When light passes from one material to another, its speed changes depending on the optical properties of the material, mainly its refractive index.
How Speed of Light Changes in Different Materials:
- In vacuum: Light travels at its maximum speed, about 299,792 kilometers per second.
- In other materials: Light slows down because the material’s atoms interact with the light waves, causing a delay in propagation.
Factors affecting speed:
- Refractive index (n): The speed of light in a material is the speed in vacuum divided by the refractive index of that material.
- For example:
- In air, n is very close to 1, so light speed is nearly the same as in vacuum.
- In water, n ≈ 1.33, so light travels about 1.33 times slower than in vacuum.
- In glass, n ≈ 1.5, so light travels roughly 1.5 times slower.
- For example:
Why does speed change?
- When light enters a material, it is absorbed and re-emitted by atoms, causing tiny delays.
- These delays accumulate, making the effective speed of the light wave slower through the material.
Summary:
- The speed of light decreases as it enters denser materials with higher refractive indices.
- This slowing down causes light to bend or refract at the interface between different materials.