The Fundamental Reason:
* Light is a wave: Light travels as an electromagnetic wave.
* Interaction with matter: When light enters a new medium (like from air to water), its wave interacts with the atoms and molecules of that material.
* Delay in propagation: This interaction causes a slight delay in the light's propagation.
How Speed Changes:
* Slower in denser media: The denser the medium, the more light interacts with it, and the slower it travels. This is why light slows down when it enters water or glass, which are denser than air.
* Faster in less dense media: In less dense media, like a vacuum, light travels at its maximum speed. This is the speed of light in a vacuum, which is a constant, denoted by 'c' (approximately 299,792,458 meters per second).
* Refraction: This change in speed is the reason why light bends when it enters a different medium. This bending is called refraction, and it's what allows us to see through lenses and prisms.
Key Points:
* Frequency stays the same: While the speed of light changes, its frequency (the number of waves passing a point per second) remains constant.
* Wavelength changes: To accommodate the change in speed, the wavelength (the distance between two crests of a wave) of light changes.
* Index of refraction: The ratio of the speed of light in a vacuum to the speed of light in a given medium is called the index of refraction. Higher index of refraction means slower speed.
In summary:
Light slows down as it enters a denser medium due to its interaction with the material. The frequency of light stays the same, but its wavelength changes to accommodate the change in speed. This change in speed causes light to bend, which is known as refraction.
