell’s law. When light enters a medium with a higher refractive index, it slows down and bends toward the normal (the perpendicular line to the surface); conversely, it bends away from the normal when entering a medium with a lower refractive index.423