Refraction occurs when light changes direction as it passes from one medium to another because its speed changes.
Imagine a car moving from a paved road onto sand at an angle, as described in the reference (1:29-4:52 in the referenced video).
The Analogy Explained
- Car on the Road: When the car is entirely on the paved road, it travels in a straight line.
- Moving onto Sand: As one front wheel hits the sand before the other, that side of the car slows down because of the increased friction from the sand. The other side is still on the faster road. This difference in speed across the front of the car causes it to pivot or change direction.
- Car on the Sand: Once the whole car is on the sand, it continues in a straight line, but it is now traveling along a different path than it was on the road.
How Light Rays Refract
According to the reference, light rays work in the same way as this car analogy.
- Light in One Medium: Light travels in a straight line within a single, uniform medium (like air or water).
- Moving Between Media: When light rays move from one medium into another (e.g., from air into water, or from glass back into air), its speed changes.
- Change in Direction: If the light enters the new medium at an angle (not perpendicular), one part of the wavefront enters the new medium and slows down (or speeds up) before the other part. This difference in speed across the wavefront causes the light ray to bend or change direction. This bending is called refraction.
Key Factors Influencing Refraction
- Change in Speed: The fundamental cause is the change in the speed of light as it enters a different medium. Light travels at different speeds in different materials.
- Angle of Incidence: Refraction occurs when light hits the boundary between two media at an angle. If light hits perpendicularly, it slows down but continues in the same direction (no bending).
- Optical Density: The amount by which a medium slows down light is related to its optical density. Light bends towards the normal (an imaginary line perpendicular to the surface) when it enters a denser medium (where it slows down) and bends away from the normal when it enters a less dense medium (where it speeds up).
In essence, refraction is the bending of light due to its change in speed when transitioning between different substances.
