The Fundamental Principle: Snell's Law
The bending of light as it travels from one medium to another is governed by a fundamental principle called Snell's Law:
* n1 * sin(θ1) = n2 * sin(θ2)
Where:
* n1 and n2 are the refractive indices of the first and second media, respectively. The refractive index is a measure of how much light slows down in a medium compared to a vacuum.
* θ1 is the angle of incidence (the angle the light ray makes with the normal to the surface).
* θ2 is the angle of refraction (the angle the light ray makes with the normal after entering the second medium).
The Explanation
1. Speed of Light: Light travels at different speeds in different materials. It travels fastest in a vacuum (approximately 300,000 km/s). When light enters a denser medium (like water or glass), it slows down.
2. Wavefronts: Light can be visualized as a series of wavefronts. When a wavefront hits the boundary between two media, one part of the wavefront enters the new medium before the other part.
3. Changing Direction: Because the speed of light changes, the part of the wavefront that enters the new medium first slows down. This causes the wavefront to bend.
Bending Towards or Away from the Normal
* From a less dense to a denser medium: When light travels from a less dense medium (like air) to a denser medium (like water), it slows down. This causes the light to bend towards the normal.
* From a denser to a less dense medium: When light travels from a denser medium (like water) to a less dense medium (like air), it speeds up. This causes the light to bend away from the normal.
Visual Example:
Imagine a car driving on a smooth road that suddenly hits a patch of mud. The wheels on one side of the car enter the mud first and slow down, causing the car to turn slightly towards the mud. Similarly, the wavefront of light bends when entering a different medium.
Key Takeaway
The bending of light, known as refraction, is a consequence of the speed of light changing as it travels from one medium to another. This change in speed causes the wavefront to bend, either towards or away from the normal, depending on the relative densities of the media.
