Refraction of visible light is the process by which light changes direction when it passes from one medium to another with a different optical density (like from air to water or glass). This occurs because light travels at different speeds in different materials.
Here’s how the process works:
- Change of Medium: When light passes from one transparent medium to another (e.g., air to glass), its speed changes.
- It slows down when entering a denser medium.
- It speeds up when moving into a less dense medium.
- Bending of Light: Due to the speed change, the light ray bends:
- Toward the normal (an imaginary line perpendicular to the surface) when entering a denser medium.
- Away from the normal when entering a less dense medium.
- Wavelength Change: The wavelength of light changes in the new medium, but its frequency remains constant.
- Emerging Ray: When the light exits the medium, it bends again. If it exits into the same medium it started in, the final ray is parallel to the original incident ray.
Example:
When a straw is placed in a glass of water, it appears bent or broken at the surface due to refraction. This effect is also responsible for phenomena like rainbows, lenses focusing light, and mirages.
Refraction is governed by Snell’s Law, which relates the angles of incidence and refraction to the refractive indices of the two media.